Update source files

.cargo/config.toml

@@ -0,0 +1,11 @@
+[target.wasm32-unknown-unknown]
+rustflags = ['--cfg', 'getrandom_backend="wasm_js"', '--cfg=web_sys_unstable_apis']
+
+# for Linux
+[target.x86_64-unknown-linux-gnu]
+linker = "clang"
+rustflags = ["-C", "link-arg=-fuse-ld=lld"]
+
+# for Windows
+# [target.x86_64-pc-windows-msvc]
+# linker = "rust-lld.exe"

.github/workflows/builds.yml

@@ -0,0 +1,177 @@
+name: Builds
+on:
+  - push
+env:
+  CARGO_TERM_COLOR: always
+  RUST_VERSION: "stable"
+jobs:
+  desktop:
+    name: Desktop (${{ matrix.target.os }} / ${{ matrix.target.arch }})
+    runs-on: ${{ matrix.target.runner }}
+    strategy:
+      fail-fast: false
+      matrix:
+        target:
+          - os: linux
+            arch: x86_64
+            runner: ubuntu-22.04
+            rust_target: x86_64-unknown-linux-gnu
+          - os: macos
+            arch: x86_64
+            runner: macos-15-intel
+            rust_target: x86_64-apple-darwin
+          - os: macos
+            arch: aarch64
+            runner: macos-latest
+            rust_target: aarch64-apple-darwin
+          - os: windows
+            arch: x86_64
+            runner: windows-latest
+            rust_target: x86_64-pc-windows-msvc
+          - os: windows
+            arch: aarch64
+            runner: windows-latest
+            rust_target: aarch64-pc-windows-msvc
+    steps:
+      - uses: actions/checkout@v5
+      - name: Setup Rust
+        uses: dtolnay/rust-toolchain@master
+        with:
+          toolchain: ${{ env.RUST_VERSION }}
+          components: rustfmt, clippy
+          targets: ${{ matrix.target.rust_target }}
+      - name: Rust cache
+        uses: Swatinem/rust-cache@v2
+      - name: Setup pnpm
+        uses: pnpm/action-setup@v4
+        with:
+          version: 10
+      - name: Setup Node
+        uses: actions/setup-node@v5
+        with:
+          node-version: 20
+          cache: pnpm
+          cache-dependency-path: frontend/pnpm-lock.yaml
+      - name: Install frontend dependencies
+        run: pnpm install --frozen-lockfile --prefer-offline
+        working-directory: frontend
+      - name: Cache Tauri CLI (macOS only)
+        if: matrix.target.os == 'macos'
+        id: cache-tauri-cli
+        uses: actions/cache@v4
+        with:
+          path: ~/.cargo/bin/cargo-tauri
+          key: ${{ runner.os }}-${{ runner.arch }}-tauri-cli-2
+      - name: Install cargo-binstall
+        if: matrix.target.os != 'macos'
+        uses: taiki-e/install-action@cargo-binstall
+      - name: Install Tauri CLI (via binstall)
+        if: matrix.target.os != 'macos'
+        run: cargo binstall tauri-cli --version '^2' --no-confirm
+      - name: Install Tauri CLI (from source on macOS)
+        if: matrix.target.os == 'macos' && steps.cache-tauri-cli.outputs.cache-hit != 'true'
+        run: cargo install tauri-cli --version '^2' --locked
+        env:
+          CARGO_PROFILE_RELEASE_LTO: false
+      - name: Cache apt packages
+        if: matrix.target.os == 'linux'
+        uses: actions/cache@v4
+        with:
+          path: |
+            /var/cache/apt/archives/*.deb
+          key: ${{ matrix.target.runner }}-apt-${{ hashFiles('**/Cargo.lock') }}
+          restore-keys: |
+            ${{ matrix.target.runner }}-apt-
+      - name: Install Linux dependencies
+        if: matrix.target.os == 'linux'
+        run: |
+          sudo apt-get update -qq && sudo apt-get install -y --no-install-recommends \
+            build-essential \
+            libglib2.0-dev \
+            libwebkit2gtk-4.1-dev \
+            libayatana-appindicator3-dev \
+            librsvg2-dev \
+            patchelf
+      - name: Build desktop app
+        run: cargo tauri build --target ${{ matrix.target.rust_target }}
+      - name: Upload artifacts
+        uses: actions/upload-artifact@v4
+        with:
+          name: iron-borders-${{ matrix.target.os }}-${{ matrix.target.arch }}
+          path: |
+            target/${{ matrix.target.rust_target }}/release/*.exe
+            target/${{ matrix.target.rust_target }}/release/bundle/appimage/*.AppImage
+            target/${{ matrix.target.rust_target }}/release/bundle/deb/*.deb
+            target/${{ matrix.target.rust_target }}/release/bundle/rpm/*.rpm
+            target/${{ matrix.target.rust_target }}/release/bundle/dmg/*.dmg
+          if-no-files-found: ignore
+  browser:
+    name: Browser (WASM)
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v5
+      - name: Install Rust
+        uses: dtolnay/rust-toolchain@master
+        with:
+          toolchain: ${{ env.RUST_VERSION }}
+          targets: x86_64-unknown-linux-gnu, wasm32-unknown-unknown
+      - uses: Swatinem/rust-cache@v2
+      - name: Setup pnpm
+        uses: pnpm/action-setup@v4
+        with:
+          version: 10
+      - name: Setup Node
+        uses: actions/setup-node@v5
+        with:
+          node-version: 20
+          cache: pnpm
+          cache-dependency-path: frontend/pnpm-lock.yaml
+      - name: Install frontend dependencies
+        run: pnpm install --frozen-lockfile --prefer-offline
+        working-directory: frontend
+      - name: Install wasm-bindgen-cli
+        uses: taiki-e/install-action@v2
+        with:
+          tool: wasm-bindgen-cli@0.2.104
+      - name: Install wasm-opt
+        uses: taiki-e/install-action@v2
+        with:
+          tool: wasm-opt@0.116.1
+      - name: Build WASM release
+        run: |
+          cargo build -p borders-wasm --profile wasm-release --target wasm32-unknown-unknown
+          wasm-bindgen --out-dir pkg --out-name borders --target web target/wasm32-unknown-unknown/wasm-release/borders_wasm.wasm
+          wasm-opt -Oz --enable-bulk-memory --enable-threads --all-features pkg/borders_bg.wasm -o pkg/borders_bg.wasm
+          mkdir -p frontend/pkg
+          cp -r pkg/* frontend/pkg/
+      - name: Build frontend (root-based)
+        run: pnpm run build:browser
+        working-directory: frontend
+      - name: Upload browser artifacts
+        uses: actions/upload-artifact@v4
+        with:
+          name: iron-borders-browser
+          path: frontend/dist/browser/client/**/*
+          if-no-files-found: error
+  deploy-cloudflare:
+    name: Deploy to Cloudflare Pages
+    needs: browser
+    runs-on: ubuntu-latest
+    if: github.event_name == 'push'
+    steps:
+      - name: Download browser artifact
+        uses: actions/download-artifact@v4
+        with:
+          name: iron-borders-browser
+          path: dist
+      - name: Deploy to Cloudflare Pages
+        id: deploy
+        uses: cloudflare/wrangler-action@v3
+        with:
+          apiToken: ${{ secrets.CLOUDFLARE_API_TOKEN }}
+          accountId: ${{ secrets.CLOUDFLARE_ACCOUNT_ID }}
+          command: pages deploy dist --project-name=borders
+      - name: Print deployment URL
+        env:
+          DEPLOYMENT_URL: ${{ steps.deploy.outputs.deployment-url }}
+        run: echo "Deployed to $DEPLOYMENT_URL"

.github/workflows/quality.yml

@@ -0,0 +1,84 @@
+name: Quality
+on:
+  - push
+env:
+  CARGO_TERM_COLOR: always
+  RUST_VERSION: "stable"
+jobs:
+  rust-quality:
+    name: Rust Quality
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v5
+      - name: Install Rust
+        uses: dtolnay/rust-toolchain@master
+        with:
+          toolchain: ${{ env.RUST_VERSION }}
+          targets: x86_64-unknown-linux-gnu, wasm32-unknown-unknown
+      - uses: Swatinem/rust-cache@v2
+      - name: Cache apt packages
+        uses: actions/cache@v4
+        with:
+          path: |
+            /var/cache/apt/archives/*.deb
+          key: ubuntu-latest-apt-${{ hashFiles('**/Cargo.lock') }}
+          restore-keys: |
+            ubuntu-latest-apt-
+      - name: Install Linux dependencies
+        run: |
+          sudo apt-get update -qq && sudo apt-get install -y --no-install-recommends \
+            build-essential \
+            libglib2.0-dev \
+            libwebkit2gtk-4.1-dev \
+            libayatana-appindicator3-dev \
+            librsvg2-dev \
+            patchelf
+      - name: Install just
+        uses: taiki-e/install-action@just
+      - name: Install cargo-machete
+        uses: taiki-e/install-action@cargo-machete
+      - name: Run Rust checks
+        run: just --shell bash --shell-arg -c check
+      - name: Install cargo-audit
+        uses: taiki-e/install-action@cargo-audit
+      - name: Run security audit
+        run: cargo audit
+  frontend-quality:
+    name: Frontend Quality
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v5
+      - name: Setup pnpm
+        uses: pnpm/action-setup@v4
+        with:
+          version: 10
+      - name: Setup Node
+        uses: actions/setup-node@v5
+        with:
+          node-version: 20
+          cache: pnpm
+          cache-dependency-path: frontend/pnpm-lock.yaml
+      - name: Install Rust
+        uses: dtolnay/rust-toolchain@master
+        with:
+          toolchain: ${{ env.RUST_VERSION }}
+          targets: x86_64-unknown-linux-gnu, wasm32-unknown-unknown
+      - uses: Swatinem/rust-cache@v2
+      - name: Install wasm-bindgen-cli
+        uses: taiki-e/install-action@v2
+        with:
+          tool: wasm-bindgen-cli@0.2.104
+      - name: Install frontend dependencies
+        run: pnpm install --frozen-lockfile
+        working-directory: frontend
+      - name: Install just
+        uses: taiki-e/install-action@just
+      - name: Build WASM for frontend checks
+        run: |
+          cargo build -p borders-wasm --profile wasm-dev --target wasm32-unknown-unknown
+          wasm-bindgen --out-dir pkg --out-name borders --target web target/wasm32-unknown-unknown/wasm-dev/borders_wasm.wasm
+          mkdir -p frontend/pkg
+          cp -r pkg/* frontend/pkg/
+      - name: Run frontend TypeScript checks
+        run: pnpm run build:browser
+        working-directory: frontend

.gitignore

@@ -0,0 +1,33 @@
+target/
+pkg/
+*.pem
+/*.io/
+releases/
+
+# Build-copied shader files
+frontend/public/assets/
+
+# Logs
+logs
+*.log
+npm-debug.log*
+yarn-debug.log*
+yarn-error.log*
+pnpm-debug.log*
+lerna-debug.log*
+
+node_modules
+dist
+dist-ssr
+*.local
+
+# Editor directories and files
+.vscode/*
+!.vscode/extensions.json
+.idea
+.DS_Store
+*.suo
+*.ntvs*
+*.njsproj
+*.sln
+*.sw?

.source-commit

@@ -0,0 +1 @@
+a4d0597beda33b4e9da45dc29d66bf6ccff15e37

Cargo.toml

@@ -0,0 +1,47 @@
+[workspace]
+members = [
+    "crates/borders-core",
+    "crates/borders-desktop",
+    "crates/borders-wasm",
+    "crates/borders-server",
+]
+resolver = "2"
+
+[workspace.package]
+authors = ["Xevion"]
+edition = "2024"
+version = "0.6.1"
+
+# Enable a small amount of optimization in the dev profile.
+[profile.dev]
+opt-level = 1
+
+# Enable a large amount of optimization in the dev profile for dependencies.
+[profile.dev.package."*"]
+opt-level = 3
+
+# Enable more optimization in the release profile at the cost of compile time.
+[profile.release]
+# Compile the entire crate as one unit.
+# Slows compile times, marginal improvements.
+codegen-units = 1
+# Do a second optimization pass over the entire program, including dependencies.
+# Slows compile times, marginal improvements.
+lto = "thin"
+
+# Development profile for WASM builds (faster compile times)
+[profile.wasm-dev]
+inherits = "dev"
+opt-level = 1
+panic = "abort"
+
+# Size optimization profile for WASM builds
+[profile.wasm-release]
+inherits = "release"
+incremental = false
+debug = false
+opt-level = "s"      # Optimize for size
+lto = true           # Link-time optimization
+codegen-units = 1    # Single codegen unit for better optimization
+panic = "abort"      # Smaller panic implementation
+strip = true         # Remove debug symbols

Justfile

@@ -0,0 +1,92 @@
+set shell := ["powershell"]
+
+default:
+    just --list
+
+check:
+    @echo "Running clippy (native)..."
+    @cargo clippy --all-targets --all-features --workspace -- -D warnings
+    @echo "Running cargo check (native)..."
+    @cargo check --all-targets --all-features --workspace
+    @echo "Running clippy (wasm32-unknown-unknown)..."
+    @cargo clippy --target wasm32-unknown-unknown --all-features -p borders-wasm -- -D warnings
+    @echo "Running cargo check (wasm32-unknown-unknown)..."
+    @cargo check --target wasm32-unknown-unknown --all-features -p borders-wasm
+    @echo "Running cargo machete..."
+    @cargo machete --with-metadata
+    @echo "All checks passed"
+
+check-ts:
+    @just _wasm-build wasm-dev
+    @echo "Running frontend checks..."
+    @pnpm run -C frontend check
+
+fix:
+    @echo "Running cargo fix..."
+    cargo fix --all-targets --all-features --workspace --allow-dirty
+
+wasm-dev: wasm-dev-build
+    pnpm -C frontend dev:browser --port 1421
+
+# Build WASM with the specified profile (wasm-dev or wasm-release)
+_wasm-build profile:
+    @$profile = "{{ profile }}"; \
+    $wasmFile = "target/wasm32-unknown-unknown/$profile/borders_wasm.wasm"; \
+    $pkgJs = "pkg/borders.js"; \
+    $pkgWasm = "pkg/borders_bg.wasm"; \
+    $frontendPkgJs = "frontend/pkg/borders.js"; \
+    $frontendPkgWasm = "frontend/pkg/borders_bg.wasm"; \
+    $beforeTime = if (Test-Path $wasmFile) { (Get-Item $wasmFile).LastWriteTime } else { $null }; \
+    cargo build -p borders-wasm --profile $profile --target wasm32-unknown-unknown; \
+    if ($LASTEXITCODE -ne 0) { exit $LASTEXITCODE }; \
+    $afterTime = if (Test-Path $wasmFile) { (Get-Item $wasmFile).LastWriteTime } else { $null }; \
+    $wasRebuilt = ($beforeTime -eq $null) -or ($afterTime -ne $beforeTime); \
+    $pkgExists = (Test-Path $pkgJs) -and (Test-Path $pkgWasm); \
+    $frontendPkgExists = (Test-Path $frontendPkgJs) -and (Test-Path $frontendPkgWasm); \
+    $isRelease = $profile -eq "wasm-release"; \
+    if ($wasRebuilt -or -not $pkgExists -or ($isRelease -and -not $frontendPkgExists)) { \
+        Write-Host "Running wasm-bindgen..."; \
+        wasm-bindgen --out-dir pkg --out-name borders --target web $wasmFile; \
+        if ($isRelease) { \
+            Write-Host "Running wasm-opt..."; \
+            wasm-opt -Oz --enable-bulk-memory --enable-threads --all-features pkg/borders_bg.wasm -o pkg/borders_bg.wasm; \
+        }; \
+    } else { \
+        Write-Host "WASM not rebuilt, skipping wasm-bindgen"; \
+    } \
+    New-Item -ItemType Directory -Force -Path 'frontend/pkg' | Out-Null; \
+    Copy-Item -Recurse -Force 'pkg/*' 'frontend/pkg/'; \
+    if ($isRelease) { \
+        Write-Host "Running frontend build..."; \
+        pnpm -C frontend build:browser; \
+    }; \
+
+# Development WASM build, unoptimized
+wasm-dev-build:
+    @just _wasm-build wasm-dev
+
+# Release WASM build, optimized
+wasm-release-build:
+    @just _wasm-build wasm-release
+
+wasm-release: wasm-release-build
+    @echo "Visit http://localhost:8080 to play"
+    caddy file-server --listen :8080 --root frontend/dist/browser/client --browse
+
+desktop-release:
+    cargo tauri build
+    target/release/borders-desktop.exe
+
+desktop-dev:
+    cargo tauri build --debug
+    target/debug/borders-desktop.exe
+
+# Run release manager CLI (handles setup specially)
+release *args:
+    @$firstArg = "{{ args }}".Split()[0]; \
+    if ($firstArg -eq "setup") { \
+        Write-Host "Installing release manager dependencies..."; \
+        pnpm install -C scripts/release-manager; \
+    } else { \
+        pnpm --silent -C scripts/release-manager exec tsx cli.ts {{ args }}; \
+    }

LICENSE

@@ -0,0 +1,13 @@
+Copyright © 2025 Ryan Walters. All Rights Reserved.
+
+This software and associated documentation files (the "Software") are proprietary
+and confidential. Unauthorized copying, modification, distribution, or use of this
+Software, via any medium, is strictly prohibited without the express written
+permission of the copyright holder.
+
+THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED,
+INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A
+PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT
+HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION
+OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE
+SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.

crates/borders-core/Cargo.toml

@@ -0,0 +1,89 @@
+[package]
+name = "borders-core"
+version.workspace = true
+edition.workspace = true
+authors.workspace = true
+
+[package.metadata.cargo-machete]
+ignored = ["serde_bytes", "chrono"]
+
+[features]
+default = ["ui"]
+ui = []
+
+[dependencies]
+anyhow = "1.0"
+async-trait = "0.1"
+bevy_ecs = { version = "0.17", default-features = false, features = ["std"] }
+bincode = { version = "2.0.1", features = ["serde"] }
+flume = "0.11"
+futures = "0.3"
+futures-lite = "2.6.1"
+glam = "0.30"
+hex = "0.4"
+hmac = "0.12"
+image = "0.25"
+once_cell = "1.20"
+rand = "0.9"
+serde = { version = "1.0", features = ["derive", "rc"] }
+slotmap = "1.0"
+serde_bytes = "0.11"
+serde_json = "1.0"
+sha2 = "0.10"
+tracing = "0.1"
+url = "2.5.0"
+web-transport = "0.9"
+
+# Target-specific dependencies to keep WASM builds compatible
+[target.'cfg(not(target_arch = "wasm32"))'.dependencies]
+tokio = { version = "1", features = [
+    "rt-multi-thread",
+    "macros",
+    "time",
+    "io-util",
+    "sync",
+] }
+reqwest = { version = "0.12", default-features = false, features = [
+    "json",
+    "rustls-tls",
+    "brotli",
+    "gzip",
+    "deflate",
+    "zstd",
+] }
+hickory-resolver = { version = "0.25", features = [
+    "tls-ring",
+    "https-ring",
+    "quic-ring",
+    "h3-ring",
+    "webpki-roots",
+] }
+uuid = { version = "1.11", features = ["v4", "serde"] }
+machineid-rs = "1.2"
+directories = "5.0"
+rustls-pemfile = "2.2.0"
+ring = "0.17.14"
+pem = "3.0.5"
+sysinfo = "0.33"
+
+[target.'cfg(windows)'.dependencies]
+winreg = "0.52"
+
+[target.'cfg(target_arch = "wasm32")'.dependencies]
+tokio = { version = "1", features = ["rt", "macros", "time", "io-util"] }
+reqwest = { version = "0.12", default-features = false, features = ["json"] }
+uuid = { version = "1.11", features = ["v4", "serde", "js"] }
+js-sys = "0.3"
+wasm-bindgen = "0.2"
+wasm-bindgen-futures = "0.4"
+gloo-timers = { version = "0.3", features = ["futures"] }
+web-sys = { version = "0.3", features = [
+    "BroadcastChannel",
+    "MessageEvent",
+    "Navigator",
+    "Window",
+] }
+web-time = "1.1"
+
+[build-dependencies]
+chrono = "0.4"

crates/borders-core/assets/maps/World.json

@@ -0,0 +1,76 @@
+{
+  "tiles": [
+    {
+      "color": "#000000",
+      "name": "Water",
+      "colorBase": "water",
+      "colorVariant": 4,
+      "conquerable": false,
+      "navigable": true
+    },
+    {
+      "color": "#222222",
+      "name": "Water",
+      "colorBase": "water",
+      "colorVariant": 6,
+      "conquerable": false,
+      "navigable": true
+    },
+    {
+      "color": "#555555",
+      "name": "Water",
+      "colorBase": "water",
+      "colorVariant": 12,
+      "conquerable": false,
+      "navigable": true
+    },
+    {
+      "color": "#777777",
+      "name": "Water",
+      "colorBase": "water",
+      "colorVariant": 14,
+      "conquerable": false,
+      "navigable": true
+    },
+    {
+      "color": "#999999",
+      "name": "Land",
+      "colorBase": "mountain",
+      "colorVariant": 5,
+      "conquerable": true,
+      "navigable": false,
+      "expansionCost": 80,
+      "expansionTime": 80
+    },
+    {
+      "color": "#BBBBBB",
+      "name": "Land",
+      "colorBase": "mountain",
+      "colorVariant": 9,
+      "conquerable": true,
+      "navigable": false,
+      "expansionCost": 70,
+      "expansionTime": 70
+    },
+    {
+      "color": "#DDDDDD",
+      "name": "Land",
+      "colorBase": "grass",
+      "colorVariant": 9,
+      "conquerable": true,
+      "navigable": false,
+      "expansionCost": 60,
+      "expansionTime": 60
+    },
+    {
+      "color": "#FFFFFF",
+      "name": "Land",
+      "colorBase": "grass",
+      "colorVariant": 6,
+      "conquerable": true,
+      "navigable": false,
+      "expansionCost": 50,
+      "expansionTime": 50
+    }
+  ]
+}

crates/borders-core/build.rs

@@ -0,0 +1,28 @@
+use std::env;
+use std::fs;
+use std::path::PathBuf;
+
+fn main() {
+    // Get the workspace root (two levels up from borders-core)
+    let manifest_dir = PathBuf::from(env::var("CARGO_MANIFEST_DIR").unwrap());
+    let workspace_root = manifest_dir.parent().unwrap().parent().unwrap();
+
+    // Read git commit from .source-commit file
+    let source_commit_path = workspace_root.join(".source-commit");
+    let git_commit = if source_commit_path.exists() {
+        fs::read_to_string(&source_commit_path).unwrap_or_else(|_| "unknown".to_string()).trim().to_string()
+    } else {
+        // Fallback to git command if file doesn't exist (local development)
+        std::process::Command::new("git").args(["rev-parse", "HEAD"]).current_dir(workspace_root).output().ok().and_then(|output| if output.status.success() { String::from_utf8(output.stdout).ok() } else { None }).map(|s| s.trim().to_string()).unwrap_or_else(|| "unknown".to_string())
+    };
+
+    // Get current build time in UTC
+    let build_time = chrono::Utc::now().to_rfc3339();
+
+    // Set environment variables for compile-time access
+    println!("cargo:rustc-env=BUILD_GIT_COMMIT={}", git_commit);
+    println!("cargo:rustc-env=BUILD_TIME={}", build_time);
+
+    // Re-run if .source-commit changes
+    println!("cargo:rerun-if-changed={}", source_commit_path.display());
+}

crates/borders-core/src/app.rs

@@ -0,0 +1,140 @@
+//! Minimal ECS app wrapper to replace Bevy's App
+
+use bevy_ecs::message::{Message, Messages};
+use bevy_ecs::prelude::*;
+use bevy_ecs::schedule::{IntoScheduleConfigs, ScheduleLabel, Schedules};
+use bevy_ecs::system::ScheduleSystem;
+use std::fmt::Debug;
+
+#[derive(Debug, Hash, PartialEq, Eq, Clone, ScheduleLabel)]
+pub struct Startup;
+
+#[derive(Debug, Hash, PartialEq, Eq, Clone, ScheduleLabel)]
+pub struct Update;
+
+#[derive(Debug, Hash, PartialEq, Eq, Clone, ScheduleLabel)]
+pub struct Last;
+
+#[derive(Debug, Hash, PartialEq, Eq, Clone, ScheduleLabel)]
+pub struct Fixed;
+
+pub struct App {
+    world: World,
+}
+
+impl App {
+    pub fn new() -> Self {
+        let mut world = World::new();
+
+        // Initialize schedules
+        let mut schedules = Schedules::new();
+        schedules.insert(Schedule::new(Startup));
+        schedules.insert(Schedule::new(Update));
+        schedules.insert(Schedule::new(Last));
+        schedules.insert(Schedule::new(Fixed));
+
+        world.insert_resource(schedules);
+
+        Self { world }
+    }
+
+    pub fn world(&self) -> &World {
+        &self.world
+    }
+
+    pub fn world_mut(&mut self) -> &mut World {
+        &mut self.world
+    }
+
+    pub fn insert_resource<R: Resource>(&mut self, resource: R) -> &mut Self {
+        self.world.insert_resource(resource);
+        self
+    }
+
+    pub fn init_resource<R: Resource + FromWorld>(&mut self) -> &mut Self {
+        self.world.init_resource::<R>();
+        self
+    }
+
+    pub fn insert_non_send_resource<R: 'static>(&mut self, resource: R) -> &mut Self {
+        self.world.insert_non_send_resource(resource);
+        self
+    }
+
+    pub fn add_message<M: Message>(&mut self) -> &mut Self {
+        if !self.world.contains_resource::<Messages<M>>() {
+            self.world.init_resource::<Messages<M>>();
+
+            // Add system to update this message type each frame
+            self.add_systems(Last, |mut messages: ResMut<Messages<M>>| {
+                messages.update();
+            });
+        }
+        self
+    }
+
+    pub fn add_systems<M>(&mut self, schedule: impl ScheduleLabel, systems: impl IntoScheduleConfigs<ScheduleSystem, M>) -> &mut Self {
+        let mut schedules = self.world.resource_mut::<Schedules>();
+        if let Some(schedule_inst) = schedules.get_mut(schedule) {
+            schedule_inst.add_systems(systems);
+        }
+        self
+    }
+
+    pub fn update(&mut self) {
+        // Remove schedules temporarily to avoid resource_scope conflicts
+        let mut schedules = self.world.remove_resource::<Schedules>().unwrap();
+
+        // Run Update schedule
+        if let Some(schedule) = schedules.get_mut(Update) {
+            schedule.run(&mut self.world);
+        }
+
+        // Run Last schedule (includes event updates)
+        if let Some(schedule) = schedules.get_mut(Last) {
+            schedule.run(&mut self.world);
+        }
+
+        // Re-insert schedules
+        self.world.insert_resource(schedules);
+    }
+
+    pub fn run_startup(&mut self) {
+        // Remove schedules temporarily to avoid resource_scope conflicts
+        let mut schedules = self.world.remove_resource::<Schedules>().unwrap();
+
+        // Run Startup schedule
+        if let Some(schedule) = schedules.get_mut(Startup) {
+            schedule.run(&mut self.world);
+        }
+
+        // Re-insert schedules
+        self.world.insert_resource(schedules);
+    }
+
+    pub fn finish(&mut self) {
+        // Finalize schedules
+        let mut schedules = self.world.remove_resource::<Schedules>().unwrap();
+
+        for (_, schedule) in schedules.iter_mut() {
+            schedule.graph_mut().initialize(&mut self.world);
+        }
+
+        self.world.insert_resource(schedules);
+    }
+
+    pub fn cleanup(&mut self) {
+        // Any cleanup needed before running
+    }
+}
+
+impl Default for App {
+    fn default() -> Self {
+        Self::new()
+    }
+}
+
+/// Plugin trait for modular setup
+pub trait Plugin {
+    fn build(&self, app: &mut App);
+}

crates/borders-core/src/build_info.rs

@@ -0,0 +1,21 @@
+//! Build metadata injected at compile time
+
+/// The version of the application from Cargo.toml
+pub const VERSION: &str = env!("CARGO_PKG_VERSION");
+
+/// The git commit hash from .source-commit file or git command
+pub const GIT_COMMIT: &str = env!("BUILD_GIT_COMMIT");
+
+/// The build timestamp in RFC3339 format (UTC)
+pub const BUILD_TIME: &str = env!("BUILD_TIME");
+
+/// Get the git commit hash (short form, first 7 characters)
+pub fn git_commit_short() -> &'static str {
+    let full = GIT_COMMIT;
+    if full.len() >= 7 { &full[..7] } else { full }
+}
+
+/// Full build information formatted as a string
+pub fn info() -> String {
+    format!("Iron Borders v{} ({})\nBuilt: {}", VERSION, git_commit_short(), BUILD_TIME)
+}

crates/borders-core/src/constants.rs

@@ -0,0 +1,8 @@
+/// Game tick interval in milliseconds (10 TPS = 100ms per turn)
+pub const TICK_INTERVAL: u64 = 100;
+
+/// Number of bot players
+pub const BOT_COUNT: usize = 100;
+
+/// Spawn timeout duration in seconds
+pub const SPAWN_TIMEOUT_SECS: f32 = 2.0;

crates/borders-core/src/game/action.rs

@@ -0,0 +1,40 @@
+//! Game action system
+//!
+//! This module defines the core action types that can be performed in the game.
+//! Actions represent discrete game events that can be initiated by both human players
+//! and AI bots. They are processed deterministically during turn execution.
+
+use serde::{Deserialize, Serialize};
+
+/// Core game action type
+///
+/// This enum represents all possible actions that can be performed in the game.
+/// Unlike `Intent`, which is a network-layer wrapper, `GameAction` is the actual
+/// game-level operation.
+///
+/// Actions can originate from:
+/// - Human players (via input systems → intents → network)
+/// - AI bots (calculated deterministically during turn execution)
+///
+/// All actions are processed in a deterministic order during `GameInstance::execute_turn()`.
+#[derive(Debug, Clone, Serialize, Deserialize, bincode::Encode, bincode::Decode)]
+pub enum GameAction {
+    /// Spawn a player's initial territory at a specific tile
+    ///
+    /// TODO: Remove this, it should be handled by a Turn0 special configuration AND the Intent::SetSpawn
+    Spawn { player_id: u16, tile_index: u32 },
+    /// Attack a target tile with a percentage of the player's total troops
+    Attack { player_id: u16, target_tile: u32, troops_ratio: f32 },
+    /// Launch a transport ship to attack across water
+    LaunchShip {
+        player_id: u16,
+        target_tile: u32,
+        /// Troops as a percentage (0-100) to avoid float precision issues
+        troops_percent: u32,
+    },
+    // Future action types:
+    // BuildStructure { player_id: u16, tile_index: u32, structure_type: StructureType },
+    // LaunchNuke { player_id: u16, target_tile: u32 },
+    // RequestAlliance { player_id: u16, target_player: u16 },
+    // DeclareWar { player_id: u16, target_player: u16 },
+}

crates/borders-core/src/game/borders.rs

@@ -0,0 +1,211 @@
+/// Border tile management
+///
+/// This module manages border tiles for all players. A border tile is a tile
+/// adjacent to a tile with a different owner. Borders are used for:
+/// - Attack targeting (attacks expand from border tiles)
+/// - UI rendering (show player borders on the map)
+/// - Ship launching (find coastal borders for naval operations)
+use std::collections::HashSet;
+
+use bevy_ecs::prelude::*;
+
+use crate::game::{
+    GameInstance,
+    player::{BorderTiles, PlayerId},
+    territory_manager::TerritoryManager,
+};
+
+/// Result of a border transition
+#[derive(Debug)]
+pub struct BorderTransitionResult {
+    /// Tiles that became interior (not borders anymore)
+    pub territory: Vec<usize>,
+    /// Tiles that are now attacker borders
+    pub attacker: Vec<usize>,
+    /// Tiles that are now defender borders
+    pub defender: Vec<usize>,
+}
+
+/// Manages border tiles for all players
+///
+/// A border tile is a tile adjacent to a tile with a different owner.
+/// This resource maintains efficient lookup of border tiles for attack
+/// targeting and UI rendering.
+///
+/// # Border Detection Algorithm
+///
+/// A tile is a border if any of its 4-directional neighbors has a different owner:
+/// - Water tiles have no owner and are never borders
+/// - Unclaimed tiles have no owner and are never borders
+/// - A tile surrounded entirely by same-owner tiles is interior (not a border)
+///
+/// # Future ECS Migration
+///
+/// This will eventually become a `BorderTiles` component on player entities,
+/// with a system to update borders after territory changes.
+#[derive(Resource)]
+pub struct BorderManager {
+    border_tiles: Vec<HashSet<usize>>,
+}
+
+impl Default for BorderManager {
+    fn default() -> Self {
+        Self::new()
+    }
+}
+
+impl BorderManager {
+    pub fn new() -> Self {
+        Self { border_tiles: Vec::new() }
+    }
+
+    /// Resets the border manager
+    ///
+    /// Should only be called when a new game is started
+    pub fn reset(&mut self, _width: u32, _height: u32, player_count: usize) {
+        self.border_tiles = vec![HashSet::new(); player_count];
+    }
+
+    /// Update borders after territory changes (e.g., conquest)
+    ///
+    /// A tile is a border if any neighbor has a different owner.
+    /// This method checks all affected tiles (conquered tiles + their neighbors)
+    /// and updates border sets accordingly.
+    pub fn update_after_conquest(&mut self, tiles: &HashSet<usize>, attacker: usize, defender: Option<usize>, territory_manager: &TerritoryManager) -> BorderTransitionResult {
+        let _ = tracing::debug_span!("border_transition");
+        let _span = tracing::trace_span!("border_transition", tile_count = tiles.len()).entered();
+
+        let mut result = BorderTransitionResult { territory: Vec::new(), attacker: Vec::new(), defender: Vec::new() };
+
+        // Collect all tiles to check: conquered tiles + all their neighbors
+        let mut tiles_to_check = HashSet::new();
+
+        for &tile in tiles {
+            tiles_to_check.insert(tile);
+
+            // Add all neighbors
+            territory_manager.on_neighbor_indices(tile, |neighbor| {
+                tiles_to_check.insert(neighbor);
+            });
+        }
+
+        // Remove conquered tiles from defender borders
+        if let Some(defender_id) = defender {
+            for &tile in tiles {
+                self.border_tiles[defender_id].remove(&tile);
+            }
+        }
+
+        // Update borders for all affected tiles
+        for &tile in &tiles_to_check {
+            // Skip if tile has no owner (water or unclaimed)
+            if !territory_manager.has_owner(tile) {
+                continue;
+            }
+
+            let owner_id = territory_manager.get_owner(tile);
+            let owner = owner_id as usize;
+
+            // Determine if this tile is a border
+            let is_border = Self::is_border_tile(tile, owner_id, territory_manager);
+
+            if is_border {
+                // Add to border set if not already present
+                if self.border_tiles[owner].insert(tile) {
+                    // Track for result
+                    if owner == attacker {
+                        result.attacker.push(tile);
+                    } else if Some(owner) == defender {
+                        result.defender.push(tile);
+                    }
+                }
+            } else {
+                // Remove from border set if present
+                if self.border_tiles[owner].remove(&tile) {
+                    // Tile became interior
+                    if owner == attacker {
+                        result.territory.push(tile);
+                    }
+                }
+            }
+        }
+
+        if tiles.len() > 50 {
+            tracing::trace!(tile_count = tiles.len(), "Large border transition");
+        }
+
+        result
+    }
+
+    /// Check if a tile is a border tile using simple neighbor logic
+    ///
+    /// A tile is a border if it has any neighbor with a different owner
+    fn is_border_tile(tile: usize, owner: u16, territory_manager: &TerritoryManager) -> bool {
+        let mut is_border = false;
+
+        territory_manager.on_neighbor_indices(tile, |neighbor| {
+            if territory_manager.get_owner(neighbor) != owner {
+                is_border = true;
+            }
+        });
+
+        is_border
+    }
+
+    /// Gets the border tiles of a player
+    pub fn get_border_tiles(&self, player: usize) -> &HashSet<usize> {
+        &self.border_tiles[player]
+    }
+}
+
+/// Update all player borders based on territory changes (batched system)
+///
+/// This system runs once per turn AFTER all territory changes (conquests, spawns, ships).
+/// It drains the TerritoryManager's change buffer and updates borders for all affected players.
+pub fn update_player_borders_system(mut players: Query<(&PlayerId, &mut BorderTiles)>, mut game_instance: ResMut<GameInstance>) {
+    if !game_instance.territory_manager.has_changes() {
+        return; // Early exit - no work needed
+    }
+
+    // Collect all changed tiles at once
+    let changed_tiles: HashSet<usize> = game_instance.territory_manager.iter_changes().collect();
+
+    // Build affected tiles (changed + all neighbors)
+    let mut affected_tiles = HashSet::with_capacity(changed_tiles.len() * 5);
+    for &tile in &changed_tiles {
+        affected_tiles.insert(tile);
+        game_instance.territory_manager.on_neighbor_indices(tile, |n| {
+            affected_tiles.insert(n);
+        });
+    }
+
+    // Update each player's borders (dual-write to resource and components)
+    for (player_id, mut component_borders) in &mut players {
+        update_borders_for_player(player_id.0, &mut component_borders.0, &affected_tiles, &game_instance.territory_manager);
+
+        // Dual-write: sync to resource for backward compatibility
+        game_instance.border_manager.border_tiles[player_id.0 as usize] = component_borders.0.clone();
+    }
+}
+
+/// Update borders for a single player based on affected tiles
+fn update_borders_for_player(player_id: u16, borders: &mut HashSet<usize>, affected_tiles: &HashSet<usize>, territory: &TerritoryManager) {
+    for &tile in affected_tiles {
+        let owner = territory.get_owner(tile);
+
+        // Skip tiles we don't own
+        if owner != player_id {
+            borders.remove(&tile);
+            continue;
+        }
+
+        // Check if it's a border (early exit when different owner found)
+        let is_border = territory.any_neighbor_has_different_owner(tile, player_id);
+
+        if is_border {
+            borders.insert(tile);
+        } else {
+            borders.remove(&tile);
+        }
+    }
+}

crates/borders-core/src/game/bot.rs

@@ -0,0 +1,521 @@
+use rand::rngs::StdRng;
+use rand::{Rng, SeedableRng};
+
+use crate::game::action::GameAction;
+use crate::game::borders::BorderManager;
+use crate::game::player::Player;
+use crate::game::territory_manager::TerritoryManager;
+
+/// Simple bot AI
+pub struct BotPlayer {
+    last_action_tick: u64,
+    action_cooldown: u64,
+}
+
+impl Default for BotPlayer {
+    fn default() -> Self {
+        Self::new()
+    }
+}
+
+impl BotPlayer {
+    pub fn new() -> Self {
+        let mut rng = rand::rng();
+        Self {
+            last_action_tick: 0,
+            action_cooldown: rng.random_range(0..10), // 0-1 seconds
+        }
+    }
+
+    /// Tick the bot AI - now deterministic based on turn number and RNG seed
+    pub fn tick(&mut self, turn_number: u64, player: &Player, territory_manager: &TerritoryManager, border_manager: &BorderManager, rng_seed: u64) -> Option<GameAction> {
+        // Only act every few ticks
+        if turn_number < self.last_action_tick + self.action_cooldown {
+            return None;
+        }
+
+        self.last_action_tick = turn_number;
+
+        // Deterministic RNG based on turn number, player ID, and global seed
+        let seed = rng_seed.wrapping_add(turn_number).wrapping_add(player.id as u64);
+        let mut rng = StdRng::seed_from_u64(seed);
+        self.action_cooldown = rng.random_range(3..15);
+
+        // Decide action: expand into wilderness or attack a neighbor
+        let action_type: f32 = rng.random();
+
+        let action = if action_type < 0.6 {
+            // Expand into wilderness (60% chance)
+            self.expand_wilderness(player, territory_manager, border_manager, &mut rng)
+        } else {
+            // Attack a neighbor (40% chance)
+            self.attack_neighbor(player, territory_manager, border_manager, &mut rng)
+        };
+
+        let _span = tracing::debug_span!("bot_tick", player_id = player.id, has_action = action.is_some()).entered();
+        action
+    }
+
+    /// Expand into unclaimed territory
+    fn expand_wilderness(&self, player: &Player, territory_manager: &TerritoryManager, border_manager: &BorderManager, rng: &mut StdRng) -> Option<GameAction> {
+        let border_tiles = border_manager.get_border_tiles(player.id);
+
+        // Find a valid, unclaimed neighbor tile to attack
+        for &tile in border_tiles {
+            let x = tile as u32 % territory_manager.width();
+            let y = tile as u32 / territory_manager.width();
+
+            let neighbors = [(x > 0).then_some(tile - 1), (x < territory_manager.width() - 1).then_some(tile + 1), (y > 0).then_some(tile - territory_manager.width() as usize), (y < territory_manager.height() - 1).then_some(tile + territory_manager.width() as usize)];
+
+            for neighbor in neighbors.iter().flatten() {
+                if !territory_manager.has_owner(*neighbor) && !territory_manager.is_water(*neighbor) {
+                    // Found unclaimed land
+                    let troop_percentage: f32 = rng.random_range(0.1..0.3);
+                    return Some(GameAction::Attack { player_id: player.id as u16, target_tile: *neighbor as u32, troops_ratio: troop_percentage });
+                }
+            }
+        }
+
+        tracing::trace!(player_id = player.id, "No wilderness target found");
+        None
+    }
+
+    /// Attack a neighboring player
+    fn attack_neighbor(&self, player: &Player, territory_manager: &TerritoryManager, border_manager: &BorderManager, rng: &mut StdRng) -> Option<GameAction> {
+        // Find neighboring players
+        let mut neighbors = std::collections::HashSet::new();
+        let border_tiles = border_manager.get_border_tiles(player.id);
+
+        for &tile in border_tiles {
+            let x = tile as u32 % territory_manager.width();
+            let y = tile as u32 / territory_manager.width();
+
+            // Check all neighbors
+            if x > 0 {
+                let neighbor = tile - 1;
+                let ownership = territory_manager.get_ownership(neighbor);
+                if let Some(nation_id) = ownership.nation_id()
+                    && nation_id != player.id as u16
+                {
+                    neighbors.insert(nation_id as usize);
+                }
+            }
+            if x < territory_manager.width() - 1 {
+                let neighbor = tile + 1;
+                let ownership = territory_manager.get_ownership(neighbor);
+                if let Some(nation_id) = ownership.nation_id()
+                    && nation_id != player.id as u16
+                {
+                    neighbors.insert(nation_id as usize);
+                }
+            }
+            if y > 0 {
+                let neighbor = tile - territory_manager.width() as usize;
+                let ownership = territory_manager.get_ownership(neighbor);
+                if let Some(nation_id) = ownership.nation_id()
+                    && nation_id != player.id as u16
+                {
+                    neighbors.insert(nation_id as usize);
+                }
+            }
+            if y < territory_manager.height() - 1 {
+                let neighbor = tile + territory_manager.width() as usize;
+                let ownership = territory_manager.get_ownership(neighbor);
+                if let Some(nation_id) = ownership.nation_id()
+                    && nation_id != player.id as u16
+                {
+                    neighbors.insert(nation_id as usize);
+                }
+            }
+        }
+
+        if neighbors.is_empty() {
+            return None;
+        }
+
+        // Pick a random neighbor to attack
+        let neighbor_vec: Vec<_> = neighbors.into_iter().collect();
+        let target_id = neighbor_vec[rng.random_range(0..neighbor_vec.len())];
+
+        // To attack a player, we need to pick a specific tile.
+        // Let's find a border tile of the target player that is adjacent to us.
+        let target_border = border_manager.get_border_tiles(target_id);
+        for &target_tile in target_border {
+            let x = target_tile as u32 % territory_manager.width();
+            let y = target_tile as u32 / territory_manager.width();
+            let neighbor_indices = [(x > 0).then_some(target_tile - 1), (x < territory_manager.width() - 1).then_some(target_tile + 1), (y > 0).then_some(target_tile - territory_manager.width() as usize), (y < territory_manager.height() - 1).then_some(target_tile + territory_manager.width() as usize)];
+
+            for &neighbor_idx in neighbor_indices.iter().flatten() {
+                if territory_manager.get_owner(neighbor_idx) == player.id as u16 {
+                    // This is a valid attack target
+                    let troop_percentage: f32 = rng.random_range(0.2..0.5);
+                    return Some(GameAction::Attack { player_id: player.id as u16, target_tile: target_tile as u32, troops_ratio: troop_percentage });
+                }
+            }
+        }
+
+        None
+    }
+}
+
+/// Minimum distance (in tiles) between any two spawn points
+/// This ensures players and bots don't spawn too close together
+const MIN_SPAWN_DISTANCE: f32 = 70.0;
+
+/// Absolute minimum spawn distance to prevent exact overlaps
+/// Used as final fallback when map is very crowded
+const ABSOLUTE_MIN_DISTANCE: f32 = 5.0;
+
+/// Distance reduction factor per adaptive wave (15% reduction)
+const DISTANCE_REDUCTION_FACTOR: f32 = 0.85;
+
+/// Spatial grid for fast spawn collision detection
+/// Divides map into cells for O(1) neighbor queries instead of O(n)
+struct SpawnGrid {
+    grid: std::collections::HashMap<(i32, i32), Vec<usize>>,
+    cell_size: f32,
+    map_width: u32,
+}
+
+impl SpawnGrid {
+    fn new(cell_size: f32, map_width: u32) -> Self {
+        Self { grid: std::collections::HashMap::new(), cell_size, map_width }
+    }
+
+    fn insert(&mut self, tile: usize) {
+        let cell = self.tile_to_cell(tile);
+        self.grid.entry(cell).or_default().push(tile);
+    }
+
+    fn tile_to_cell(&self, tile: usize) -> (i32, i32) {
+        let x = (tile as u32 % self.map_width) as f32;
+        let y = (tile as u32 / self.map_width) as f32;
+        ((x / self.cell_size) as i32, (y / self.cell_size) as i32)
+    }
+
+    fn has_nearby(&self, tile: usize, radius: f32, map_width: u32) -> bool {
+        let cell = self.tile_to_cell(tile);
+        let cell_radius = (radius / self.cell_size).ceil() as i32;
+
+        for dx in -cell_radius..=cell_radius {
+            for dy in -cell_radius..=cell_radius {
+                let check_cell = (cell.0 + dx, cell.1 + dy);
+                if let Some(tiles) = self.grid.get(&check_cell) {
+                    for &existing_tile in tiles {
+                        if calculate_tile_distance(tile, existing_tile, map_width) < radius {
+                            return true;
+                        }
+                    }
+                }
+            }
+        }
+        false
+    }
+}
+
+/// Calculate Euclidean distance between two tiles
+fn calculate_tile_distance(tile1: usize, tile2: usize, map_width: u32) -> f32 {
+    let x1 = (tile1 as u32 % map_width) as f32;
+    let y1 = (tile1 as u32 / map_width) as f32;
+    let x2 = (tile2 as u32 % map_width) as f32;
+    let y2 = (tile2 as u32 / map_width) as f32;
+
+    let dx = x1 - x2;
+    let dy = y1 - y2;
+    (dx * dx + dy * dy).sqrt()
+}
+
+/// Manager for bot AI state and decision-making
+///
+/// BotManager is part of GameInstance and handles all bot decision-making
+/// in a deterministic way. Unlike the old Bevy-based bot system, this is
+/// part of the core game state and executes during turn processing.
+pub struct BotManager {
+    bots: Vec<BotPlayer>,
+    bot_player_ids: Vec<usize>,
+}
+
+impl BotManager {
+    /// Create a new BotManager with the specified number of bots
+    pub fn new(bot_count: usize, human_player_count: usize) -> Self {
+        let bots = (0..bot_count).map(|_| BotPlayer::new()).collect();
+
+        // Bot player IDs start after human players
+        // Human player is ID 0, so first bot is ID 1
+        let first_bot_id = human_player_count;
+        let bot_player_ids = (first_bot_id..(first_bot_id + bot_count)).collect();
+
+        Self { bots, bot_player_ids }
+    }
+
+    /// Get the number of bots
+    pub fn bot_count(&self) -> usize {
+        self.bots.len()
+    }
+
+    /// Get bot player IDs
+    pub fn bot_player_ids(&self) -> &[usize] {
+        &self.bot_player_ids
+    }
+
+    /// Calculate initial bot spawn positions (first pass)
+    ///
+    /// Places bots at random valid locations with adaptive spacing.
+    /// Uses spatial grid for O(1) neighbor checks and adaptively reduces
+    /// minimum distance when map becomes crowded.
+    ///
+    /// Guarantees all bots spawn (no silent drops). This is deterministic based on rng_seed.
+    ///
+    /// Returns Vec<(player_id, tile_index)> for each bot
+    pub fn calculate_initial_spawns(&self, territory_manager: &TerritoryManager, rng_seed: u64) -> Vec<(usize, usize)> {
+        let width = territory_manager.width();
+        let height = territory_manager.height();
+        let map_size = (width * height) as usize;
+
+        let mut spawn_positions = Vec::with_capacity(self.bot_player_ids.len());
+        let mut grid = SpawnGrid::new(MIN_SPAWN_DISTANCE, width);
+        let mut current_min_distance = MIN_SPAWN_DISTANCE;
+
+        for (bot_index, &player_id) in self.bot_player_ids.iter().enumerate() {
+            // Deterministic RNG for spawn location
+            let seed = rng_seed.wrapping_add(player_id as u64).wrapping_add(bot_index as u64);
+            let mut rng = StdRng::seed_from_u64(seed);
+
+            let mut placed = false;
+
+            // Try with current minimum distance
+            while !placed && current_min_distance >= ABSOLUTE_MIN_DISTANCE {
+                // Phase 1: Random sampling (1000 attempts)
+                for _ in 0..1000 {
+                    let tile = rng.random_range(0..map_size);
+
+                    // Check if tile is valid land
+                    if territory_manager.has_owner(tile) || territory_manager.is_water(tile) {
+                        continue;
+                    }
+
+                    // Check distance using spatial grid (O(1) instead of O(n))
+                    if !grid.has_nearby(tile, current_min_distance, width) {
+                        spawn_positions.push((player_id, tile));
+                        grid.insert(tile);
+                        placed = true;
+                        break;
+                    }
+                }
+
+                // Phase 2: Grid-guided fallback (if random sampling failed)
+                if !placed {
+                    // Try a systematic grid search with stride
+                    let stride = (current_min_distance * 0.8) as usize;
+                    let mut attempts = 0;
+                    for y in (0..height as usize).step_by(stride.max(1)) {
+                        for x in (0..width as usize).step_by(stride.max(1)) {
+                            let tile = y * width as usize + x;
+                            if tile >= map_size {
+                                continue;
+                            }
+
+                            if territory_manager.has_owner(tile) || territory_manager.is_water(tile) {
+                                continue;
+                            }
+
+                            if !grid.has_nearby(tile, current_min_distance, width) {
+                                spawn_positions.push((player_id, tile));
+                                grid.insert(tile);
+                                placed = true;
+                                break;
+                            }
+
+                            attempts += 1;
+                            if attempts > 200 {
+                                break;
+                            }
+                        }
+                        if placed {
+                            break;
+                        }
+                    }
+                }
+
+                // Phase 3: Reduce minimum distance and retry
+                if !placed {
+                    current_min_distance *= DISTANCE_REDUCTION_FACTOR;
+                    if bot_index % 100 == 0 && current_min_distance < MIN_SPAWN_DISTANCE {
+                        tracing::debug!("Adaptive spawn: reduced min_distance to {:.1} for bot {}", current_min_distance, bot_index);
+                    }
+                }
+            }
+
+            // Final fallback: Place at any valid land tile (guaranteed)
+            if !placed {
+                for _ in 0..10000 {
+                    let tile = rng.random_range(0..map_size);
+                    if !territory_manager.has_owner(tile) && !territory_manager.is_water(tile) {
+                        spawn_positions.push((player_id, tile));
+                        grid.insert(tile);
+                        placed = true;
+                        tracing::warn!("Bot {} placed with fallback (no distance constraint)", player_id);
+                        break;
+                    }
+                }
+            }
+
+            if !placed {
+                tracing::error!("Failed to place bot {} after all attempts", player_id);
+            }
+        }
+
+        spawn_positions
+    }
+
+    /// Recalculate bot spawns considering player positions (second pass)
+    ///
+    /// For any bot that is too close to a player spawn, find a new position.
+    /// Uses adaptive algorithm with grid acceleration to guarantee all displaced
+    /// bots find new positions. This maintains determinism while ensuring proper spawn spacing.
+    ///
+    /// Arguments:
+    /// - `initial_bot_spawns`: Bot positions from first pass
+    /// - `player_spawns`: Human player spawn positions
+    /// - `territory_manager`: For checking valid tiles
+    /// - `rng_seed`: For deterministic relocation
+    ///
+    /// Returns updated Vec<(player_id, tile_index)> with relocated bots
+    pub fn recalculate_spawns_with_players(&self, initial_bot_spawns: Vec<(usize, usize)>, player_spawns: &[(usize, usize)], territory_manager: &TerritoryManager, rng_seed: u64) -> Vec<(usize, usize)> {
+        let width = territory_manager.width();
+        let height = territory_manager.height();
+        let map_size = (width * height) as usize;
+
+        // Build spatial grid from player spawns and bots we're keeping
+        let mut grid = SpawnGrid::new(MIN_SPAWN_DISTANCE, width);
+        for &(_, tile) in player_spawns {
+            grid.insert(tile);
+        }
+
+        // Identify bots that need relocation
+        let mut bots_to_relocate = Vec::new();
+        let mut final_spawns = Vec::new();
+
+        for (player_id, tile) in initial_bot_spawns {
+            let mut needs_relocation = false;
+
+            // Check distance from all player spawns using grid
+            for &(_, player_tile) in player_spawns {
+                if calculate_tile_distance(tile, player_tile, width) < MIN_SPAWN_DISTANCE {
+                    needs_relocation = true;
+                    break;
+                }
+            }
+
+            if needs_relocation {
+                bots_to_relocate.push(player_id);
+            } else {
+                final_spawns.push((player_id, tile));
+                grid.insert(tile);
+            }
+        }
+
+        // Relocate bots using adaptive algorithm (same as calculate_initial_spawns)
+        let mut current_min_distance = MIN_SPAWN_DISTANCE;
+
+        for (reloc_index, &player_id) in bots_to_relocate.iter().enumerate() {
+            let seed = rng_seed.wrapping_add(player_id as u64).wrapping_add(0xDEADBEEF);
+            let mut rng = StdRng::seed_from_u64(seed);
+
+            let mut placed = false;
+
+            // Try with current minimum distance
+            while !placed && current_min_distance >= ABSOLUTE_MIN_DISTANCE {
+                // Phase 1: Random sampling (1000 attempts)
+                for _ in 0..1000 {
+                    let tile = rng.random_range(0..map_size);
+
+                    // Check if tile is valid land
+                    if territory_manager.has_owner(tile) || territory_manager.is_water(tile) {
+                        continue;
+                    }
+
+                    // Check distance using spatial grid (includes players + placed bots)
+                    if !grid.has_nearby(tile, current_min_distance, width) {
+                        final_spawns.push((player_id, tile));
+                        grid.insert(tile);
+                        placed = true;
+                        break;
+                    }
+                }
+
+                // Phase 2: Grid-guided fallback
+                if !placed {
+                    let stride = (current_min_distance * 0.8) as usize;
+                    let mut attempts = 0;
+                    for y in (0..height as usize).step_by(stride.max(1)) {
+                        for x in (0..width as usize).step_by(stride.max(1)) {
+                            let tile = y * width as usize + x;
+                            if tile >= map_size {
+                                continue;
+                            }
+
+                            if territory_manager.has_owner(tile) || territory_manager.is_water(tile) {
+                                continue;
+                            }
+
+                            if !grid.has_nearby(tile, current_min_distance, width) {
+                                final_spawns.push((player_id, tile));
+                                grid.insert(tile);
+                                placed = true;
+                                break;
+                            }
+
+                            attempts += 1;
+                            if attempts > 200 {
+                                break;
+                            }
+                        }
+                        if placed {
+                            break;
+                        }
+                    }
+                }
+
+                // Phase 3: Reduce minimum distance and retry
+                if !placed {
+                    current_min_distance *= DISTANCE_REDUCTION_FACTOR;
+                    if reloc_index % 50 == 0 && current_min_distance < MIN_SPAWN_DISTANCE {
+                        tracing::debug!("Adaptive relocation: reduced min_distance to {:.1} for bot {}", current_min_distance, reloc_index);
+                    }
+                }
+            }
+
+            // Final fallback: Place at any valid land tile (guaranteed)
+            if !placed {
+                for _ in 0..10000 {
+                    let tile = rng.random_range(0..map_size);
+                    if !territory_manager.has_owner(tile) && !territory_manager.is_water(tile) {
+                        final_spawns.push((player_id, tile));
+                        grid.insert(tile);
+                        placed = true;
+                        tracing::warn!("Bot {} relocated with fallback (no distance constraint)", player_id);
+                        break;
+                    }
+                }
+            }
+
+            if !placed {
+                tracing::error!("Failed to relocate bot {} after all attempts", player_id);
+            }
+        }
+
+        final_spawns
+    }
+
+    /// Calculate action for a specific bot
+    ///
+    /// This is deterministic - same inputs = same output
+    pub fn calculate_action(&mut self, bot_index: usize, turn_number: u64, player: &Player, territory_manager: &TerritoryManager, border_manager: &BorderManager, rng_seed: u64) -> Option<GameAction> {
+        if bot_index >= self.bots.len() {
+            return None;
+        }
+
+        self.bots[bot_index].tick(turn_number, player, territory_manager, border_manager, rng_seed)
+    }
+}

crates/borders-core/src/game/combat/active.rs

@@ -0,0 +1,256 @@
+/// Active attacks management
+///
+/// This module manages all ongoing attacks in the game. It provides efficient
+/// lookup and coordination of attacks, ensuring proper merging of attacks on
+/// the same target and handling counter-attacks.
+use std::collections::HashSet;
+
+use bevy_ecs::prelude::*;
+use slotmap::{SlotMap, new_key_type};
+
+new_key_type! {
+    /// Unique key for identifying attacks in the SlotMap
+    pub struct AttackKey;
+}
+
+use super::executor::{AttackConfig, AttackExecutor};
+use crate::game::rng::DeterministicRng;
+use crate::game::{borders::BorderManager, player::Player, territory_manager::TerritoryManager};
+
+/// Manages all active attacks in the game
+///
+/// This resource tracks ongoing attacks and provides efficient lookup
+/// by attacker/target relationships. Attacks progress over multiple turns
+/// until they run out of troops or conquerable tiles.
+///
+/// # Index Structures
+///
+/// Multiple index structures are maintained for fast lookup:
+/// - `player_index`: [attacker][target] → set of attack keys
+/// - `unclaimed_index`: [attacker] → attack key for unclaimed territory
+/// - `player_attack_list`: [player] → attacks where player is attacker
+/// - `target_attack_list`: [player] → attacks where player is target
+///
+/// Uses SlotMap for stable keys - no index shifting needed on removal.
+/// Uses HashSet for O(1) lookups and removals.
+#[derive(Resource)]
+pub struct ActiveAttacks {
+    attacks: SlotMap<AttackKey, AttackExecutor>,
+    player_index: Vec<Vec<HashSet<AttackKey>>>,  // [attacker][target] -> set of attack keys
+    unclaimed_index: Vec<Option<AttackKey>>,     // [attacker] -> attack key for unclaimed
+    player_attack_list: Vec<HashSet<AttackKey>>, // [player] -> set of attack keys where player is attacker
+    target_attack_list: Vec<HashSet<AttackKey>>, // [player] -> set of attack keys where player is target
+    width: u32,
+}
+
+impl Default for ActiveAttacks {
+    fn default() -> Self {
+        Self::new()
+    }
+}
+
+impl ActiveAttacks {
+    pub fn new() -> Self {
+        Self { attacks: SlotMap::with_key(), player_index: Vec::new(), unclaimed_index: Vec::new(), player_attack_list: Vec::new(), target_attack_list: Vec::new(), width: 0 }
+    }
+
+    /// Initialize the attack handler
+    pub fn init(&mut self, max_players: usize, width: u32) {
+        self.attacks.clear();
+        self.player_index = vec![vec![HashSet::new(); max_players]; max_players];
+        self.unclaimed_index = vec![None; max_players];
+        self.player_attack_list = vec![HashSet::new(); max_players];
+        self.target_attack_list = vec![HashSet::new(); max_players];
+        self.width = width;
+    }
+
+    /// Schedule an attack on unclaimed territory
+    ///
+    /// If an attack on unclaimed territory already exists for this player,
+    /// the troops are added to it and borders are expanded.
+    #[allow(clippy::too_many_arguments)]
+    pub fn schedule_unclaimed(&mut self, player_id: usize, troops: f32, target_tile: usize, border_tiles: Option<&HashSet<usize>>, territory_manager: &TerritoryManager, border_manager: &BorderManager, turn_number: u64, rng: &DeterministicRng) {
+        // Check if there's already an attack on unclaimed territory
+        if let Some(attack_key) = self.unclaimed_index[player_id] {
+            // Add troops to existing attack
+            self.attacks[attack_key].modify_troops(troops);
+
+            // Add new borders to allow multi-region expansion
+            let borders = border_tiles.unwrap_or_else(|| border_manager.get_border_tiles(player_id));
+            self.attacks[attack_key].add_borders(borders, territory_manager, self.width, rng);
+            return;
+        }
+
+        // Create new attack
+        self.add_unclaimed(player_id, troops, target_tile, border_tiles, territory_manager, border_manager, turn_number, rng);
+    }
+
+    /// Schedule an attack on another player
+    ///
+    /// Handles attack merging (if attacking same target) and counter-attacks
+    /// (opposite direction attacks are resolved first).
+    #[allow(clippy::too_many_arguments)]
+    pub fn schedule_attack(&mut self, player_id: usize, target_id: usize, target_tile: usize, mut troops: f32, border_tiles: Option<&HashSet<usize>>, territory_manager: &TerritoryManager, border_manager: &BorderManager, turn_number: u64, rng: &DeterministicRng) {
+        // Check if there's already an attack on this target
+        if let Some(&attack_key) = self.player_index[player_id][target_id].iter().next() {
+            // Add troops to existing attack
+            self.attacks[attack_key].modify_troops(troops);
+
+            // Add new borders to allow multi-region expansion
+            let borders = border_tiles.unwrap_or_else(|| border_manager.get_border_tiles(player_id));
+            self.attacks[attack_key].add_borders(borders, territory_manager, self.width, rng);
+            return;
+        }
+
+        // Check for counter-attacks (opposite direction) - prevent mutual attacks
+        while !self.player_index[target_id][player_id].is_empty() {
+            let opposite_key = *self.player_index[target_id][player_id].iter().next().unwrap();
+
+            if self.attacks[opposite_key].oppose(troops) {
+                // Counter-attack absorbed the new attack
+                return;
+            }
+
+            // Counter-attack was defeated, deduct its troops from the new attack
+            troops -= self.attacks[opposite_key].get_troops();
+
+            // Remove the defeated counter-attack
+            self.remove_attack(opposite_key);
+        }
+
+        // Create new attack
+        self.add_attack(player_id, target_id, troops, target_tile, border_tiles, territory_manager, border_manager, turn_number, rng);
+    }
+
+    /// Tick all active attacks
+    ///
+    /// Progresses each attack by one turn. Attacks that run out of troops
+    /// or conquerable tiles are removed and their remaining troops are
+    /// returned to the attacking player.
+    pub fn tick(&mut self, players: &mut [Player], territory_manager: &mut TerritoryManager, border_manager: &mut BorderManager, rng: &DeterministicRng) {
+        let _span = tracing::trace_span!("attacks_tick", attack_count = self.attacks.len()).entered();
+
+        let mut attacks_to_remove = Vec::new();
+
+        for (attack_key, attack) in &mut self.attacks {
+            let _ = tracing::trace_span!("tick_attack");
+            let should_continue = attack.tick(players, territory_manager, border_manager, self.width, rng);
+
+            if !should_continue {
+                // Return remaining troops to player
+                let player_id = attack.player_id;
+                let remaining_troops = attack.get_troops();
+                tracing::trace!(player_id, remaining_troops, "Attack completed");
+                players[player_id].add_troops(remaining_troops);
+
+                // Mark attack for removal
+                attacks_to_remove.push(attack_key);
+            }
+        }
+
+        // Remove completed attacks
+        for attack_key in attacks_to_remove {
+            self.remove_attack(attack_key);
+        }
+    }
+
+    /// Handle a tile being added to a player's territory
+    ///
+    /// Notifies all relevant attacks that territory has changed so they can
+    /// update their borders and targets.
+    pub fn handle_territory_add(&mut self, tile: usize, player_id: usize, territory_manager: &TerritoryManager, rng: &DeterministicRng) {
+        // Notify all attacks where this player is the attacker
+        for &attack_key in &self.player_attack_list[player_id] {
+            self.attacks[attack_key].handle_player_tile_add(tile, territory_manager, self.width, rng);
+        }
+
+        // Notify all attacks where this player is the target
+        for &attack_key in &self.target_attack_list[player_id] {
+            self.attacks[attack_key].handle_target_tile_add(tile, territory_manager, self.width, rng);
+        }
+    }
+
+    /// Add an attack on unclaimed territory
+    #[allow(clippy::too_many_arguments)]
+    fn add_unclaimed(&mut self, player_id: usize, troops: f32, target_tile: usize, border_tiles: Option<&HashSet<usize>>, territory_manager: &TerritoryManager, border_manager: &BorderManager, turn_number: u64, rng: &DeterministicRng) {
+        let attack = AttackExecutor::new(AttackConfig { player_id, target_id: None, troops, target_tile, border_tiles, territory_manager, border_manager, width: self.width, turn_number }, rng);
+
+        let attack_key = self.attacks.insert(attack);
+        self.unclaimed_index[player_id] = Some(attack_key);
+        self.player_attack_list[player_id].insert(attack_key);
+    }
+
+    /// Add an attack on a player
+    #[allow(clippy::too_many_arguments)]
+    fn add_attack(&mut self, player_id: usize, target_id: usize, troops: f32, target_tile: usize, border_tiles: Option<&HashSet<usize>>, territory_manager: &TerritoryManager, border_manager: &BorderManager, turn_number: u64, rng: &DeterministicRng) {
+        let attack = AttackExecutor::new(AttackConfig { player_id, target_id: Some(target_id), troops, target_tile, border_tiles, territory_manager, border_manager, width: self.width, turn_number }, rng);
+
+        let attack_key = self.attacks.insert(attack);
+        self.player_index[player_id][target_id].insert(attack_key);
+        self.player_attack_list[player_id].insert(attack_key);
+        self.target_attack_list[target_id].insert(attack_key);
+    }
+
+    /// Get all attacks involving a specific player (as attacker or target)
+    ///
+    /// Returns a list of (attacker_id, target_id, troops, start_turn, is_outgoing)
+    /// sorted by start_turn descending (most recent first)
+    pub fn get_attacks_for_player(&self, player_id: usize) -> Vec<(usize, Option<usize>, f32, u64, bool)> {
+        let mut attacks = Vec::new();
+
+        // Add outgoing attacks (player is attacker)
+        for &attack_key in &self.player_attack_list[player_id] {
+            let attack = &self.attacks[attack_key];
+            attacks.push((
+                attack.player_id,
+                attack.target_id,
+                attack.get_troops(),
+                attack.get_start_turn(),
+                true, // outgoing
+            ));
+        }
+
+        // Add incoming attacks (player is target)
+        for &attack_key in &self.target_attack_list[player_id] {
+            let attack = &self.attacks[attack_key];
+            attacks.push((
+                attack.player_id,
+                attack.target_id,
+                attack.get_troops(),
+                attack.get_start_turn(),
+                false, // incoming
+            ));
+        }
+
+        // Sort by start_turn descending (most recent first)
+        attacks.sort_by(|a, b| b.3.cmp(&a.3));
+        attacks
+    }
+
+    /// Remove an attack and update all indices
+    ///
+    /// With SlotMap, keys remain stable so no index shifting is needed.
+    /// HashSet provides O(1) removal without element shifting.
+    fn remove_attack(&mut self, attack_key: AttackKey) {
+        let attack = &self.attacks[attack_key];
+        let player_id = attack.player_id;
+        let target_id = attack.target_id;
+
+        // Remove from player attack list (O(1))
+        self.player_attack_list[player_id].remove(&attack_key);
+
+        if let Some(target_id) = target_id {
+            // Remove from target attack list (O(1))
+            self.target_attack_list[target_id].remove(&attack_key);
+
+            // Remove from player index (O(1))
+            self.player_index[player_id][target_id].remove(&attack_key);
+        } else {
+            // Remove from unclaimed index
+            self.unclaimed_index[player_id] = None;
+        }
+
+        // Remove attack from slot map - no index shifting needed!
+        self.attacks.remove(attack_key);
+    }
+}

crates/borders-core/src/game/combat/calculator.rs

@@ -0,0 +1,152 @@
+/// Pure combat calculation functions
+///
+/// This module contains all combat mathematics extracted from the attack system.
+/// All functions are pure (no side effects) and deterministic, making them
+/// easy to test, reason about, and modify.
+use crate::game::constants::combat::*;
+use crate::game::player::Player;
+use crate::game::territory_manager::TerritoryManager;
+
+/// Parameters for combat result calculation
+pub struct CombatParams<'a> {
+    pub attacker: &'a Player,
+    pub defender: Option<&'a Player>,
+    pub attacker_troops: f32,
+    pub tile: usize,
+    pub territory_manager: &'a TerritoryManager,
+    pub width: u32,
+}
+
+/// Result of combat calculations for conquering one tile
+#[derive(Debug, Clone, Copy)]
+pub struct CombatResult {
+    /// Troops lost by the attacker
+    pub attacker_loss: f32,
+    /// Troops lost by the defender
+    pub defender_loss: f32,
+    /// How much of the "tiles per tick" budget this conquest consumes
+    pub tiles_per_tick_used: f32,
+}
+
+/// Sigmoid function for smooth scaling curves
+///
+/// Used for empire size balancing to create smooth transitions
+/// rather than hard thresholds.
+pub fn sigmoid(x: f32, decay_rate: f32, midpoint: f32) -> f32 {
+    1.0 / (1.0 + (-(x - midpoint) * decay_rate).exp())
+}
+
+/// Clamp a value between min and max
+pub fn clamp(value: f32, min: f32, max: f32) -> f32 {
+    value.max(min).min(max)
+}
+
+/// Calculate combat result for conquering one tile
+///
+/// This function determines troop losses and conquest cost based on:
+/// - Attacker and defender troop counts and empire sizes
+/// - Terrain properties (currently plains baseline)
+/// - Empire size balancing (prevents snowballing)
+/// - Defense structures (placeholder for future implementation)
+pub fn calculate_combat_result(params: CombatParams) -> CombatResult {
+    if let Some(defender) = params.defender {
+        // Attacking claimed territory
+        let attacker = params.attacker;
+
+        // Base terrain values (plains baseline)
+        let mut mag = BASE_MAG_PLAINS;
+        let mut speed = BASE_SPEED_PLAINS;
+
+        // Defense post check (placeholder - always false for now)
+        let has_defense_post = check_defense_post_nearby(params.tile, defender, params.territory_manager, params.width);
+        if has_defense_post {
+            mag *= DEFENSE_POST_MAG_MULTIPLIER;
+            speed *= DEFENSE_POST_SPEED_MULTIPLIER;
+        }
+
+        // Empire size balancing - prevents snowballing
+        // Large defenders get debuffed, large attackers get penalized
+        let defense_sig = 1.0 - sigmoid(defender.get_territory_size() as f32, DEFENSE_DEBUFF_DECAY_RATE, DEFENSE_DEBUFF_MIDPOINT);
+        let large_defender_speed_debuff = 0.7 + 0.3 * defense_sig;
+        let large_defender_attack_debuff = 0.7 + 0.3 * defense_sig;
+
+        let large_attacker_bonus = if attacker.get_territory_size() > LARGE_EMPIRE_THRESHOLD { (LARGE_EMPIRE_THRESHOLD as f32 / attacker.get_territory_size() as f32).sqrt().powf(0.7) } else { 1.0 };
+
+        let large_attacker_speed_bonus = if attacker.get_territory_size() > LARGE_EMPIRE_THRESHOLD { (LARGE_EMPIRE_THRESHOLD as f32 / attacker.get_territory_size() as f32).powf(0.6) } else { 1.0 };
+
+        // Calculate troop ratio
+        let troop_ratio = clamp(defender.get_troops() / params.attacker_troops.max(1.0), 0.6, 2.0);
+
+        // Final attacker loss
+        let attacker_loss = troop_ratio * mag * 0.8 * large_defender_attack_debuff * large_attacker_bonus;
+
+        // Defender loss (simple: troops per tile)
+        let defender_loss = defender.get_troops() / defender.get_territory_size().max(1) as f32;
+
+        // Tiles per tick cost for this tile
+        let tiles_per_tick_used = clamp(defender.get_troops() / (5.0 * params.attacker_troops.max(1.0)), 0.2, 1.5) * speed * large_defender_speed_debuff * large_attacker_speed_bonus;
+
+        CombatResult { attacker_loss, defender_loss, tiles_per_tick_used }
+    } else {
+        // Attacking unclaimed territory
+        CombatResult {
+            attacker_loss: BASE_MAG_PLAINS / 5.0, // 16.0 for plains
+            defender_loss: 0.0,
+            tiles_per_tick_used: clamp((2000.0 * BASE_SPEED_PLAINS.max(10.0)) / params.attacker_troops.max(1.0), 5.0, 100.0),
+        }
+    }
+}
+
+/// Calculate tiles conquered per tick based on troop ratio and border size
+///
+/// This determines how fast an attack progresses. It's based on:
+/// - The attacker's troop advantage (or disadvantage)
+/// - The size of the attack border
+/// - Random variation for organic-looking expansion
+pub fn calculate_tiles_per_tick(attacker_troops: f32, defender: Option<&Player>, border_size: f32) -> f32 {
+    if let Some(defender) = defender {
+        // Dynamic based on troop ratio
+        let ratio = ((5.0 * attacker_troops) / defender.get_troops().max(1.0)) * 2.0;
+        let clamped_ratio = clamp(ratio, 0.01, 0.5);
+        clamped_ratio * border_size * CLAIMED_TILES_PER_TICK_MULTIPLIER
+    } else {
+        // Fixed rate for unclaimed territory
+        border_size * UNCLAIMED_TILES_PER_TICK_MULTIPLIER
+    }
+}
+
+/// Check if defender has a defense post nearby (placeholder)
+///
+/// This will be implemented when defense structures are added to the game.
+/// For now, always returns false.
+fn check_defense_post_nearby(_tile: usize, _defender: &Player, _territory_manager: &TerritoryManager, _width: u32) -> bool {
+    // Placeholder for future defense post implementation
+    false
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn test_sigmoid_midpoint() {
+        let result = sigmoid(DEFENSE_DEBUFF_MIDPOINT, DEFENSE_DEBUFF_DECAY_RATE, DEFENSE_DEBUFF_MIDPOINT);
+        assert!((result - 0.5).abs() < 0.01, "Sigmoid should be ~0.5 at midpoint");
+    }
+
+    #[test]
+    fn test_clamp() {
+        assert_eq!(clamp(5.0, 0.0, 10.0), 5.0);
+        assert_eq!(clamp(-1.0, 0.0, 10.0), 0.0);
+        assert_eq!(clamp(15.0, 0.0, 10.0), 10.0);
+    }
+
+    #[test]
+    fn test_unclaimed_attack_fixed_losses() {
+        // Unclaimed territory should have fixed attacker loss
+        let result = CombatResult { attacker_loss: BASE_MAG_PLAINS / 5.0, defender_loss: 0.0, tiles_per_tick_used: 10.0 };
+
+        assert_eq!(result.attacker_loss, 16.0);
+        assert_eq!(result.defender_loss, 0.0);
+    }
+}

crates/borders-core/src/game/combat/executor.rs

@@ -0,0 +1,333 @@
+/// Attack execution logic
+///
+/// This module contains the `AttackExecutor` which manages the progression
+/// of a single attack over multiple turns. It handles tile prioritization,
+/// border expansion, and conquest mechanics.
+use std::collections::{BinaryHeap, HashSet};
+
+use rand::Rng;
+
+use super::calculator::{CombatParams, calculate_combat_result, calculate_tiles_per_tick};
+use crate::game::constants::combat::*;
+use crate::game::rng::DeterministicRng;
+use crate::game::utils::for_each_neighbor;
+use crate::game::{TileOwnership, borders::BorderManager, player::Player, territory_manager::TerritoryManager};
+
+/// Priority queue entry for tile conquest
+#[derive(Debug, Clone, Copy, PartialEq, Eq)]
+struct TilePriority {
+    tile: usize,
+    priority: i64, // Lower value = higher priority (conquered sooner)
+}
+
+impl PartialOrd for TilePriority {
+    fn partial_cmp(&self, other: &Self) -> Option<std::cmp::Ordering> {
+        Some(self.cmp(other))
+    }
+}
+
+impl Ord for TilePriority {
+    fn cmp(&self, other: &Self) -> std::cmp::Ordering {
+        other.priority.cmp(&self.priority).then_with(|| self.tile.cmp(&other.tile))
+    }
+}
+
+/// Configuration for creating an AttackExecutor
+pub struct AttackConfig<'a> {
+    pub player_id: usize,
+    pub target_id: Option<usize>,
+    pub troops: f32,
+    pub target_tile: usize,
+    pub border_tiles: Option<&'a HashSet<usize>>,
+    pub territory_manager: &'a TerritoryManager,
+    pub border_manager: &'a BorderManager,
+    pub width: u32,
+    pub turn_number: u64,
+}
+
+/// Executes a single ongoing attack (conquering tiles over time)
+///
+/// An attack progresses over multiple turns, conquering tiles based on:
+/// - Available troops
+/// - Troop ratio vs defender
+/// - Border size and connectivity
+/// - Combat formulas from the calculator module
+///
+/// The executor maintains a priority queue of tiles to conquer and updates
+/// borders as it progresses.
+pub struct AttackExecutor {
+    pub player_id: usize,
+    pub target_id: Option<usize>,
+    troops: f32,
+    border_tiles: HashSet<usize>,
+    priority_queue: BinaryHeap<TilePriority>,
+    start_turn: u64,
+    current_turn: u64,
+    tiles_conquered: u64, // Counter for each tile conquered (for priority calculation)
+}
+
+impl AttackExecutor {
+    /// Create a new attack executor
+    pub fn new(config: AttackConfig, rng: &DeterministicRng) -> Self {
+        let mut executor = Self { player_id: config.player_id, target_id: config.target_id, troops: config.troops, border_tiles: HashSet::new(), priority_queue: BinaryHeap::new(), start_turn: config.turn_number, current_turn: config.turn_number, tiles_conquered: 0 };
+
+        executor.initialize_border(config.border_tiles, config.territory_manager, config.border_manager, config.width, rng);
+
+        executor
+    }
+
+    /// Modify the amount of troops in the attack
+    pub fn modify_troops(&mut self, amount: f32) {
+        self.troops += amount;
+    }
+
+    /// Add new border tiles to the attack, allowing expansion from multiple fronts
+    ///
+    /// This enables multi-region expansion when attacking the same target from different areas
+    pub fn add_borders(&mut self, new_border_tiles: &HashSet<usize>, territory_manager: &TerritoryManager, width: u32, rng: &DeterministicRng) {
+        // Add neighbors from each new border tile
+        let height = territory_manager.len() as u32 / width;
+        for &tile in new_border_tiles {
+            for_each_neighbor(tile, width, height, |neighbor| {
+                let neighbor_is_target = if let Some(target_id) = self.target_id { territory_manager.is_owner(neighbor, target_id) } else { !territory_manager.has_owner(neighbor) && !territory_manager.is_water(neighbor) };
+                if neighbor_is_target && !self.border_tiles.contains(&neighbor) {
+                    self.border_tiles.insert(neighbor);
+                    let priority = self.calculate_tile_priority(neighbor, territory_manager, width, rng);
+                    self.priority_queue.push(TilePriority { tile: neighbor, priority });
+                }
+            });
+        }
+    }
+
+    /// Oppose an attack (counter-attack)
+    ///
+    /// Returns true if the attack continues, false if it was defeated
+    pub fn oppose(&mut self, troop_count: f32) -> bool {
+        if self.troops > troop_count {
+            self.troops -= troop_count;
+            true
+        } else {
+            false
+        }
+    }
+
+    /// Get the amount of troops in the attack
+    pub fn get_troops(&self) -> f32 {
+        self.troops.max(0.0).floor()
+    }
+
+    /// Get the turn this attack started
+    pub fn get_start_turn(&self) -> u64 {
+        self.start_turn
+    }
+
+    /// Tick the attack executor
+    ///
+    /// Returns true if the attack continues, false if it's finished
+    pub fn tick(&mut self, players: &mut [Player], territory_manager: &mut TerritoryManager, border_manager: &mut BorderManager, width: u32, rng: &DeterministicRng) -> bool {
+        let _ = tracing::debug_span!("attack_tick");
+        let _span = tracing::trace_span!("attack_tick", player_id = self.player_id).entered();
+
+        self.current_turn += 1;
+
+        // Calculate how many tiles to conquer this tick
+        let mut tiles_per_tick = self.calculate_tiles_per_tick(players, rng);
+
+        // Process tiles from priority queue
+        while tiles_per_tick > 0.0 {
+            if self.troops < 1.0 {
+                return false;
+            }
+
+            if self.priority_queue.is_empty() {
+                // Refresh border tiles one last time before giving up
+                self.refresh_border(border_manager, territory_manager, width, rng);
+
+                // If still empty after refresh, attack is finished
+                if self.priority_queue.is_empty() {
+                    return false;
+                }
+            }
+
+            let tile_priority = self.priority_queue.pop().unwrap();
+            let tile = tile_priority.tile;
+            self.border_tiles.remove(&tile);
+
+            // Check connectivity first
+            let mut on_border = false;
+            let height = territory_manager.len() as u32 / width;
+            for_each_neighbor(tile, width, height, |neighbor| {
+                if territory_manager.is_owner(neighbor, self.player_id) {
+                    on_border = true;
+                }
+            });
+
+            // Check if tile is still valid target
+            let tile_valid = if let Some(target_id) = self.target_id { territory_manager.is_owner(tile, target_id) } else { !territory_manager.has_owner(tile) && !territory_manager.is_water(tile) };
+
+            // Skip if either check fails
+            if !tile_valid || !on_border {
+                continue;
+            }
+
+            // Add neighbors BEFORE conquering (critical for correct expansion)
+            self.add_neighbors_to_border(tile, territory_manager, width, rng);
+
+            // Calculate losses for this tile
+            let combat_result = calculate_combat_result(CombatParams { attacker: &players[self.player_id], defender: self.target_id.map(|id| &players[id]), attacker_troops: self.troops, tile, territory_manager, width });
+
+            // Check if we still have enough troops to conquer this tile
+            if self.troops < combat_result.attacker_loss {
+                return false;
+            }
+
+            // Apply troop losses
+            self.troops -= combat_result.attacker_loss;
+            if let Some(target_id) = self.target_id {
+                players[target_id].remove_troops(combat_result.defender_loss);
+            }
+
+            // Conquer the tile
+            let previous_owner = territory_manager.conquer(tile, self.player_id);
+
+            // Update player territory sizes
+            let previous_ownership = TileOwnership::from_u16(previous_owner);
+            if let Some(nation_id) = previous_ownership.nation_id() {
+                players[nation_id as usize].remove_tile(tile);
+            }
+            players[self.player_id].add_tile(tile);
+
+            // Increment tiles conquered counter (used for priority calculation)
+            self.tiles_conquered += 1;
+
+            // Decrement tiles per tick counter
+            tiles_per_tick -= combat_result.tiles_per_tick_used;
+        }
+
+        // Check if attack should continue
+        !self.priority_queue.is_empty() && self.troops >= 1.0
+    }
+
+    /// Calculate tiles conquered per tick based on troop ratio and border size
+    fn calculate_tiles_per_tick(&mut self, players: &[Player], rng: &DeterministicRng) -> f32 {
+        // Add random 0-4 to border size
+        // This introduces natural variation in expansion speed
+        let mut context_rng = rng.for_context(self.player_id as u64);
+        let random_border_adjustment = context_rng.random_range(0..BORDER_RANDOM_ADJUSTMENT_MAX) as f32;
+        let border_size = self.border_tiles.len() as f32 + random_border_adjustment;
+
+        let defender = self.target_id.map(|id| &players[id]);
+        calculate_tiles_per_tick(self.troops, defender, border_size)
+    }
+
+    /// Initialize border tiles from player's existing borders
+    fn initialize_border(&mut self, border_tiles: Option<&HashSet<usize>>, territory_manager: &TerritoryManager, border_manager: &BorderManager, width: u32, rng: &DeterministicRng) {
+        let borders = border_tiles.unwrap_or_else(|| border_manager.get_border_tiles(self.player_id));
+
+        // Find all target tiles adjacent to our borders
+        let height = territory_manager.len() as u32 / width;
+        for &tile in borders {
+            for_each_neighbor(tile, width, height, |neighbor| {
+                let neighbor_is_target = if let Some(target_id) = self.target_id { territory_manager.is_owner(neighbor, target_id) } else { !territory_manager.has_owner(neighbor) && !territory_manager.is_water(neighbor) };
+                if neighbor_is_target && !self.border_tiles.contains(&neighbor) {
+                    self.border_tiles.insert(neighbor);
+                    let priority = self.calculate_tile_priority(neighbor, territory_manager, width, rng);
+                    self.priority_queue.push(TilePriority { tile: neighbor, priority });
+                }
+            });
+        }
+    }
+
+    /// Refresh the attack border by re-scanning all player border tiles
+    ///
+    /// This gives the attack one last chance to find conquerable tiles before ending
+    fn refresh_border(&mut self, border_manager: &BorderManager, territory_manager: &TerritoryManager, width: u32, rng: &DeterministicRng) {
+        // Clear existing border and queue
+        self.priority_queue.clear();
+        self.border_tiles.clear();
+
+        // Re-scan all player border tiles to find new targets
+        let player_borders = border_manager.get_border_tiles(self.player_id);
+        let height = territory_manager.len() as u32 / width;
+        for &tile in player_borders {
+            for_each_neighbor(tile, width, height, |neighbor| {
+                let neighbor_is_target = if let Some(target_id) = self.target_id { territory_manager.is_owner(neighbor, target_id) } else { !territory_manager.has_owner(neighbor) && !territory_manager.is_water(neighbor) };
+                if neighbor_is_target && !self.border_tiles.contains(&neighbor) {
+                    self.border_tiles.insert(neighbor);
+                    let priority = self.calculate_tile_priority(neighbor, territory_manager, width, rng);
+                    self.priority_queue.push(TilePriority { tile: neighbor, priority });
+                }
+            });
+        }
+    }
+
+    /// Add neighbors of a newly conquered tile to the border
+    fn add_neighbors_to_border(&mut self, tile: usize, territory_manager: &TerritoryManager, width: u32, rng: &DeterministicRng) {
+        let height = territory_manager.len() as u32 / width;
+        for_each_neighbor(tile, width, height, |neighbor| {
+            let neighbor_is_target = if let Some(target_id) = self.target_id { territory_manager.is_owner(neighbor, target_id) } else { !territory_manager.has_owner(neighbor) && !territory_manager.is_water(neighbor) };
+            if neighbor_is_target && !self.border_tiles.contains(&neighbor) {
+                self.border_tiles.insert(neighbor);
+                let priority = self.calculate_tile_priority(neighbor, territory_manager, width, rng);
+                self.priority_queue.push(TilePriority { tile: neighbor, priority });
+            }
+        });
+    }
+
+    /// Calculate priority for a tile (lower = conquered sooner)
+    ///
+    /// Uses tiles_conquered counter to ensure wave-like expansion
+    fn calculate_tile_priority(&self, tile: usize, territory_manager: &TerritoryManager, width: u32, rng: &DeterministicRng) -> i64 {
+        // Count how many neighbors are owned by attacker
+        let mut num_owned_by_attacker = 0;
+        let height = territory_manager.len() as u32 / width;
+        for_each_neighbor(tile, width, height, |neighbor| {
+            if territory_manager.is_owner(neighbor, self.player_id) {
+                num_owned_by_attacker += 1;
+            }
+        });
+
+        // Terrain magnitude (placeholder - always 1.0 for plains)
+        let terrain_mag = 1.0;
+
+        // Random factor (0-7)
+        let mut tile_rng = rng.for_tile(tile);
+        let random_factor = tile_rng.random_range(0..TILE_PRIORITY_RANDOM_MAX);
+
+        // Priority calculation (lower = higher priority, conquered sooner)
+        // Base calculation: tiles surrounded by more attacker neighbors get LOWER modifier values
+        // Adding tiles_conquered ensures tiles discovered earlier get lower priority values
+        // This creates wave-like expansion: older tiles (lower priority) conquered before newer tiles (higher priority)
+        let base = (random_factor + 10) as f32;
+        let modifier = 1.0 - (num_owned_by_attacker as f32 * 0.5) + (terrain_mag / 2.0);
+        (base * modifier) as i64 + self.tiles_conquered as i64
+    }
+
+    /// Handle the addition of a tile to the player's territory
+    pub fn handle_player_tile_add(&mut self, tile: usize, territory_manager: &TerritoryManager, width: u32, rng: &DeterministicRng) {
+        // When player gains a tile, check its neighbors for new targets
+        self.add_neighbors_to_border(tile, territory_manager, width, rng);
+    }
+
+    /// Handle the addition of a tile to the target's territory
+    pub fn handle_target_tile_add(&mut self, tile: usize, territory_manager: &TerritoryManager, width: u32, rng: &DeterministicRng) {
+        // If target gains a tile that borders our territory, add it to attack
+        if Self::check_borders_tile(tile, self.player_id, territory_manager, width) && !self.border_tiles.contains(&tile) {
+            self.border_tiles.insert(tile);
+            let priority = self.calculate_tile_priority(tile, territory_manager, width, rng);
+            self.priority_queue.push(TilePriority { tile, priority });
+        }
+    }
+
+    /// Check if a tile borders the player's territory
+    fn check_borders_tile(tile: usize, player_id: usize, territory_manager: &TerritoryManager, width: u32) -> bool {
+        let height = territory_manager.len() as u32 / width;
+        let mut has_border = false;
+        for_each_neighbor(tile, width, height, |neighbor| {
+            if territory_manager.is_owner(neighbor, player_id) {
+                has_border = true;
+            }
+        });
+        has_border
+    }
+}

crates/borders-core/src/game/combat/mod.rs

@@ -0,0 +1,7 @@
+pub mod active;
+pub mod calculator;
+pub mod executor;
+
+pub use active::*;
+pub use calculator::*;
+pub use executor::*;

crates/borders-core/src/game/connectivity.rs

@@ -0,0 +1,155 @@
+use crate::game::TileOwnership;
+use crate::game::terrain::TerrainData;
+use std::collections::VecDeque;
+
+/// Check if a target tile's region connects to any of the player's tiles
+/// Uses flood-fill through tiles matching the target's ownership
+/// Returns true if connected (normal attack), false if disconnected (ship needed)
+pub fn is_connected_to_player(territory: &[u16], target_tile: usize, player_id: u16, width: usize, height: usize) -> bool {
+    let target_ownership = TileOwnership::from_u16(territory[target_tile]);
+
+    // Can't connect to water
+    if target_ownership.is_water() {
+        return false;
+    }
+
+    // If target is owned by player, it's already connected
+    if target_ownership.is_owned_by(player_id) {
+        return true;
+    }
+
+    // Flood-fill from target through tiles with same ownership
+    let mut queue = VecDeque::new();
+    let mut visited = vec![false; width * height];
+
+    queue.push_back(target_tile);
+    visited[target_tile] = true;
+
+    let directions = [(0, -1), (1, 0), (0, 1), (-1, 0)]; // Cardinal directions only
+
+    while let Some(current) = queue.pop_front() {
+        let x = current % width;
+        let y = current / width;
+
+        // Check all 4 neighbors
+        for (dx, dy) in directions {
+            let nx = x as i32 + dx;
+            let ny = y as i32 + dy;
+
+            // Check bounds
+            if nx < 0 || ny < 0 || nx >= width as i32 || ny >= height as i32 {
+                continue;
+            }
+
+            let neighbor_idx = nx as usize + ny as usize * width;
+
+            // Skip if already visited
+            if visited[neighbor_idx] {
+                continue;
+            }
+
+            let neighbor_ownership = TileOwnership::from_u16(territory[neighbor_idx]);
+
+            // Check if we found a player tile - SUCCESS!
+            if neighbor_ownership.is_owned_by(player_id) {
+                return true;
+            }
+
+            // Only continue through tiles matching target's ownership
+            if neighbor_ownership == target_ownership {
+                visited[neighbor_idx] = true;
+                queue.push_back(neighbor_idx);
+            }
+        }
+    }
+
+    // Exhausted search without finding player tile
+    false
+}
+
+/// Find the nearest coastal tile in a region by flood-filling from target
+/// Only expands through tiles matching the target's ownership
+/// Returns coastal tile index if found
+pub fn find_coastal_tile_in_region(territory: &[u16], terrain: &TerrainData, target_tile: usize, width: usize, height: usize) -> Option<usize> {
+    let target_ownership = TileOwnership::from_u16(territory[target_tile]);
+
+    // Can't find coastal tile in water
+    if target_ownership.is_water() {
+        return None;
+    }
+
+    // Check if target itself is coastal
+    if is_coastal_tile(terrain, target_tile, width, height) {
+        return Some(target_tile);
+    }
+
+    // BFS from target through same-ownership tiles
+    let mut queue = VecDeque::new();
+    let mut visited = vec![false; width * height];
+
+    queue.push_back(target_tile);
+    visited[target_tile] = true;
+
+    let directions = [(0, -1), (1, 0), (0, 1), (-1, 0)];
+
+    while let Some(current) = queue.pop_front() {
+        let x = current % width;
+        let y = current / width;
+
+        for (dx, dy) in directions {
+            let nx = x as i32 + dx;
+            let ny = y as i32 + dy;
+
+            if nx < 0 || ny < 0 || nx >= width as i32 || ny >= height as i32 {
+                continue;
+            }
+
+            let neighbor_idx = nx as usize + ny as usize * width;
+
+            if visited[neighbor_idx] {
+                continue;
+            }
+
+            let neighbor_ownership = TileOwnership::from_u16(territory[neighbor_idx]);
+
+            // Only expand through matching ownership
+            if neighbor_ownership == target_ownership {
+                visited[neighbor_idx] = true;
+
+                // Check if this tile is coastal
+                if is_coastal_tile(terrain, neighbor_idx, width, height) {
+                    return Some(neighbor_idx);
+                }
+
+                queue.push_back(neighbor_idx);
+            }
+        }
+    }
+
+    None
+}
+
+/// Check if a tile is coastal (land tile adjacent to water)
+fn is_coastal_tile(terrain: &TerrainData, tile: usize, width: usize, height: usize) -> bool {
+    let x = tile % width;
+    let y = tile / width;
+
+    // Must be land tile
+    if terrain.is_navigable((x as u32, y as u32)) {
+        return false;
+    }
+
+    // Check if any neighbor is water (4-directional)
+    let directions = [(0, -1), (1, 0), (0, 1), (-1, 0)];
+
+    for (dx, dy) in directions {
+        let nx = x as i32 + dx;
+        let ny = y as i32 + dy;
+
+        if nx >= 0 && ny >= 0 && nx < width as i32 && ny < height as i32 && terrain.is_navigable((nx as u32, ny as u32)) {
+            return true;
+        }
+    }
+
+    false
+}

crates/borders-core/src/game/constants.rs

@@ -0,0 +1,49 @@
+/// Game constants organized by domain
+///
+/// This module centralizes all game balance constants that were previously
+/// scattered across multiple files. Constants are grouped by gameplay domain
+/// for easy discovery and tuning.
+pub mod combat {
+    /// Empire size balancing - prevents snowballing by large empires
+    /// Defense effectiveness decreases as empire grows beyond this threshold
+    pub const DEFENSE_DEBUFF_MIDPOINT: f32 = 150_000.0;
+
+    /// Rate of defense effectiveness decay for large empires
+    /// Uses natural log decay for smooth scaling
+    pub const DEFENSE_DEBUFF_DECAY_RATE: f32 = std::f32::consts::LN_2 / 50_000.0;
+
+    /// Base terrain magnitude cost for plains (baseline terrain)
+    /// Determines troop losses when conquering a tile
+    pub const BASE_MAG_PLAINS: f32 = 80.0;
+
+    /// Base terrain speed for plains (baseline terrain)
+    /// Affects how many tiles can be conquered per tick
+    pub const BASE_SPEED_PLAINS: f32 = 16.5;
+
+    /// Maximum random adjustment to border size when calculating expansion speed
+    /// Introduces natural variation in attack progression (0-4 range)
+    pub const BORDER_RANDOM_ADJUSTMENT_MAX: u32 = 5;
+
+    /// Multiplier for tiles conquered per tick when attacking unclaimed territory
+    pub const UNCLAIMED_TILES_PER_TICK_MULTIPLIER: f32 = 2.0;
+
+    /// Multiplier for tiles conquered per tick when attacking claimed territory
+    pub const CLAIMED_TILES_PER_TICK_MULTIPLIER: f32 = 3.0;
+
+    /// Large empire threshold for attack penalties (>100k tiles)
+    pub const LARGE_EMPIRE_THRESHOLD: usize = 100_000;
+
+    /// Random factor range for tile priority calculation (0-7)
+    pub const TILE_PRIORITY_RANDOM_MAX: u32 = 8;
+
+    /// Defense post magnitude multiplier (when implemented)
+    pub const DEFENSE_POST_MAG_MULTIPLIER: f32 = 5.0;
+
+    /// Defense post speed multiplier (when implemented)
+    pub const DEFENSE_POST_SPEED_MULTIPLIER: f32 = 3.0;
+}
+
+pub mod spawning {
+    /// Radius of tiles claimed around spawn point (creates 5x5 square)
+    pub const SPAWN_RADIUS: i32 = 2;
+}

crates/borders-core/src/game/game_instance.rs

@@ -0,0 +1,420 @@
+use crate::game::action::GameAction;
+use crate::game::borders::BorderManager;
+use crate::game::bot::BotManager;
+use crate::game::combat::ActiveAttacks;
+use crate::game::player_manager::PlayerManager;
+use crate::game::rng::DeterministicRng;
+use crate::game::ships::ShipManager;
+use crate::game::terrain::TerrainData;
+use crate::game::territory_manager::TerritoryManager;
+use crate::networking::{Intent, Turn};
+use bevy_ecs::prelude::*;
+use std::collections::HashSet;
+use std::sync::Arc;
+
+/// Troop count specification for attacks
+enum TroopCount {
+    /// Use a ratio of the player's current troops (0.0-1.0)
+    Ratio(f32),
+    /// Use an absolute troop count
+    Absolute(u32),
+}
+
+/// Game state resource - DETERMINISTIC, SHARED across ALL clients
+///
+/// **Important: This is GLOBAL/SHARED state that must be identical on all clients!**
+///
+/// This resource contains the authoritative game state that:
+/// - Is identical across all clients (server, players, spectators)
+/// - Processes turns deterministically (same input → same output)
+/// - Is used for hash validation and network synchronization
+/// - Continues running even when individual players are eliminated
+///
+/// What belongs here:
+/// - Territory ownership, player stats, attacks, resources
+/// - Turn number, RNG seed (for determinism)
+/// - Any state that affects gameplay or must be validated
+///
+/// What does NOT belong here:
+/// - Client-specific UI state (use LocalPlayerContext)
+/// - Individual player outcomes like Victory/Defeat (use LocalPlayerContext)
+/// - Rendering preferences, camera position, etc. (use local resources)
+///
+/// The game never "stops" based on a single player's outcome - it continues
+/// until a global end condition is met (e.g., all players eliminated, turn limit).
+#[derive(Resource)]
+pub struct GameInstance {
+    pub player_manager: PlayerManager,
+    pub territory_manager: TerritoryManager,
+    pub active_attacks: ActiveAttacks,
+    pub border_manager: BorderManager,
+    pub bot_manager: BotManager,
+    pub ship_manager: ShipManager,
+    pub terrain: Arc<TerrainData>,
+    pub rng: DeterministicRng,
+    pub turn_number: u64,
+    /// Cached set of all coastal tile indices (precomputed once, never changes)
+    /// A coastal tile is a land tile adjacent to water
+    pub coastal_tiles: HashSet<usize>,
+}
+
+impl GameInstance {
+    #[allow(clippy::too_many_arguments)]
+    pub fn new(player_manager: PlayerManager, territory_manager: TerritoryManager, active_attacks: ActiveAttacks, border_manager: BorderManager, bot_manager: BotManager, ship_manager: ShipManager, terrain: Arc<TerrainData>, rng_seed: u64) -> Self {
+        // Precompute coastal tiles (land tiles adjacent to water)
+        let width = territory_manager.width() as usize;
+        let height = territory_manager.height() as usize;
+        let coastal_tiles = Self::compute_coastal_tiles(&terrain, width, height);
+
+        Self { player_manager, territory_manager, active_attacks, border_manager, bot_manager, ship_manager, terrain, rng: DeterministicRng::new(rng_seed), turn_number: 0, coastal_tiles }
+    }
+
+    /// Compute all coastal tile indices (land tiles adjacent to water)
+    /// This is called once at initialization and cached
+    fn compute_coastal_tiles(terrain: &TerrainData, width: usize, height: usize) -> HashSet<usize> {
+        let mut coastal_tiles = HashSet::new();
+        let directions = [(0, -1), (1, 0), (0, 1), (-1, 0)];
+
+        for y in 0..height {
+            for x in 0..width {
+                let tile_idx = x + y * width;
+
+                // Skip water tiles
+                if terrain.is_navigable((x as u32, y as u32)) {
+                    continue;
+                }
+
+                // Check if any neighbor is water (4-directional)
+                for (dx, dy) in directions {
+                    let nx = x as i32 + dx;
+                    let ny = y as i32 + dy;
+
+                    if nx >= 0 && ny >= 0 && nx < width as i32 && ny < height as i32 && terrain.is_navigable((nx as u32, ny as u32)) {
+                        coastal_tiles.insert(tile_idx);
+                        break;
+                    }
+                }
+            }
+        }
+
+        coastal_tiles
+    }
+
+    pub fn execute_turn(&mut self, turn: &Turn) {
+        let _span = tracing::trace_span!("execute_turn", turn_number = self.turn_number, intent_count = turn.intents.len()).entered();
+
+        // Update RNG for this turn
+        self.rng.update_turn(self.turn_number);
+
+        // PHASE 1: Process bot actions (deterministic, based on turn N-1 state)
+        let bot_player_ids = self.bot_manager.bot_player_ids().to_vec();
+        for (bot_index, &player_id) in bot_player_ids.iter().enumerate() {
+            if let Some(player) = self.player_manager.get_player(player_id) {
+                if !player.is_alive() {
+                    continue;
+                }
+
+                if let Some(action) = self.bot_manager.calculate_action(bot_index, self.turn_number, player, &self.territory_manager, &self.border_manager, self.rng.turn_number()) {
+                    tracing::trace!(bot_index, player_id, "Bot action executed");
+                    self.apply_action(action);
+                }
+            }
+        }
+
+        // PHASE 2: Process player intents (from network)
+        for intent in &turn.intents {
+            match intent {
+                Intent::Action(action) => {
+                    self.apply_action(action.clone());
+                }
+                Intent::SetSpawn { .. } => {
+                    // SetSpawn intents should not appear in Turn messages
+                    // They are only valid during spawn phase and handled separately
+                    // If we see one here, it's likely a bug or late arrival - ignore it
+                }
+            }
+        }
+
+        // PHASE 3: Update ships and process arrivals
+        let ship_arrivals = self.ship_manager.update_ships();
+        for (owner_id, target_tile, troops) in ship_arrivals {
+            tracing::debug!(owner_id, target_tile, troops, "Ship arrived at destination, establishing beachhead");
+
+            let player_id = owner_id as usize;
+            let target_tile_usize = target_tile;
+
+            // Step 1: Force-claim the landing tile as beachhead
+            let previous_owner = self.territory_manager.conquer(target_tile_usize, player_id);
+
+            // Border updates now handled by update_player_borders_system (batched at end of turn)
+
+            // Step 2: Update player stats
+            let previous_ownership = crate::game::TileOwnership::from_u16(previous_owner);
+            if let Some(nation_id) = previous_ownership.nation_id()
+                && let Some(prev_owner) = self.player_manager.get_player_mut(nation_id as usize)
+            {
+                prev_owner.remove_tile(target_tile_usize);
+            }
+            if let Some(player) = self.player_manager.get_player_mut(player_id) {
+                player.add_tile(target_tile_usize);
+            }
+
+            // Step 4: Notify active attacks of territory change
+            self.active_attacks.handle_territory_add(target_tile_usize, player_id, &self.territory_manager, &self.rng);
+
+            // Step 5: Create attack from beachhead to expand
+            // Note: Do NOT add troops back - they were deducted at ship launch
+            if let Some(player) = self.player_manager.get_player_mut(player_id) {
+                let _ = player;
+
+                // Find tiles adjacent to the beachhead
+                let width = self.territory_manager.width() as usize;
+                let height = self.territory_manager.height() as usize;
+                let beachhead_x = target_tile_usize % width;
+                let beachhead_y = target_tile_usize / width;
+
+                let directions = [(0, -1), (1, 0), (0, 1), (-1, 0)];
+                let mut adjacent_tiles = Vec::new();
+
+                for (dx, dy) in directions {
+                    let nx = beachhead_x as i32 + dx;
+                    let ny = beachhead_y as i32 + dy;
+
+                    if nx >= 0 && ny >= 0 && (nx as usize) < width && (ny as usize) < height {
+                        let neighbor_idx = nx as usize + ny as usize * width;
+                        adjacent_tiles.push(neighbor_idx);
+                    }
+                }
+
+                // Find valid attack targets (not water, not our own tiles)
+                let valid_targets: Vec<usize> = adjacent_tiles.iter().filter(|&&tile| !self.territory_manager.is_water(tile) && self.territory_manager.get_owner(tile) as usize != player_id).copied().collect();
+
+                // Pick a deterministic random target from valid targets
+                if !valid_targets.is_empty() {
+                    // Deterministic random selection using turn number and beachhead position
+                    let seed = self.turn_number.wrapping_mul(31).wrapping_add(target_tile_usize as u64);
+                    let index = (seed % valid_targets.len() as u64) as usize;
+                    let attack_target = valid_targets[index];
+
+                    // Create a beachhead border set containing just this tile for the attack
+                    let beachhead_borders: HashSet<usize> = std::iter::once(target_tile_usize).collect();
+
+                    // Use the ship's troops for the attack (already deducted at launch)
+                    self.handle_attack_internal(
+                        owner_id,
+                        attack_target as u32,
+                        TroopCount::Absolute(troops),
+                        false, // Don't deduct - troops were already deducted at ship launch
+                        Some(&beachhead_borders),
+                    );
+                } else {
+                    tracing::debug!(player_id, target_tile_usize, "Ship landed but no valid attack targets found (all adjacent tiles are water or owned)");
+                }
+            }
+        }
+
+        // PHASE 4: Tick game systems (attacks, etc.)
+        // Note: Income is processed by process_player_income_system at 10 TPS (before this executes)
+
+        self.active_attacks.tick(self.player_manager.get_players_mut(), &mut self.territory_manager, &mut self.border_manager, &self.rng);
+
+        self.turn_number += 1;
+    }
+
+    /// Apply a game action (used by both bots and player intents)
+    pub fn apply_action(&mut self, action: GameAction) {
+        match action {
+            GameAction::Spawn { player_id, tile_index } => {
+                self.handle_spawn(player_id, tile_index);
+            }
+            GameAction::Attack { player_id, target_tile, troops_ratio } => {
+                self.handle_attack(player_id, target_tile, troops_ratio);
+            }
+            GameAction::LaunchShip { player_id, target_tile, troops_percent } => {
+                self.handle_launch_ship(player_id, target_tile, troops_percent);
+            }
+        }
+    }
+
+    pub fn handle_spawn(&mut self, player_id: u16, tile_index: u32) {
+        let player_id = player_id as usize;
+        let width = self.territory_manager.width();
+        let height = self.territory_manager.height();
+        let tile = tile_index as usize;
+
+        if self.territory_manager.has_owner(tile) || self.territory_manager.is_water(tile) {
+            tracing::debug!(player_id, tile, "Spawn on occupied/water tile ignored");
+            return;
+        }
+
+        let spawn_x = tile as u32 % width;
+        let spawn_y = tile as u32 / width;
+
+        let mut changed: HashSet<usize> = HashSet::new();
+        for dy in -2..=2 {
+            for dx in -2..=2 {
+                let x = (spawn_x as i32 + dx).clamp(0, width as i32 - 1) as u32;
+                let y = (spawn_y as i32 + dy).clamp(0, height as i32 - 1) as u32;
+                let idx = (x + y * width) as usize;
+                if !self.territory_manager.has_owner(idx) && !self.territory_manager.is_water(idx) {
+                    self.territory_manager.conquer(idx, player_id);
+                    changed.insert(idx);
+                }
+            }
+        }
+
+        if !changed.is_empty() {
+            // Border updates now handled by update_player_borders_system (batched at end of turn)
+
+            // Update player stats
+            if let Some(player) = self.player_manager.get_player_mut(player_id) {
+                for &t in &changed {
+                    player.add_tile(t);
+                }
+            }
+            // Notify active attacks that territory changed
+            for &t in &changed {
+                self.active_attacks.handle_territory_add(t, player_id, &self.territory_manager, &self.rng);
+            }
+        }
+    }
+
+    pub fn handle_attack(&mut self, player_id: u16, target_tile: u32, troops_ratio: f32) {
+        self.handle_attack_internal(player_id, target_tile, TroopCount::Ratio(troops_ratio), true, None);
+    }
+
+    /// Handle attack with specific border tiles and troop allocation
+    fn handle_attack_internal(&mut self, player_id: u16, target_tile: u32, troop_count: TroopCount, deduct_from_player: bool, border_tiles: Option<&HashSet<usize>>) {
+        let player_id = player_id as usize;
+        let target_tile = target_tile as usize;
+
+        let target_owner = self.territory_manager.get_owner(target_tile);
+
+        if target_owner as usize == player_id {
+            tracing::debug!(player_id, target_tile, "Attack on own tile ignored");
+            return; // Can't attack self
+        }
+
+        let troops = match troop_count {
+            TroopCount::Ratio(ratio) => {
+                if let Some(player) = self.player_manager.get_player(player_id) {
+                    player.get_troops() * ratio
+                } else {
+                    return;
+                }
+            }
+            TroopCount::Absolute(count) => count as f32,
+        };
+
+        // Deduct troops from the player's pool when creating the attack (if requested)
+        if deduct_from_player {
+            if let Some(player) = self.player_manager.get_player_mut(player_id) {
+                player.remove_troops(troops);
+            } else {
+                return;
+            }
+        }
+
+        let border_tiles_to_use = border_tiles.or_else(|| Some(self.border_manager.get_border_tiles(player_id)));
+
+        use crate::game::TileOwnership;
+        if TileOwnership::from_u16(target_owner).is_unclaimed() {
+            if self.player_manager.get_player(player_id).is_some() {
+                self.active_attacks.schedule_unclaimed(player_id, troops, target_tile, border_tiles_to_use, &self.territory_manager, &self.border_manager, self.turn_number, &self.rng);
+            }
+        } else if self.player_manager.get_player(target_owner as usize).is_some() && self.player_manager.get_player(player_id).is_some() {
+            self.active_attacks.schedule_attack(player_id, target_owner as usize, target_tile, troops, border_tiles_to_use, &self.territory_manager, &self.border_manager, self.turn_number, &self.rng);
+        }
+    }
+
+    pub fn handle_launch_ship(&mut self, player_id: u16, target_tile: u32, troops_percent: u32) {
+        use crate::game::ships::{SHIP_TROOP_PERCENT, ship_pathfinding};
+
+        let player_id_usize = player_id as usize;
+        let target_tile_usize = target_tile as usize;
+
+        // Check if player exists and has troops
+        let player_troops = if let Some(player) = self.player_manager.get_player(player_id_usize) {
+            if !player.is_alive() {
+                tracing::debug!(player_id, "Dead player cannot launch ships");
+                return;
+            }
+            player.get_troops()
+        } else {
+            tracing::debug!(player_id, "Player not found");
+            return;
+        };
+
+        if player_troops <= 0.0 {
+            tracing::debug!(player_id, "Player has no troops to launch ship");
+            return;
+        }
+
+        // Calculate troop count: use provided percentage, or default to 20% if 0
+        let troops_to_send = if troops_percent > 0 {
+            // Clamp to reasonable range (1-100%)
+            let clamped = troops_percent.clamp(1, 100);
+            let calculated = (player_troops * (clamped as f32 / 100.0)).floor() as u32;
+            tracing::debug!(player_id, player_troops, troops_percent = clamped, troops_to_send = calculated, "Ship launch troop calculation");
+            calculated
+        } else {
+            // Default: 20% of troops
+            let calculated = (player_troops * SHIP_TROOP_PERCENT).floor() as u32;
+            tracing::debug!(player_id, player_troops, default_percent = SHIP_TROOP_PERCENT, troops_to_send = calculated, "Ship launch troop calculation (default)");
+            calculated
+        };
+        if troops_to_send == 0 {
+            tracing::debug!(player_id, "Not enough troops to launch ship");
+            return;
+        }
+
+        let width = self.territory_manager.width() as usize;
+        let height = self.territory_manager.height() as usize;
+
+        // Find target's nearest coastal tile
+        let target_coastal_tile = crate::game::connectivity::find_coastal_tile_in_region(self.territory_manager.as_u16_slice(), &self.terrain, target_tile_usize, width, height);
+
+        let target_coastal_tile = match target_coastal_tile {
+            Some(tile) => tile,
+            None => {
+                tracing::debug!(player_id, target_tile, "No coastal tile found in target region");
+                return;
+            }
+        };
+
+        // Find player's nearest coastal tile
+        let player_border_tiles = self.border_manager.get_border_tiles(player_id_usize);
+        let launch_tile = ShipManager::find_nearest_player_coastal_tile(&self.coastal_tiles, player_border_tiles, target_coastal_tile, width);
+
+        let launch_tile = match launch_tile {
+            Some(tile) => tile,
+            None => {
+                tracing::debug!(player_id, target_tile, "Player has no coastal tiles to launch from");
+                return;
+            }
+        };
+
+        // Calculate water path from launch tile to target coastal tile
+        let path = ship_pathfinding::find_water_path(&self.terrain, launch_tile, target_coastal_tile, crate::game::ships::SHIP_MAX_PATH_LENGTH);
+
+        let path = match path {
+            Some(p) => p, // Use full A* path for accurate frontend interpolation
+            None => {
+                tracing::debug!(player_id, target_tile, launch_tile, "No water path found");
+                return;
+            }
+        };
+
+        // Launch the ship
+        if self.ship_manager.launch_ship(player_id, troops_to_send, path, self.turn_number).is_some() {
+            // Deduct troops from player
+            if let Some(player) = self.player_manager.get_player_mut(player_id_usize) {
+                player.remove_troops(troops_to_send as f32);
+            }
+
+            tracing::debug!(player_id, target_tile, troops_to_send, launch_tile, "Ship launched successfully");
+        } else {
+            tracing::debug!(player_id, "Failed to launch ship (likely at ship limit)");
+        }
+    }
+}

crates/borders-core/src/game/income.rs

@@ -0,0 +1,52 @@
+use bevy_ecs::prelude::*;
+use tracing::trace;
+
+use crate::game::{BorderTiles, BotPlayer, CurrentTurn, GameInstance, PlayerId, TerritorySize, Troops};
+
+/// Process player income at 10 TPS (once per turn)
+/// Only runs when turn_is_ready() condition is true
+///
+/// Uses Option<&BotPlayer> to distinguish bot vs human players:
+/// - Some(&BotPlayer) = bot player (60% income, 33% max troops)
+/// - None = human player (100% income, 100% max troops)
+///
+/// On first run, this system also registers player entities if they haven't been registered yet
+pub fn process_player_income_system(current_turn: Res<CurrentTurn>, mut commands: Commands, mut game_instance: ResMut<GameInstance>, query: Query<(Entity, Option<&BotPlayer>)>) {
+    // Check if entities need to be registered (first run)
+    let needs_registration = {
+        let player_manager = &game_instance.player_manager;
+        player_manager.get_players().first().is_some_and(|p| p.entity.is_none())
+    };
+
+    if needs_registration {
+        // Register player entities on first run
+        let bot_player_ids: Vec<usize> = game_instance.bot_manager.bot_player_ids().to_vec();
+
+        for player in game_instance.player_manager.get_players_mut() {
+            let is_bot = bot_player_ids.contains(&player.id);
+
+            let entity = if is_bot { commands.spawn((BotPlayer, PlayerId(player.id as u16), BorderTiles::default(), Troops(player.get_troops()), TerritorySize(player.get_territory_size()))).id() } else { commands.spawn((PlayerId(player.id as u16), BorderTiles::default(), Troops(player.get_troops()), TerritorySize(player.get_territory_size()))).id() };
+
+            player.entity = Some(entity);
+        }
+
+        return; // Skip income processing on registration frame
+    }
+
+    // Process income for all players
+    let player_manager = &mut game_instance.player_manager;
+
+    for player in player_manager.get_players_mut() {
+        if !player.is_alive() {
+            continue;
+        }
+
+        // Determine if this player is a bot by checking ECS entity
+        let is_bot = player.entity.and_then(|entity| query.get(entity).ok()).and_then(|(_, bot_marker)| bot_marker).is_some();
+
+        // Process income with bot modifier if applicable
+        player.income(is_bot);
+    }
+
+    trace!("Income processed for turn {}", current_turn.turn.turn_number);
+}

crates/borders-core/src/game/input_handlers.rs

@@ -0,0 +1,266 @@
+//! Platform-agnostic input handling systems
+//!
+//! These systems use InputState instead of Bevy's input queries,
+//! making them work across both WASM and desktop platforms with
+//! Pixi.js rendering.
+
+use bevy_ecs::prelude::*;
+use tracing::{debug, info, trace};
+
+use crate::game::{GameAction, LocalPlayerContext, SpawnManager, TileOwnership};
+use crate::networking::{GameView, Intent, IntentEvent};
+use crate::ui::input::{InputState, KeyCode, MouseButton};
+use crate::ui::protocol::CameraCommand;
+
+/// Resource tracking whether spawn phase is active
+#[derive(Resource, Default)]
+pub struct SpawnPhase {
+    pub active: bool,
+}
+
+/// Resource for attack control settings
+#[derive(Resource)]
+pub struct AttackControls {
+    pub attack_ratio: f32,
+}
+
+impl Default for AttackControls {
+    fn default() -> Self {
+        Self { attack_ratio: 0.5 }
+    }
+}
+
+/// Handle placing the human spawn by clicking on valid land
+#[allow(clippy::too_many_arguments)]
+pub fn handle_spawn_click_system(input_state: NonSend<std::sync::Arc<std::sync::Mutex<InputState>>>, spawn_phase: Res<SpawnPhase>, game_view: Option<ResMut<GameView>>, local_context: Option<Res<LocalPlayerContext>>, mut spawn_manager: Option<ResMut<SpawnManager>>, mut spawn_timeout: Option<ResMut<crate::game::SpawnTimeout>>, mut intent_writer: MessageWriter<IntentEvent>, game_instance: Option<Res<crate::game::GameInstance>>) {
+    if !spawn_phase.active {
+        return;
+    }
+
+    let Ok(input) = input_state.lock() else {
+        return;
+    };
+
+    if !input.mouse_just_released(MouseButton::Left) {
+        return;
+    }
+
+    let _span = tracing::trace_span!("spawn_click").entered();
+
+    // Frontend handles camera interaction filtering, but double-check here
+    if input.had_camera_interaction() {
+        trace!("Spawn click ignored - camera interaction detected");
+        return;
+    }
+
+    let Some(game_view) = game_view else {
+        debug!("Spawn click ignored - GameView not ready");
+        return;
+    };
+
+    let Some(local_context) = local_context else {
+        debug!("Spawn click ignored - LocalPlayerContext not ready");
+        return;
+    };
+
+    // Can't spawn if not allowed to send intents
+    if !local_context.can_send_intents {
+        debug!("Spawn click ignored - cannot send intents");
+        return;
+    }
+
+    // Get tile from InputState (set by frontend)
+    let Some(tile_coord) = input.cursor_tile() else {
+        debug!("Spawn click ignored - cursor not over valid tile");
+        return;
+    };
+
+    let tile = tile_coord.to_index(game_view.width);
+
+    let tile_ownership = TileOwnership::from_u16(game_view.get_owner(tile));
+    if tile_ownership.is_owned() || tile_ownership.is_water() {
+        debug!("Spawn click on tile {} ignored - occupied or water", tile);
+        return;
+    }
+
+    // Player has chosen a spawn location - send to server
+    info!("Player {} setting spawn at tile {}", local_context.my_player_id, tile);
+
+    // Check if this is the first spawn (timer not started yet)
+    let is_first_spawn = if let Some(ref spawn_mgr) = spawn_manager { spawn_mgr.get_player_spawns().is_empty() } else { true };
+
+    // Send SetSpawn intent to server (not Action - this won't be in game history)
+    // Server will validate, track, and eventually send Turn(0) when timeout expires
+    intent_writer.write(IntentEvent(Intent::SetSpawn { player_id: local_context.my_player_id as u16, tile_index: tile as u32 }));
+
+    // Start spawn timeout on first spawn (spawn_phase plugin will emit countdown updates)
+    if is_first_spawn && let Some(ref mut timeout) = spawn_timeout {
+        timeout.start();
+        info!("Spawn timeout started ({:.1}s)", timeout.duration_secs);
+    }
+
+    // Update local spawn manager for preview/bot recalculation
+    // Note: This only updates the spawn manager, not the game instance
+    // The actual game state is updated when Turn(0) is processed
+    if let Some(ref mut spawn_mgr) = spawn_manager
+        && let Some(ref game_inst) = game_instance
+    {
+        // Update spawn manager (triggers bot spawn recalculation)
+        spawn_mgr.update_player_spawn(local_context.my_player_id, tile, &game_inst.bot_manager, &game_inst.territory_manager);
+
+        info!("Spawn manager updated with player {} spawn at tile {}", local_context.my_player_id, tile);
+        info!("Total spawns in manager: {}", spawn_mgr.get_all_spawns().len());
+    }
+}
+
+/// Center the camera on the client's spawn (hotkey C)
+pub fn handle_center_camera_system(input_state: NonSend<std::sync::Arc<std::sync::Mutex<InputState>>>, game_view: Option<Res<GameView>>, local_context: Option<Res<LocalPlayerContext>>, mut camera_commands: MessageWriter<CameraCommand>) {
+    let Ok(input) = input_state.lock() else {
+        return;
+    };
+
+    if !input.key_just_pressed(KeyCode::KeyC) {
+        return;
+    }
+
+    let Some(game_view) = game_view else {
+        return; // GameView not ready yet
+    };
+
+    let Some(local_context) = local_context else {
+        return; // LocalPlayerContext not ready yet
+    };
+
+    // Find any owned tile to center on
+    if let Some(tile) = game_view.find_tile_owned_by(local_context.my_player_id as u16) {
+        camera_commands.write(CameraCommand::CenterOnTile { tile_index: tile as u32, animate: true });
+    }
+}
+
+/// After spawn, clicking tiles triggers expansion/attack based on ownership
+/// Automatically detects if a ship is needed for water attacks
+pub fn handle_attack_click_system(input_state: NonSend<std::sync::Arc<std::sync::Mutex<InputState>>>, spawn_phase: Res<SpawnPhase>, game_view: Option<Res<GameView>>, game_instance: Option<Res<crate::game::GameInstance>>, local_context: Option<Res<LocalPlayerContext>>, attack_controls: Res<AttackControls>, mut intent_writer: MessageWriter<IntentEvent>) {
+    if spawn_phase.active {
+        return;
+    }
+
+    let Ok(input) = input_state.lock() else {
+        return;
+    };
+
+    if !input.mouse_just_released(MouseButton::Left) {
+        return;
+    }
+
+    // Frontend handles camera interaction filtering
+    if input.had_camera_interaction() {
+        return;
+    }
+
+    let _span = tracing::trace_span!("attack_click").entered();
+
+    let Some(game_view) = game_view else {
+        return; // GameView not ready yet
+    };
+
+    let Some(game_instance) = game_instance else {
+        return; // GameInstance not ready yet
+    };
+
+    let Some(local_context) = local_context else {
+        return; // LocalPlayerContext not ready yet
+    };
+
+    // Can't attack if not allowed to send intents (defeated/spectating)
+    if !local_context.can_send_intents {
+        return;
+    }
+
+    // Get tile from InputState (set by frontend)
+    let Some(tile_coord) = input.cursor_tile() else {
+        return;
+    };
+
+    let tile = tile_coord.to_index(game_view.width);
+    let owner = game_view.get_owner(tile);
+    let player_id = local_context.my_player_id as u16;
+
+    // Can't attack own tiles
+    if owner == player_id {
+        return;
+    }
+
+    // Check if target is water - ignore water clicks
+    let width = game_view.width as usize;
+    if game_instance.terrain.is_navigable(((tile % width) as u32, (tile / width) as u32)) {
+        return;
+    }
+
+    // Check if target is connected to player's territory
+    let height = game_view.height as usize;
+
+    let is_connected = crate::game::connectivity::is_connected_to_player(game_view.territories.as_ref(), tile, player_id, width, height);
+
+    if is_connected {
+        // Target is connected to player's territory - use normal attack
+        intent_writer.write(IntentEvent(Intent::Action(GameAction::Attack { player_id, target_tile: tile as u32, troops_ratio: attack_controls.attack_ratio })));
+        return;
+    }
+
+    // Target is NOT connected - need to use ship
+    debug!("Target {} not connected to player territory, attempting ship launch", tile);
+
+    // Find target's nearest coastal tile
+    let target_coastal_tile = crate::game::connectivity::find_coastal_tile_in_region(game_view.territories.as_ref(), &game_instance.terrain, tile, width, height);
+
+    let Some(target_coastal_tile) = target_coastal_tile else {
+        debug!("No coastal tile found in target's region for tile {}", tile);
+        return;
+    };
+
+    // Find player's nearest coastal tile
+    let player_border_tiles = game_instance.border_manager.get_border_tiles(player_id as usize);
+    let launch_tile = crate::game::ships::ShipManager::find_nearest_player_coastal_tile(&game_instance.coastal_tiles, player_border_tiles, target_coastal_tile, width);
+
+    let Some(launch_tile) = launch_tile else {
+        debug!("Player has no coastal tiles to launch ship from");
+        return;
+    };
+
+    debug!("Found launch tile {} and target coastal tile {} for target {}", launch_tile, target_coastal_tile, tile);
+
+    // Try to find a water path from launch tile to target coastal tile
+    let path = crate::game::ships::ship_pathfinding::find_water_path(&game_instance.terrain, launch_tile, target_coastal_tile, crate::game::ships::SHIP_MAX_PATH_LENGTH);
+
+    if let Some(_path) = path {
+        // We can reach the target by ship!
+        // Convert attack_ratio (0.0-1.0) to troops_percent (0-100)
+        let troops_percent = (attack_controls.attack_ratio * 100.0) as u32;
+
+        debug!("Launching ship to target {} with {}% troops", tile, troops_percent);
+
+        intent_writer.write(IntentEvent(Intent::Action(GameAction::LaunchShip { player_id, target_tile: tile as u32, troops_percent })));
+    } else {
+        debug!("No water path found from {} to {}", launch_tile, target_coastal_tile);
+    }
+}
+
+/// Adjust attack ratio with keys 1/2
+pub fn handle_attack_ratio_keys_system(input_state: NonSend<std::sync::Arc<std::sync::Mutex<InputState>>>, mut controls: ResMut<AttackControls>) {
+    let Ok(input) = input_state.lock() else {
+        return;
+    };
+
+    let mut changed = false;
+    if input.key_just_pressed(KeyCode::Digit1) {
+        controls.attack_ratio = (controls.attack_ratio - 0.1).max(0.1);
+        changed = true;
+    }
+    if input.key_just_pressed(KeyCode::Digit2) {
+        controls.attack_ratio = (controls.attack_ratio + 0.1).min(1.0);
+        changed = true;
+    }
+    if changed {
+        debug!("Attack ratio changed to {:.1}", controls.attack_ratio);
+    }
+}

crates/borders-core/src/game/lifecycle.rs

@@ -0,0 +1,171 @@
+use bevy_ecs::prelude::*;
+use rand::rngs::StdRng;
+use rand::{Rng, SeedableRng};
+use tracing::{debug, info};
+
+use crate::constants::{BOT_COUNT, SPAWN_TIMEOUT_SECS};
+use crate::game::{ActiveAttacks, BorderManager, BotManager, GameInstance, HSLColor, LocalPlayerContext, Player, PlayerManager, SpawnManager, SpawnPhase, SpawnTimeout, TerritoryManager};
+use crate::networking::{GameView, LocalTurnServerHandle, PlayerView, TurnReceiver};
+use flume::Receiver;
+
+/// Parameters needed to initialize a new game
+pub struct GameInitParams {
+    pub map_width: u32,
+    pub map_height: u32,
+    pub conquerable_tiles: Vec<bool>,
+    pub client_player_id: usize,
+    pub intent_rx: Receiver<crate::networking::Intent>,
+    pub terrain_data: std::sync::Arc<crate::game::terrain::TerrainData>,
+}
+
+/// Initialize all game resources when starting a new game
+/// This should be called by the StartGame command handler
+pub fn initialize_game_resources(commands: &mut Commands, params: GameInitParams) {
+    info!("Initializing game resources (map: {}x{}, player: {})", params.map_width, params.map_height, params.client_player_id);
+
+    // Initialize territory manager
+    let mut territory_manager = TerritoryManager::new(params.map_width, params.map_height);
+    territory_manager.reset(params.map_width, params.map_height, &params.conquerable_tiles);
+    debug!("Territory manager initialized with {} tiles", params.conquerable_tiles.len());
+
+    // Initialize border manager
+    let mut border_manager = BorderManager::new();
+    border_manager.reset(params.map_width, params.map_height, 1 + BOT_COUNT);
+
+    // Initialize active attacks
+    let mut active_attacks = ActiveAttacks::new();
+    active_attacks.init(1 + BOT_COUNT, params.map_width);
+
+    // Initialize bot manager (1 human player + BOT_COUNT bots)
+    let bot_manager = BotManager::new(BOT_COUNT, 1);
+    debug!("BotManager initialized with {} bots", BOT_COUNT);
+
+    // Use a fixed seed for deterministic bot behavior and color generation
+    // In multiplayer, this should come from the server
+    let rng_seed = 0xDEADBEEF;
+
+    // Create RNG for deterministic color generation
+    let mut rng = StdRng::seed_from_u64(rng_seed);
+
+    // Create players: 1 human + BOT_COUNT bots
+    // Player IDs start at 0 (human), then 1, 2, 3... for bots
+    let mut players = Vec::new();
+
+    // Generate random hue offset for color spread
+    let hue_offset = rng.random_range(0.0..360.0);
+
+    // All players (including human) get deterministically generated colors
+    for i in 0..=BOT_COUNT {
+        let is_human = i == 0;
+        let id = i as f32;
+
+        // Use golden angle distribution with random offset for visually distinct colors
+        let hue = (id * 137.5 + hue_offset) % 360.0;
+        let saturation = rng.random_range(0.75..=0.95);
+        let lightness = rng.random_range(0.35..=0.65);
+        let color = HSLColor::new(hue, saturation, lightness);
+
+        if is_human {
+            players.push(Player::new(i, "Player".to_string(), color));
+        } else {
+            players.push(Player::new(i, format!("Bot {}", i), color));
+        }
+    }
+
+    // Initialize player manager
+    // Human player is always ID 0
+    let mut player_manager = PlayerManager::new();
+    let human_player_id = 0;
+    player_manager.init(players, human_player_id);
+    debug!("Player manager initialized with {} players (human: {}, bots: {})", 1 + BOT_COUNT, human_player_id, BOT_COUNT);
+
+    // Create ship manager
+    let ship_manager = crate::game::ships::ShipManager::new();
+
+    // Create game instance (bots won't be spawned until player chooses spawn)
+    let game_instance = GameInstance::new(player_manager, territory_manager, active_attacks, border_manager, bot_manager, ship_manager, params.terrain_data.clone(), rng_seed);
+
+    // Calculate initial bot spawn positions (first pass)
+    // These will be shown to the player, but not applied to game state yet
+    let initial_bot_spawns = game_instance.bot_manager.calculate_initial_spawns(&game_instance.territory_manager, rng_seed);
+
+    debug!("Calculated {} initial bot spawn positions (requested: {})", initial_bot_spawns.len(), BOT_COUNT);
+
+    if initial_bot_spawns.len() < BOT_COUNT {
+        tracing::warn!("Only {} of {} bots were able to spawn - map may be too small or bot count too high", initial_bot_spawns.len(), BOT_COUNT);
+    }
+
+    // Create SpawnManager to track spawn positions during spawn phase
+    let spawn_manager = SpawnManager::new(initial_bot_spawns.clone(), rng_seed, params.map_width, params.map_height);
+    commands.insert_resource(spawn_manager);
+
+    // Initialize GameView with initial game state
+    // Calculate total land tiles once for caching (performance optimization)
+    use std::sync::Arc;
+
+    let total_land_tiles = game_instance.territory_manager.as_slice().iter().filter(|ownership| !ownership.is_water()).count() as u32;
+
+    let game_view = GameView {
+        width: params.map_width,
+        height: params.map_height,
+        territories: Arc::from(game_instance.territory_manager.to_u16_vec().as_slice()),
+        turn_number: 0,
+        total_land_tiles,
+        changed_tiles: Vec::new(), // Empty on initialization
+        players: game_instance.player_manager.get_players().iter().map(|p| PlayerView { id: p.id as u16, color: p.color.to_rgba(), name: p.name.clone(), tile_count: p.get_territory_size() as u32, troops: p.get_troops() as u32, is_alive: p.is_alive() }).collect(),
+        ships: Vec::new(), // No ships at initialization
+    };
+
+    commands.insert_resource(game_instance);
+    commands.insert_resource(game_view);
+    debug!("GameInstance and GameView resources created");
+
+    // Initialize local player context
+    commands.insert_resource(LocalPlayerContext::new(0)); // Human player is ID 0
+    debug!("LocalPlayerContext created for player 0 (human)");
+
+    // Initialize spawn timeout
+    commands.insert_resource(SpawnTimeout::new(SPAWN_TIMEOUT_SECS));
+    debug!("SpawnTimeout initialized ({} seconds)", SPAWN_TIMEOUT_SECS);
+
+    // Initialize turn generation resources
+    let (turn_tx, turn_rx) = flume::unbounded();
+    let server_handle = LocalTurnServerHandle { paused: std::sync::Arc::new(std::sync::atomic::AtomicBool::new(true)), running: std::sync::Arc::new(std::sync::atomic::AtomicBool::new(true)) };
+    commands.insert_resource(server_handle);
+    commands.insert_resource(TurnReceiver { turn_rx });
+    commands.insert_resource(crate::networking::TurnGenerator { turn_number: 0, accumulated_time: 0.0, turn_tx, spawn_config: std::collections::HashMap::new(), spawn_timeout_accumulated: None, game_started: false });
+
+    debug!("Turn generator initialized (paused until player spawn)");
+
+    // Activate spawn phase (SpawnPhasePlugin will emit initial SpawnPhaseUpdate)
+    commands.insert_resource(SpawnPhase { active: true });
+    debug!("Spawn phase activated");
+
+    info!("Game resources initialized successfully - ready to start");
+}
+
+/// Clean up all game resources when quitting a game
+/// This should be called by the QuitGame command handler
+pub fn cleanup_game_resources(world: &mut World) {
+    info!("Cleaning up game resources...");
+
+    // Stop local turn server if running
+    if let Some(server_handle) = world.get_resource::<LocalTurnServerHandle>() {
+        server_handle.stop();
+        world.remove_resource::<LocalTurnServerHandle>();
+    }
+
+    // Remove all game-specific resources
+    world.remove_resource::<GameInstance>();
+    world.remove_resource::<LocalPlayerContext>();
+    world.remove_resource::<TurnReceiver>();
+    world.remove_resource::<SpawnManager>();
+    world.remove_resource::<SpawnTimeout>();
+    world.remove_resource::<crate::networking::GameView>();
+    world.remove_resource::<crate::TerrainData>();
+    world.remove_resource::<crate::networking::TurnGenerator>();
+
+    // Note: SpawnPhase is a permanent resource (init_resource), not removed on quit
+
+    info!("Game resources cleaned up successfully");
+}

crates/borders-core/src/game/local_context.rs

@@ -0,0 +1,71 @@
+use bevy_ecs::prelude::*;
+use serde::{Deserialize, Serialize};
+
+/// Represents the outcome for a specific player (local, not shared)
+#[derive(Debug, Clone, Copy, PartialEq, Eq, Serialize, Deserialize)]
+pub enum PlayerOutcome {
+    /// Player has won the game
+    Victory,
+    /// Player has been eliminated/defeated
+    Defeat,
+}
+
+/// Local player context - CLIENT-SPECIFIC state, NOT part of deterministic game state
+///
+/// **Important: This is LOCAL context, not shared/deterministic state!**
+///
+/// This resource contains information specific to THIS client's perspective:
+/// - Which player ID this client controls
+/// - Whether this player won/lost (irrelevant to other clients)
+/// - Whether this client can send commands or is spectating
+///
+/// This state is NOT synchronized across clients and is NOT part of
+/// GameInstance/GameView which must be identical on all clients for determinism.
+///
+/// In multiplayer:
+/// - Each client has their own LocalPlayerContext with different player IDs
+/// - One client may have `my_outcome = Victory` while others have `Defeat`
+/// - A spectator would have `can_send_intents = false`
+/// - The shared game state (GameInstance) continues running regardless
+#[derive(Resource)]
+pub struct LocalPlayerContext {
+    /// The player ID for this client
+    pub my_player_id: usize,
+
+    /// The outcome for this specific player (if determined)
+    /// None = still playing, Some(Victory/Defeat) = game ended for this player
+    pub my_outcome: Option<PlayerOutcome>,
+
+    /// Whether this client can send intents (false when defeated or spectating)
+    pub can_send_intents: bool,
+}
+
+impl LocalPlayerContext {
+    /// Create a new local player context for the given player ID
+    pub fn new(player_id: usize) -> Self {
+        Self { my_player_id: player_id, my_outcome: None, can_send_intents: true }
+    }
+
+    /// Mark the local player as defeated
+    pub fn mark_defeated(&mut self) {
+        self.my_outcome = Some(PlayerOutcome::Defeat);
+        self.can_send_intents = false;
+    }
+
+    /// Mark the local player as victorious
+    pub fn mark_victorious(&mut self) {
+        self.my_outcome = Some(PlayerOutcome::Victory);
+        // Player can still send intents after victory (to continue playing if desired)
+        // Or set to false if you want to prevent further actions
+    }
+
+    /// Check if the local player is still actively playing
+    pub fn is_playing(&self) -> bool {
+        self.my_outcome.is_none() && self.can_send_intents
+    }
+
+    /// Check if the local player is spectating (defeated but watching)
+    pub fn is_spectating(&self) -> bool {
+        !self.can_send_intents
+    }
+}

crates/borders-core/src/game/mod.rs

@@ -0,0 +1,51 @@
+pub mod action;
+pub mod borders;
+pub mod bot;
+pub mod combat;
+pub mod connectivity;
+pub mod constants;
+pub mod game_instance;
+pub mod income;
+pub mod input_handlers;
+pub mod lifecycle;
+pub mod local_context;
+pub mod outcome;
+pub mod player;
+pub mod player_manager;
+pub mod rng;
+pub mod ships;
+pub mod spawn_manager;
+pub mod spawn_timeout;
+pub mod terrain;
+pub mod territory;
+pub mod territory_manager;
+pub mod tile_ownership;
+pub mod tilemap;
+pub mod tilemap_changes;
+pub mod turn;
+pub mod utils;
+
+pub use action::*;
+pub use borders::{BorderManager, BorderTransitionResult, update_player_borders_system};
+pub use bot::*;
+pub use combat::{ActiveAttacks, AttackConfig, AttackExecutor};
+pub use connectivity::*;
+pub use game_instance::*;
+pub use income::process_player_income_system;
+pub use input_handlers::*;
+pub use lifecycle::*;
+pub use local_context::*;
+pub use outcome::*;
+pub use player::{BorderTiles, BotPlayer, HSLColor, Player, PlayerId, TerritorySize, Troops};
+pub use player_manager::*;
+pub use rng::DeterministicRng;
+pub use ships::*;
+pub use spawn_manager::*;
+pub use spawn_timeout::*;
+pub use terrain::*;
+pub use territory::*;
+pub use territory_manager::*;
+pub use tile_ownership::*;
+pub use tilemap::*;
+pub use tilemap_changes::*;
+pub use turn::{CurrentTurn, turn_is_ready};

crates/borders-core/src/game/outcome.rs

@@ -0,0 +1,82 @@
+use crate::game::local_context::LocalPlayerContext;
+use crate::game::territory_manager::OWNER_WATER;
+use crate::networking::GameView;
+use crate::ui::protocol::{BackendMessage, GameOutcome};
+use bevy_ecs::prelude::*;
+use tracing::info;
+
+/// System that checks if the local player has won or lost
+/// This is a NON-BLOCKING check - the game continues running regardless
+pub fn check_local_player_outcome(mut local_context: ResMut<LocalPlayerContext>, game_view: Res<GameView>, mut backend_messages: MessageWriter<BackendMessage>) {
+    // Don't check if outcome already determined
+    if local_context.my_outcome.is_some() {
+        return;
+    }
+
+    // Don't check outcome until player has spawned
+    // Skip only if player has 0 tiles AND is_alive (hasn't spawned yet)
+    // If player has 0 tiles AND !is_alive, that's a real defeat
+    let my_player_id = local_context.my_player_id as u16;
+    let Some(my_player) = game_view.get_player(my_player_id) else {
+        return;
+    };
+
+    if my_player.tile_count == 0 && my_player.is_alive {
+        // Player hasn't spawned yet - skip outcome check
+        return;
+    }
+
+    // Check defeat condition: I've been eliminated (0 tiles)
+    if !my_player.is_alive {
+        info!("Local player defeated - eliminated (0 tiles)");
+        local_context.mark_defeated();
+        backend_messages.write(BackendMessage::GameEnded { outcome: GameOutcome::Defeat });
+        return;
+    }
+
+    // Calculate total claimable tiles for victory condition checks
+    let total_claimable_tiles = game_view.territories.iter().filter(|&&owner| owner != OWNER_WATER).count();
+
+    const WIN_THRESHOLD: f32 = 0.80;
+
+    if total_claimable_tiles > 0 {
+        let my_tiles = my_player.tile_count as usize;
+        let my_occupation = my_tiles as f32 / total_claimable_tiles as f32;
+
+        // Check if I've won by occupation
+        if my_occupation >= WIN_THRESHOLD {
+            info!("Local player victorious - reached {:.1}% occupation ({}/{} claimable tiles, threshold: {:.0}%)", my_occupation * 100.0, my_tiles, total_claimable_tiles, WIN_THRESHOLD * 100.0);
+            local_context.mark_victorious();
+            backend_messages.write(BackendMessage::GameEnded { outcome: GameOutcome::Victory });
+            return;
+        }
+
+        // Check if any opponent has won by occupation (which means I lost)
+        for player in &game_view.players {
+            if player.id != my_player_id && player.is_alive {
+                let opponent_tiles = player.tile_count as usize;
+                let opponent_occupation = opponent_tiles as f32 / total_claimable_tiles as f32;
+
+                if opponent_occupation >= WIN_THRESHOLD {
+                    info!("Local player defeated - {} reached {:.1}% occupation ({}/{} claimable tiles, threshold: {:.0}%)", player.name, opponent_occupation * 100.0, opponent_tiles, total_claimable_tiles, WIN_THRESHOLD * 100.0);
+                    local_context.mark_defeated();
+                    backend_messages.write(BackendMessage::GameEnded { outcome: GameOutcome::Defeat });
+                    return;
+                }
+            }
+        }
+    }
+
+    // Check victory by eliminating all opponents
+    let all_opponents_dead = game_view
+        .players
+        .iter()
+        .filter(|p| p.id != my_player_id) // Exclude me
+        .all(|p| !p.is_alive);
+
+    if all_opponents_dead && my_player.is_alive {
+        info!("Local player victorious - all opponents eliminated");
+        local_context.mark_victorious();
+        backend_messages.write(BackendMessage::GameEnded { outcome: GameOutcome::Victory });
+    }
+}

crates/borders-core/src/game/player.rs

@@ -0,0 +1,199 @@
+use bevy_ecs::prelude::*;
+use std::collections::HashSet;
+
+/// Marker component to identify bot players
+/// Human players are identified by the ABSENCE of this component
+/// Use Option<&BotPlayer> in queries to handle both types
+#[derive(Component, Debug, Clone, Copy, Default)]
+pub struct BotPlayer;
+
+/// Player ID component for ECS queries
+#[derive(Component, Debug, Clone, Copy)]
+pub struct PlayerId(pub u16);
+
+/// Border tiles component - tiles at the edge of a player's territory
+#[derive(Component, Debug, Clone, Default)]
+pub struct BorderTiles(pub HashSet<usize>);
+
+/// Troops component - current troop count
+#[derive(Component, Debug, Clone, Copy)]
+pub struct Troops(pub f32);
+
+/// Territory size component - number of tiles owned
+#[derive(Component, Debug, Clone, Copy)]
+pub struct TerritorySize(pub usize);
+
+/// HSL Color representation
+#[derive(Debug, Clone, Copy)]
+pub struct HSLColor {
+    pub h: f32, // Hue: 0-360
+    pub s: f32, // Saturation: 0-1
+    pub l: f32, // Lightness: 0-1
+}
+
+impl HSLColor {
+    pub fn new(h: f32, s: f32, l: f32) -> Self {
+        Self { h, s, l }
+    }
+
+    pub fn to_rgba(&self) -> [f32; 4] {
+        let c = (1.0 - (2.0 * self.l - 1.0).abs()) * self.s;
+        let h_prime = self.h / 60.0;
+        let x = c * (1.0 - ((h_prime % 2.0) - 1.0).abs());
+
+        let (r1, g1, b1) = if h_prime < 1.0 {
+            (c, x, 0.0)
+        } else if h_prime < 2.0 {
+            (x, c, 0.0)
+        } else if h_prime < 3.0 {
+            (0.0, c, x)
+        } else if h_prime < 4.0 {
+            (0.0, x, c)
+        } else if h_prime < 5.0 {
+            (x, 0.0, c)
+        } else {
+            (c, 0.0, x)
+        };
+
+        let m = self.l - c / 2.0;
+        [r1 + m, g1 + m, b1 + m, 1.0]
+    }
+
+    pub fn from_rgb(r: u8, g: u8, b: u8) -> Self {
+        let r = r as f32 / 255.0;
+        let g = g as f32 / 255.0;
+        let b = b as f32 / 255.0;
+
+        let max = r.max(g).max(b);
+        let min = r.min(g).min(b);
+        let delta = max - min;
+
+        let l = (max + min) / 2.0;
+
+        if delta == 0.0 {
+            return Self { h: 0.0, s: 0.0, l };
+        }
+
+        let s = if l < 0.5 { delta / (max + min) } else { delta / (2.0 - max - min) };
+
+        let h = if max == r {
+            60.0 * (((g - b) / delta) % 6.0)
+        } else if max == g {
+            60.0 * (((b - r) / delta) + 2.0)
+        } else {
+            60.0 * (((r - g) / delta) + 4.0)
+        };
+
+        let h = if h < 0.0 { h + 360.0 } else { h };
+
+        Self { h, s, l }
+    }
+}
+
+/// Nation in the game (controlled by either human player or bot AI)
+#[derive(Debug, Clone)]
+pub struct Nation {
+    pub id: usize,
+    pub name: String,
+    pub color: HSLColor,
+    troops: f32,
+    territory_size: usize,
+    alive: bool,
+    pub entity: Option<Entity>, // Link to ECS entity
+}
+
+impl Nation {
+    pub fn new(id: usize, name: String, color: HSLColor) -> Self {
+        Self { id, name, color, troops: 2500.0, territory_size: 0, alive: true, entity: None }
+    }
+
+    /// Add a tile to the nation's territory
+    /// WARNING: Call this AFTER updating the territory manager
+    pub fn add_tile(&mut self, _tile: usize) {
+        self.territory_size += 1;
+    }
+
+    /// Remove a tile from the nation's territory
+    /// WARNING: Call this AFTER updating the territory manager
+    pub fn remove_tile(&mut self, _tile: usize) {
+        self.territory_size = self.territory_size.saturating_sub(1);
+        if self.territory_size == 0 {
+            self.alive = false;
+        }
+    }
+
+    /// Calculate maximum troop capacity based on territory size
+    /// 2 * (tiles^0.6 * 1000 + 50000)
+    pub fn calculate_max_troops(&self, is_bot: bool) -> f32 {
+        let base_max = 2.0 * ((self.territory_size as f32).powf(0.6) * 1000.0 + 50_000.0);
+
+        if is_bot {
+            base_max * 0.33 // Bots get 33% max troops
+        } else {
+            base_max
+        }
+    }
+
+    /// Calculate income for this tick
+    pub fn calculate_income(&self, is_bot: bool) -> f32 {
+        let max_troops = self.calculate_max_troops(is_bot);
+
+        // Base income calculation
+        let mut income = 10.0 + (self.troops.powf(0.73) / 4.0);
+
+        // Soft cap as approaching max troops
+        let ratio = 1.0 - (self.troops / max_troops);
+        income *= ratio;
+
+        // Apply bot modifier
+        if is_bot {
+            income * 0.6 // Bots get 60% income
+        } else {
+            income
+        }
+    }
+
+    /// Process one tick worth of income
+    pub fn income(&mut self, is_bot: bool) {
+        let income = self.calculate_income(is_bot);
+        self.add_troops_internal(income, is_bot);
+    }
+
+    /// Internal method to add troops with max cap
+    fn add_troops_internal(&mut self, amount: f32, is_bot: bool) {
+        let max_troops = self.calculate_max_troops(is_bot);
+        self.troops = (self.troops + amount).min(max_troops);
+    }
+
+    /// Get the amount of troops the nation has
+    pub fn get_troops(&self) -> f32 {
+        self.troops
+    }
+
+    /// Add troops to the nation
+    /// Troops will be capped based on territory size using the max troops formula
+    /// For internal use; external callers should use the income system
+    pub fn add_troops(&mut self, amount: f32) {
+        // For external calls (attacks, donations), always use human formula
+        // This ensures consistent behavior for troop transfers
+        self.add_troops_internal(amount, false);
+    }
+
+    /// Remove troops from the nation
+    pub fn remove_troops(&mut self, amount: f32) {
+        self.troops = (self.troops - amount).max(0.0);
+    }
+
+    /// Get the size of the nation's territory (in tiles)
+    pub fn get_territory_size(&self) -> usize {
+        self.territory_size
+    }
+
+    /// Check if the nation is alive
+    pub fn is_alive(&self) -> bool {
+        self.alive
+    }
+}
+
+/// Type alias for backward compatibility during ECS migration
+pub type Player = Nation;

crates/borders-core/src/game/player_manager.rs

@@ -0,0 +1,72 @@
+use crate::game::player::Player;
+
+/// Manages all players in the game
+pub struct PlayerManager {
+    players: Vec<Player>,
+    pub client_player_id: usize,
+    human_count: usize,
+}
+
+impl Default for PlayerManager {
+    fn default() -> Self {
+        Self::new()
+    }
+}
+
+impl PlayerManager {
+    pub fn new() -> Self {
+        Self { players: Vec::new(), client_player_id: 0, human_count: 0 }
+    }
+
+    /// Initialize the player manager
+    pub fn init(&mut self, players: Vec<Player>, client_player_id: usize) {
+        self.players = players;
+        self.client_player_id = client_player_id;
+        self.human_count = 1; // For now, only one human player
+    }
+
+    /// Register a new player
+    pub fn register_player(&mut self, player: Player) {
+        self.players.push(player);
+    }
+
+    /// Get a player by ID
+    pub fn get_player(&self, id: usize) -> Option<&Player> {
+        self.players.get(id)
+    }
+
+    /// Get a mutable player by ID
+    pub fn get_player_mut(&mut self, id: usize) -> Option<&mut Player> {
+        self.players.get_mut(id)
+    }
+
+    /// Get all players
+    pub fn get_players(&self) -> &[Player] {
+        &self.players
+    }
+
+    /// Get all players mutably
+    pub fn get_players_mut(&mut self) -> &mut [Player] {
+        &mut self.players
+    }
+
+    /// Check if a player is a bot
+    pub fn is_bot(&self, player_id: usize) -> bool {
+        player_id >= self.human_count
+    }
+
+    /// Validate a player ID
+    pub fn validate_player(&self, player_id: usize) -> bool {
+        self.players.get(player_id).is_some_and(|p| p.is_alive())
+    }
+
+    /// Get the number of players
+    pub fn player_count(&self) -> usize {
+        self.players.len()
+    }
+
+    /// Get the client player
+    pub fn get_client_player(&self) -> Option<&Player> {
+        self.get_player(self.client_player_id)
+    }
+}

crates/borders-core/src/game/rng.rs

@@ -0,0 +1,121 @@
+use bevy_ecs::prelude::*;
+use rand::SeedableRng;
+use rand::rngs::StdRng;
+
+/// Centralized deterministic RNG resource
+///
+/// This resource provides deterministic random number generation for all game systems.
+/// It is updated at the start of each turn with the current turn number, ensuring that
+/// the same sequence of turns always produces the same random values.
+///
+/// # Determinism Guarantees
+///
+/// - Same turn number + base seed + context → same RNG state
+/// - No stored RNG state in individual systems (prevents desync)
+/// - All randomness flows through this single source of truth
+///
+/// # Usage
+///
+/// Systems should never store RNG state. Instead, request context-specific RNG:
+///
+/// ```rust,ignore
+/// fn my_system(rng: Res<DeterministicRng>) {
+///     let mut player_rng = rng.for_player(player_id);
+///     let random_value = player_rng.gen_range(0..10);
+/// }
+/// ```
+#[derive(Resource)]
+pub struct DeterministicRng {
+    /// Base seed for the entire game (set at game start)
+    base_seed: u64,
+    /// Current turn number (updated each turn)
+    turn_number: u64,
+}
+
+impl DeterministicRng {
+    /// Create a new DeterministicRng with a base seed
+    pub fn new(base_seed: u64) -> Self {
+        Self { base_seed, turn_number: 0 }
+    }
+
+    /// Update the turn number (should be called at start of each turn)
+    pub fn update_turn(&mut self, turn_number: u64) {
+        self.turn_number = turn_number;
+    }
+
+    /// Get the current turn number
+    pub fn turn_number(&self) -> u64 {
+        self.turn_number
+    }
+
+    /// Create an RNG for a specific context within the current turn
+    ///
+    /// The context_id allows different systems/entities to have independent
+    /// random sequences while maintaining determinism.
+    pub fn for_context(&self, context_id: u64) -> StdRng {
+        let seed = self
+            .turn_number
+            .wrapping_mul(997) // Prime multiplier for turn
+            .wrapping_add(self.base_seed)
+            .wrapping_add(context_id.wrapping_mul(1009)); // Prime multiplier for context
+        StdRng::seed_from_u64(seed)
+    }
+
+    /// Get an RNG for a specific player's actions this turn
+    ///
+    /// This is a convenience wrapper around `for_context` for player-specific randomness.
+    pub fn for_player(&self, player_id: usize) -> StdRng {
+        self.for_context(player_id as u64)
+    }
+
+    /// Get an RNG for a specific tile's calculations this turn
+    ///
+    /// Useful for tile-based randomness that should be consistent within a turn.
+    pub fn for_tile(&self, tile_index: usize) -> StdRng {
+        // Use large offset to avoid collision with player IDs
+        self.for_context(1_000_000 + tile_index as u64)
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+    use rand::Rng;
+
+    #[test]
+    fn test_deterministic_same_turn_same_seed() {
+        let rng1 = DeterministicRng::new(12345);
+        let rng2 = DeterministicRng::new(12345);
+
+        let mut player_rng1 = rng1.for_player(0);
+        let mut player_rng2 = rng2.for_player(0);
+
+        assert_eq!(player_rng1.random::<u64>(), player_rng2.random::<u64>());
+    }
+
+    #[test]
+    fn test_deterministic_different_context() {
+        let rng = DeterministicRng::new(12345);
+
+        let mut player0_rng = rng.for_player(0);
+        let mut player1_rng = rng.for_player(1);
+
+        // Different contexts should produce different values
+        assert_ne!(player0_rng.random::<u64>(), player1_rng.random::<u64>());
+    }
+
+    #[test]
+    fn test_turn_update() {
+        let mut rng = DeterministicRng::new(12345);
+
+        let mut turn0_rng = rng.for_player(0);
+        let value_turn0 = turn0_rng.random::<u64>();
+
+        rng.update_turn(1);
+        let mut turn1_rng = rng.for_player(0);
+        let value_turn1 = turn1_rng.random::<u64>();
+
+        // Same player, different turns should produce different values
+        assert_ne!(value_turn0, value_turn1);
+    }
+}

crates/borders-core/src/game/ships/mod.rs

@@ -0,0 +1,12 @@
+pub mod ship_manager;
+pub mod ship_pathfinding;
+pub mod transport_ship;
+
+pub use ship_manager::ShipManager;
+pub use transport_ship::TransportShip;
+
+// Ship-related constants
+pub const MAX_SHIPS_PER_PLAYER: usize = 5;
+pub const SHIP_TICKS_PER_TILE: u32 = 1; // How many ticks to move one tile (1 = fast speed)
+pub const SHIP_MAX_PATH_LENGTH: usize = 1_000_000;
+pub const SHIP_TROOP_PERCENT: f32 = 0.20;

crates/borders-core/src/game/ships/ship_manager.rs

@@ -0,0 +1,158 @@
+use crate::game::ships::transport_ship::TransportShip;
+use crate::game::ships::{MAX_SHIPS_PER_PLAYER, SHIP_MAX_PATH_LENGTH, SHIP_TICKS_PER_TILE};
+use serde::{Deserialize, Serialize};
+use std::collections::HashMap;
+use tracing::debug;
+
+/// Manages all active ships in the game
+#[derive(Debug, Clone, Serialize, Deserialize)]
+pub struct ShipManager {
+    /// All active ships, indexed by ship ID
+    ships: HashMap<u32, TransportShip>,
+
+    /// Track number of ships per player
+    ships_per_player: HashMap<u16, usize>,
+
+    /// Next available ship ID
+    next_ship_id: u32,
+}
+
+impl ShipManager {
+    pub fn new() -> Self {
+        Self { ships: HashMap::new(), ships_per_player: HashMap::new(), next_ship_id: 1 }
+    }
+
+    /// Launch a new transport ship if possible
+    /// Returns Some(ship_id) if successful, None if launch failed
+    pub fn launch_ship(&mut self, owner_id: u16, troops: u32, path: Vec<usize>, launch_tick: u64) -> Option<u32> {
+        // Check if player has reached ship limit
+        let current_ships = *self.ships_per_player.get(&owner_id).unwrap_or(&0);
+        if current_ships >= MAX_SHIPS_PER_PLAYER {
+            debug!("Player {} cannot launch ship: already has {}/{} ships", owner_id, current_ships, MAX_SHIPS_PER_PLAYER);
+            return None;
+        }
+
+        // Check path length
+        if path.is_empty() {
+            debug!("Cannot launch ship with empty path");
+            return None;
+        }
+
+        if path.len() > SHIP_MAX_PATH_LENGTH {
+            debug!("Cannot launch ship: path too long ({} > {})", path.len(), SHIP_MAX_PATH_LENGTH);
+            return None;
+        }
+
+        // Create the ship
+        let ship_id = self.next_ship_id;
+        self.next_ship_id += 1;
+
+        let ship = TransportShip::new(ship_id, owner_id, troops, path, SHIP_TICKS_PER_TILE, launch_tick);
+
+        self.ships.insert(ship_id, ship);
+        *self.ships_per_player.entry(owner_id).or_insert(0) += 1;
+
+        debug!("Launched ship {} for player {} with {} troops", ship_id, owner_id, troops);
+
+        Some(ship_id)
+    }
+
+    /// Update all ships and return list of ships that arrived at destination
+    /// Returns: Vec<(owner_id, target_tile, troops)>
+    pub fn update_ships(&mut self) -> Vec<(u16, usize, u32)> {
+        let mut arrivals = Vec::new();
+        let mut ships_to_remove = Vec::new();
+
+        for (ship_id, ship) in self.ships.iter_mut() {
+            if ship.update() {
+                // Ship has arrived at destination
+                arrivals.push((ship.owner_id, ship.target_tile, ship.troops));
+                ships_to_remove.push(*ship_id);
+            }
+        }
+
+        // Remove arrived ships
+        for ship_id in ships_to_remove {
+            if let Some(ship) = self.ships.remove(&ship_id) {
+                if let Some(count) = self.ships_per_player.get_mut(&ship.owner_id) {
+                    *count = count.saturating_sub(1);
+                    if *count == 0 {
+                        self.ships_per_player.remove(&ship.owner_id);
+                    }
+                }
+                debug!("Ship {} arrived at destination with {} troops", ship_id, ship.troops);
+            }
+        }
+
+        arrivals
+    }
+
+    /// Get all active ships
+    pub fn get_ships(&self) -> impl Iterator<Item = &TransportShip> {
+        self.ships.values()
+    }
+
+    /// Get ships for a specific player
+    pub fn get_player_ships(&self, player_id: u16) -> impl Iterator<Item = &TransportShip> {
+        self.ships.values().filter(move |ship| ship.owner_id == player_id)
+    }
+
+    /// Get number of ships for a player
+    pub fn get_ship_count(&self, player_id: u16) -> usize {
+        *self.ships_per_player.get(&player_id).unwrap_or(&0)
+    }
+
+    /// Remove all ships for a player (e.g., when player is eliminated)
+    pub fn remove_player_ships(&mut self, player_id: u16) {
+        let ships_to_remove: Vec<u32> = self.ships.iter().filter(|(_, ship)| ship.owner_id == player_id).map(|(id, _)| *id).collect();
+
+        for ship_id in ships_to_remove {
+            self.ships.remove(&ship_id);
+        }
+
+        self.ships_per_player.remove(&player_id);
+    }
+
+    /// Clear all ships
+    pub fn clear(&mut self) {
+        self.ships.clear();
+        self.ships_per_player.clear();
+        self.next_ship_id = 1;
+    }
+
+    /// Find the nearest coastal tile owned by a player to a target tile
+    /// Uses precomputed coastal tiles and player's border tiles for efficiency
+    /// Returns None if no valid coastal tile found
+    pub fn find_nearest_player_coastal_tile(coastal_tiles: &std::collections::HashSet<usize>, player_border_tiles: &std::collections::HashSet<usize>, target_tile: usize, width: usize) -> Option<usize> {
+        let target_x = target_tile % width;
+        let target_y = target_tile / width;
+
+        let mut best_tile = None;
+        let mut best_distance = usize::MAX;
+
+        // Filter player's border tiles for coastal ones
+        for &tile in player_border_tiles {
+            // Check if this tile is in the coastal set
+            if coastal_tiles.contains(&tile) {
+                let tile_x = tile % width;
+                let tile_y = tile / width;
+
+                // Calculate Manhattan distance to target
+                let dist = ((tile_x as i32 - target_x as i32).abs() + (tile_y as i32 - target_y as i32).abs()) as usize;
+
+                if dist < best_distance {
+                    best_distance = dist;
+                    best_tile = Some(tile);
+                }
+            }
+        }
+
+        best_tile
+    }
+}
+
+impl Default for ShipManager {
+    fn default() -> Self {
+        Self::new()
+    }
+}

crates/borders-core/src/game/ships/ship_pathfinding.rs

@@ -0,0 +1,310 @@
+use crate::game::terrain::TerrainData;
+use std::cmp::Ordering;
+use std::collections::{BinaryHeap, HashMap, HashSet};
+use tracing::debug;
+
+/// A node in the pathfinding search
+#[derive(Clone, Eq, PartialEq)]
+struct PathNode {
+    tile_idx: usize,
+    g_cost: u32, // Cost from start
+    h_cost: u32, // Heuristic cost to goal
+    f_cost: u32, // Total cost (g + h)
+    parent: Option<usize>,
+}
+
+impl Ord for PathNode {
+    fn cmp(&self, other: &Self) -> Ordering {
+        // Reverse ordering for min-heap
+        other.f_cost.cmp(&self.f_cost)
+    }
+}
+
+impl PartialOrd for PathNode {
+    fn partial_cmp(&self, other: &Self) -> Option<Ordering> {
+        Some(self.cmp(other))
+    }
+}
+
+/// Find a water path from start_tile to target_tile using A* algorithm
+/// Returns None if no path exists
+pub fn find_water_path(terrain: &TerrainData, start_tile: usize, target_tile: usize, max_path_length: usize) -> Option<Vec<usize>> {
+    let width = terrain.size().x as usize;
+    let height = terrain.size().y as usize;
+
+    // Check if target is reachable (must be coastal or water)
+    if !is_valid_ship_destination(terrain, target_tile, width, height) {
+        debug!("Pathfinding failed: target {} is not a valid ship destination", target_tile);
+        return None;
+    }
+
+    // Find actual water start position (adjacent to coast)
+    debug!("Pathfinding: looking for water launch tile adjacent to coastal tile {}", start_tile);
+    let water_start = find_water_launch_tile(terrain, start_tile, width, height)?;
+    debug!("Pathfinding: found water launch tile {}", water_start);
+
+    // Find water tiles adjacent to target if target is land
+    let target_x = target_tile % width;
+    let target_y = target_tile / width;
+    let water_targets = if terrain.is_navigable((target_x as u32, target_y as u32)) { vec![target_tile] } else { find_adjacent_water_tiles(terrain, target_tile, width, height) };
+
+    if water_targets.is_empty() {
+        return None;
+    }
+
+    // Run A* pathfinding
+    let mut open_set = BinaryHeap::new();
+    let mut closed_set = HashSet::new();
+    let mut came_from: HashMap<usize, usize> = HashMap::new();
+    let mut g_scores: HashMap<usize, u32> = HashMap::new();
+
+    // Initialize with start node
+    let start_h = heuristic_distance(water_start, water_targets[0], width);
+    open_set.push(PathNode { tile_idx: water_start, g_cost: 0, h_cost: start_h, f_cost: start_h, parent: None });
+    g_scores.insert(water_start, 0);
+
+    while let Some(current_node) = open_set.pop() {
+        let current = current_node.tile_idx;
+
+        // Check if we've reached any of the target tiles
+        if water_targets.contains(&current) {
+            // Reconstruct path
+            let mut path = vec![current];
+            let mut current_tile = current;
+
+            while let Some(&parent) = came_from.get(&current_tile) {
+                path.push(parent);
+                current_tile = parent;
+
+                // Prevent infinite loops
+                if path.len() > max_path_length {
+                    return None;
+                }
+            }
+
+            path.reverse();
+
+            // If original target was land, add it to the end
+            if !terrain.is_navigable((target_x as u32, target_y as u32)) {
+                path.push(target_tile);
+            }
+
+            return Some(path);
+        }
+
+        // Skip if already processed
+        if closed_set.contains(&current) {
+            continue;
+        }
+        closed_set.insert(current);
+
+        // Check if we've exceeded max path length
+        if current_node.g_cost as usize > max_path_length {
+            continue;
+        }
+
+        // Explore neighbors
+        let neighbors = get_water_neighbors(terrain, current, width, height);
+        for neighbor in neighbors {
+            if closed_set.contains(&neighbor) {
+                continue;
+            }
+
+            let tentative_g = current_node.g_cost + 1;
+
+            if tentative_g < *g_scores.get(&neighbor).unwrap_or(&u32::MAX) {
+                came_from.insert(neighbor, current);
+                g_scores.insert(neighbor, tentative_g);
+
+                // Find best heuristic to any target
+                let h_cost = water_targets.iter().map(|&t| heuristic_distance(neighbor, t, width)).min().unwrap_or(0);
+
+                let f_cost = tentative_g + h_cost;
+
+                open_set.push(PathNode { tile_idx: neighbor, g_cost: tentative_g, h_cost, f_cost, parent: Some(current) });
+            }
+        }
+    }
+
+    debug!("Pathfinding failed: no path found from {} to {}", start_tile, target_tile);
+    None // No path found
+}
+
+/// Calculate heuristic distance between two tiles (Manhattan distance)
+fn heuristic_distance(from: usize, to: usize, width: usize) -> u32 {
+    let from_x = from % width;
+    let from_y = from / width;
+    let to_x = to % width;
+    let to_y = to / width;
+
+    ((from_x as i32 - to_x as i32).abs() + (from_y as i32 - to_y as i32).abs()) as u32
+}
+
+/// Get water neighbors of a tile (4-directional movement)
+fn get_water_neighbors(terrain: &TerrainData, tile: usize, width: usize, height: usize) -> Vec<usize> {
+    let x = tile % width;
+    let y = tile / width;
+    let mut neighbors = Vec::with_capacity(4);
+
+    // Check 4 directions
+    let directions = [(0, -1), (1, 0), (0, 1), (-1, 0)];
+
+    for (dx, dy) in directions {
+        let nx = x as i32 + dx;
+        let ny = y as i32 + dy;
+
+        if nx >= 0 && ny >= 0 && (nx as usize) < width && (ny as usize) < height {
+            let neighbor_idx = nx as usize + ny as usize * width;
+            if terrain.is_navigable((nx as u32, ny as u32)) {
+                neighbors.push(neighbor_idx);
+            }
+        }
+    }
+
+    neighbors
+}
+
+/// Find a water tile adjacent to a coastal land tile for ship launch
+fn find_water_launch_tile(terrain: &TerrainData, coast_tile: usize, width: usize, height: usize) -> Option<usize> {
+    let x = coast_tile % width;
+    let y = coast_tile / width;
+
+    debug!("find_water_launch_tile: checking coastal tile {} at ({},{})", coast_tile, x, y);
+
+    // Check 4 directions for water
+    let directions = [(0, -1), (1, 0), (0, 1), (-1, 0)];
+
+    for (dx, dy) in directions {
+        let nx = x as i32 + dx;
+        let ny = y as i32 + dy;
+
+        if nx >= 0 && ny >= 0 && (nx as usize) < width && (ny as usize) < height {
+            let neighbor_idx = nx as usize + ny as usize * width;
+            let is_water = terrain.is_navigable((nx as u32, ny as u32));
+            debug!("  Checking neighbor ({},{}) -> tile {}: is_water={}", nx, ny, neighbor_idx, is_water);
+            if is_water {
+                debug!("  Found water launch tile {} at ({},{})", neighbor_idx, nx, ny);
+                return Some(neighbor_idx);
+            }
+        }
+    }
+
+    debug!("  No water launch tile found for coastal tile {}", coast_tile);
+    None
+}
+
+/// Find all water tiles adjacent to a land tile
+fn find_adjacent_water_tiles(terrain: &TerrainData, tile: usize, width: usize, height: usize) -> Vec<usize> {
+    let x = tile % width;
+    let y = tile / width;
+    let mut water_tiles = Vec::new();
+
+    // Check 4 directions for water
+    let directions = [(0, -1), (1, 0), (0, 1), (-1, 0)];
+
+    for (dx, dy) in directions {
+        let nx = x as i32 + dx;
+        let ny = y as i32 + dy;
+
+        if nx >= 0 && ny >= 0 && (nx as usize) < width && (ny as usize) < height {
+            let neighbor_idx = nx as usize + ny as usize * width;
+            if terrain.is_navigable((nx as u32, ny as u32)) {
+                water_tiles.push(neighbor_idx);
+            }
+        }
+    }
+
+    water_tiles
+}
+
+/// Check if a tile is a valid ship destination (water or coastal land)
+fn is_valid_ship_destination(terrain: &TerrainData, tile: usize, width: usize, height: usize) -> bool {
+    let x = tile % width;
+    let y = tile / width;
+
+    // If it's water, it's valid
+    if terrain.is_navigable((x as u32, y as u32)) {
+        return true;
+    }
+
+    // If it's land, check if it's coastal
+    let directions = [(0, -1), (1, 0), (0, 1), (-1, 0)];
+
+    for (dx, dy) in directions {
+        let nx = x as i32 + dx;
+        let ny = y as i32 + dy;
+
+        if nx >= 0 && ny >= 0 && (nx as usize) < width && (ny as usize) < height && terrain.is_navigable((nx as u32, ny as u32)) {
+            return true; // It's coastal
+        }
+    }
+
+    false
+}
+
+/// Simplify a path by removing unnecessary waypoints (path smoothing)
+/// This maintains determinism as it's purely geometric
+pub fn smooth_path(path: Vec<usize>, terrain: &TerrainData, width: usize) -> Vec<usize> {
+    if path.len() <= 2 {
+        return path;
+    }
+
+    let mut smoothed = vec![path[0]];
+    let mut current = 0;
+
+    while current < path.len() - 1 {
+        let mut farthest = current + 1;
+
+        // Find the farthest point we can see directly
+        for i in (current + 2)..path.len() {
+            if has_clear_water_line(terrain, path[current], path[i], width) {
+                farthest = i;
+            } else {
+                break;
+            }
+        }
+
+        smoothed.push(path[farthest]);
+        current = farthest;
+    }
+
+    smoothed
+}
+
+/// Check if there's a clear water line between two tiles
+/// Uses Bresenham-like algorithm for deterministic line checking
+fn has_clear_water_line(terrain: &TerrainData, from: usize, to: usize, width: usize) -> bool {
+    let x0 = (from % width) as i32;
+    let y0 = (from / width) as i32;
+    let x1 = (to % width) as i32;
+    let y1 = (to / width) as i32;
+
+    let dx = (x1 - x0).abs();
+    let dy = (y1 - y0).abs();
+    let sx = if x0 < x1 { 1 } else { -1 };
+    let sy = if y0 < y1 { 1 } else { -1 };
+    let mut err = dx - dy;
+
+    let mut x = x0;
+    let mut y = y0;
+
+    loop {
+        if !terrain.is_navigable((x as u32, y as u32)) {
+            return false; // Hit land
+        }
+
+        if x == x1 && y == y1 {
+            return true; // Reached target
+        }
+
+        let e2 = 2 * err;
+        if e2 > -dy {
+            err -= dy;
+            x += sx;
+        }
+        if e2 < dx {
+            err += dx;
+            y += sy;
+        }
+    }
+}

crates/borders-core/src/game/ships/transport_ship.rs

@@ -0,0 +1,88 @@
+use serde::{Deserialize, Serialize};
+
+/// A transport ship carrying troops across water
+/// Uses fixed-point arithmetic for deterministic calculations
+#[derive(Debug, Clone, Serialize, Deserialize)]
+pub struct TransportShip {
+    /// Unique identifier for this ship
+    pub id: u32,
+
+    /// Player who owns this ship
+    pub owner_id: u16,
+
+    /// Number of troops being transported (stored as integer)
+    pub troops: u32,
+
+    /// Pre-calculated path of tile indices
+    pub path: Vec<usize>,
+
+    /// Index of the current tile in the path
+    pub current_path_index: usize,
+
+    /// Movement speed in ticks per tile (e.g., 2 = move one tile every 2 ticks)
+    pub ticks_per_tile: u32,
+
+    /// Ticks since last tile transition
+    pub ticks_since_move: u32,
+
+    /// The tick when the ship was launched
+    pub launch_tick: u64,
+
+    /// The target tile (final destination)
+    pub target_tile: usize,
+}
+
+impl TransportShip {
+    /// Create a new transport ship
+    pub fn new(id: u32, owner_id: u16, troops: u32, path: Vec<usize>, ticks_per_tile: u32, launch_tick: u64) -> Self {
+        let target_tile = *path.last().unwrap_or(&path[0]);
+
+        Self { id, owner_id, troops, path, current_path_index: 0, ticks_per_tile, ticks_since_move: 0, launch_tick, target_tile }
+    }
+
+    /// Update the ship's position based on the current tick
+    /// Returns true if the ship has reached its destination
+    pub fn update(&mut self) -> bool {
+        if self.has_arrived() {
+            return true;
+        }
+
+        self.ticks_since_move += 1;
+
+        // Check if it's time to move to the next tile
+        if self.ticks_since_move >= self.ticks_per_tile {
+            self.ticks_since_move = 0;
+            self.current_path_index += 1;
+
+            if self.has_arrived() {
+                return true;
+            }
+        }
+
+        false
+    }
+
+    /// Get the current tile the ship is on
+    pub fn get_current_tile(&self) -> usize {
+        if self.current_path_index < self.path.len() { self.path[self.current_path_index] } else { self.target_tile }
+    }
+
+    /// Check if the ship has reached its destination
+    pub fn has_arrived(&self) -> bool {
+        self.current_path_index >= self.path.len() - 1
+    }
+
+    /// Get interpolation factor for smooth rendering (0.0 to 1.0)
+    /// This is only for visual interpolation and doesn't affect game logic
+    pub fn get_visual_interpolation(&self) -> f32 {
+        if self.ticks_per_tile == 0 {
+            return 1.0;
+        }
+        self.ticks_since_move as f32 / self.ticks_per_tile as f32
+    }
+
+    /// Get the next tile in the path (for interpolation)
+    pub fn get_next_tile(&self) -> Option<usize> {
+        if self.current_path_index + 1 < self.path.len() { Some(self.path[self.current_path_index + 1]) } else { None }
+    }
+}

crates/borders-core/src/game/spawn_manager.rs

@@ -0,0 +1,67 @@
+use bevy_ecs::prelude::*;
+
+/// Manages spawn positions during the pre-game spawn phase
+///
+/// This resource tracks bot and player spawn positions before the game starts ticking.
+/// It allows for dynamic recalculation of bot positions when players change their spawn
+/// location, implementing the two-pass spawn system described in the README.
+#[derive(Resource)]
+pub struct SpawnManager {
+    /// Initial bot spawn positions from first pass (player_id, tile_index)
+    pub initial_bot_spawns: Vec<(usize, usize)>,
+
+    /// Current bot spawn positions after recalculation (player_id, tile_index)
+    /// These are updated whenever a player chooses/changes their spawn
+    pub current_bot_spawns: Vec<(usize, usize)>,
+
+    /// Player spawn positions (player_id, tile_index)
+    /// Tracks human player spawn selections
+    pub player_spawns: Vec<(usize, usize)>,
+
+    /// RNG seed for deterministic spawn calculations
+    pub rng_seed: u64,
+
+    /// Map dimensions for distance calculations
+    pub map_width: u32,
+    pub map_height: u32,
+}
+
+impl SpawnManager {
+    /// Create a new SpawnManager with initial bot spawns
+    pub fn new(initial_bot_spawns: Vec<(usize, usize)>, rng_seed: u64, map_width: u32, map_height: u32) -> Self {
+        Self { current_bot_spawns: initial_bot_spawns.clone(), initial_bot_spawns, player_spawns: Vec::new(), rng_seed, map_width, map_height }
+    }
+
+    /// Update a player's spawn position and recalculate bot spawns if necessary
+    ///
+    /// This triggers the second pass of the two-pass spawn system, relocating
+    /// any bots that are too close to the new player position.
+    pub fn update_player_spawn(&mut self, player_id: usize, tile_index: usize, bot_manager: &crate::game::BotManager, territory_manager: &crate::game::TerritoryManager) {
+        // Update or add player spawn
+        if let Some(entry) = self.player_spawns.iter_mut().find(|(pid, _)| *pid == player_id) {
+            entry.1 = tile_index;
+        } else {
+            self.player_spawns.push((player_id, tile_index));
+        }
+
+        // Recalculate bot spawns with updated player positions
+        self.current_bot_spawns = bot_manager.recalculate_spawns_with_players(self.initial_bot_spawns.clone(), &self.player_spawns, territory_manager, self.rng_seed);
+    }
+
+    /// Get all current spawn positions (players + bots)
+    pub fn get_all_spawns(&self) -> Vec<(usize, usize)> {
+        let mut all_spawns = self.player_spawns.clone();
+        all_spawns.extend(self.current_bot_spawns.iter().copied());
+        all_spawns
+    }
+
+    /// Get only bot spawn positions
+    pub fn get_bot_spawns(&self) -> &[(usize, usize)] {
+        &self.current_bot_spawns
+    }
+
+    /// Get only player spawn positions
+    pub fn get_player_spawns(&self) -> &[(usize, usize)] {
+        &self.player_spawns
+    }
+}

crates/borders-core/src/game/spawn_timeout.rs

@@ -0,0 +1,74 @@
+use bevy_ecs::prelude::*;
+
+/// Tracks spawn phase timeout state on the client side
+///
+/// This resource is used to:
+/// - Show countdown timer in UI
+/// - Know when spawn phase is active
+/// - Calculate remaining time for display
+#[derive(Resource)]
+pub struct SpawnTimeout {
+    /// Whether spawn phase is currently active
+    pub active: bool,
+
+    /// Accumulated time since start (seconds)
+    pub elapsed_secs: f32,
+
+    /// Total timeout duration in seconds
+    pub duration_secs: f32,
+
+    /// Remaining time in seconds (updated each frame)
+    pub remaining_secs: f32,
+}
+
+impl Default for SpawnTimeout {
+    fn default() -> Self {
+        Self {
+            active: false,
+            elapsed_secs: 0.0,
+            duration_secs: 5.0, // Local mode: 5 seconds
+            remaining_secs: 5.0,
+        }
+    }
+}
+
+impl SpawnTimeout {
+    /// Create a new spawn timeout with specified duration
+    pub fn new(duration_secs: f32) -> Self {
+        Self { active: false, elapsed_secs: 0.0, duration_secs, remaining_secs: duration_secs }
+    }
+
+    /// Start the timeout countdown
+    pub fn start(&mut self) {
+        if self.elapsed_secs == 0.0 {
+            self.active = true;
+            self.elapsed_secs = 0.0;
+            self.remaining_secs = self.duration_secs;
+        }
+    }
+
+    /// Update remaining time (call each frame with delta time)
+    pub fn update(&mut self, delta_secs: f32) {
+        if !self.active {
+            return;
+        }
+
+        self.elapsed_secs += delta_secs;
+        self.remaining_secs = (self.duration_secs - self.elapsed_secs).max(0.0);
+
+        if self.remaining_secs <= 0.0 {
+            self.active = false;
+        }
+    }
+
+    /// Stop the timeout
+    pub fn stop(&mut self) {
+        self.active = false;
+        self.elapsed_secs = 0.0;
+    }
+
+    /// Check if timeout has expired
+    pub fn has_expired(&self) -> bool {
+        !self.active && self.remaining_secs <= 0.0
+    }
+}

crates/borders-core/src/game/terrain.rs

@@ -0,0 +1,270 @@
+use bevy_ecs::prelude::Resource;
+use glam::UVec2;
+use image::GenericImageView;
+use serde::{Deserialize, Serialize};
+use std::fs;
+use tracing::{debug, info};
+
+use crate::game::territory::get_idx;
+use crate::game::tilemap::TileMap;
+
+/// Calculate terrain color using pastel theme formulas
+fn calculate_theme_color(color_base: &str, color_variant: u8) -> [u8; 3] {
+    let i = color_variant as i32;
+
+    match color_base {
+        "grass" => {
+            // rgb(238 - 2 * i, 238 - 2 * i, 190 - i)
+            [(238 - 2 * i).clamp(0, 255) as u8, (238 - 2 * i).clamp(0, 255) as u8, (190 - i).clamp(0, 255) as u8]
+        }
+        "mountain" => {
+            // rgb(250 - 2 * i, 250 - 2 * i, 220 - i)
+            [(250 - 2 * i).clamp(0, 255) as u8, (250 - 2 * i).clamp(0, 255) as u8, (220 - i).clamp(0, 255) as u8]
+        }
+        "water" => {
+            // rgb(172 - 2 * i, 225 - 2 * i, 249 - 3 * i)
+            [(172 - 2 * i).clamp(0, 255) as u8, (225 - 2 * i).clamp(0, 255) as u8, (249 - 3 * i).clamp(0, 255) as u8]
+        }
+        _ => {
+            // Default fallback color (gray)
+            [128, 128, 128]
+        }
+    }
+}
+
+/// Helper structs for loading World.json format
+#[derive(Deserialize)]
+struct WorldMapJson {
+    tiles: Vec<WorldTileDef>,
+}
+
+#[derive(Deserialize)]
+struct WorldTileDef {
+    color: String,
+    name: String,
+    #[serde(default, rename = "colorBase")]
+    color_base: Option<String>,
+    #[serde(default, rename = "colorVariant")]
+    color_variant: Option<u32>,
+    conquerable: bool,
+    navigable: bool,
+    #[serde(default, rename = "expansionCost")]
+    expansion_cost: Option<u32>,
+    #[serde(default, rename = "expansionTime")]
+    expansion_time: Option<u32>,
+}
+
+/// Parse hex color string (#RRGGBB) to RGB bytes
+fn parse_hex_rgb(s: &str) -> Option<[u8; 3]> {
+    let s = s.trim_start_matches('#');
+    if s.len() != 6 {
+        return None;
+    }
+    let r = u8::from_str_radix(&s[0..2], 16).ok()?;
+    let g = u8::from_str_radix(&s[2..4], 16).ok()?;
+    let b = u8::from_str_radix(&s[4..6], 16).ok()?;
+    Some([r, g, b])
+}
+
+#[derive(Debug, Clone, Serialize, Deserialize)]
+pub struct TileType {
+    pub name: String,
+    pub color_base: String,
+    pub color_variant: u8,
+    pub conquerable: bool,
+    pub navigable: bool,
+    pub expansion_time: u8,
+    pub expansion_cost: u8,
+}
+
+/// Map manifest structure
+#[derive(Debug, Clone, Deserialize, Serialize)]
+pub struct MapManifest {
+    pub map: MapMetadata,
+    pub name: String,
+    pub nations: Vec<NationSpawn>,
+}
+
+/// Map size metadata
+#[derive(Debug, Clone, Deserialize, Serialize)]
+pub struct MapMetadata {
+    pub width: usize,
+    pub height: usize,
+    pub num_land_tiles: usize,
+}
+
+/// Nation spawn point
+#[derive(Debug, Clone, Deserialize, Serialize)]
+pub struct NationSpawn {
+    pub coordinates: [usize; 2],
+    pub flag: String,
+    pub name: String,
+    pub strength: u32,
+}
+
+/// Loaded map data
+#[derive(Debug, Clone, Resource)]
+pub struct TerrainData {
+    pub _manifest: MapManifest,
+    /// Legacy terrain data (for backward compatibility)
+    pub terrain_data: TileMap<u8>,
+    /// Tile type indices (new format)
+    pub tiles: Vec<u8>,
+    /// Tile type definitions
+    pub tile_types: Vec<TileType>,
+}
+
+impl TerrainData {
+    /// Load the World map from embedded assets
+    pub fn load_world_map() -> Result<Self, Box<dyn std::error::Error>> {
+        const MAP_JSON: &[u8] = include_bytes!("../../assets/maps/World.json");
+        const MAP_PNG: &[u8] = include_bytes!("../../assets/maps/World.png");
+
+        // Parse JSON tile definitions
+        let map_json: WorldMapJson = serde_json::from_slice(MAP_JSON)?;
+
+        // Load PNG image
+        let png = image::load_from_memory(MAP_PNG)?;
+        let (width, height) = png.dimensions();
+
+        info!("Loading World map: {}x{}", width, height);
+
+        // Build color-to-index lookup table
+        let color_to_index: Vec<([u8; 3], usize)> = map_json.tiles.iter().enumerate().filter_map(|(idx, t)| parse_hex_rgb(&t.color).map(|rgb| (rgb, idx))).collect();
+
+        let mut tiles = vec![0u8; (width * height) as usize];
+        let mut terrain_data_raw = vec![0u8; (width * height) as usize];
+
+        // Match each pixel to nearest tile type by color
+        for y in 0..height {
+            for x in 0..width {
+                let pixel = png.get_pixel(x, y).0;
+                let rgb = [pixel[0], pixel[1], pixel[2]];
+
+                // Find nearest tile by RGB distance
+                let (tile_idx, _) = color_to_index
+                    .iter()
+                    .map(|(c, idx)| {
+                        let dr = rgb[0] as i32 - c[0] as i32;
+                        let dg = rgb[1] as i32 - c[1] as i32;
+                        let db = rgb[2] as i32 - c[2] as i32;
+                        let dist = (dr * dr + dg * dg + db * db) as u32;
+                        (idx, dist)
+                    })
+                    .min_by_key(|(_, d)| *d)
+                    .unwrap();
+
+                let i = (y * width + x) as usize;
+                tiles[i] = *tile_idx as u8;
+
+                // Set bit 7 if conquerable (land)
+                if map_json.tiles[*tile_idx].conquerable {
+                    terrain_data_raw[i] |= 0x80;
+                }
+                // Lower 5 bits for terrain magnitude (unused for World map)
+            }
+        }
+
+        // Convert to TileType format
+        let tile_types = map_json.tiles.into_iter().map(|t| TileType { name: t.name, color_base: t.color_base.unwrap_or_default(), color_variant: t.color_variant.unwrap_or(0) as u8, conquerable: t.conquerable, navigable: t.navigable, expansion_cost: t.expansion_cost.unwrap_or(50) as u8, expansion_time: t.expansion_time.unwrap_or(50) as u8 }).collect();
+
+        let num_land_tiles = terrain_data_raw.iter().filter(|&&b| b & 0x80 != 0).count();
+
+        info!("World map loaded: {} land tiles", num_land_tiles);
+
+        Ok(Self { _manifest: MapManifest { name: "World".to_string(), map: MapMetadata { width: width as usize, height: height as usize, num_land_tiles }, nations: vec![] }, terrain_data: TileMap::from_vec(width, height, terrain_data_raw), tiles, tile_types })
+    }
+
+    /// Load a map from the resources directory
+    pub fn load(map_name: &str) -> Result<Self, Box<dyn std::error::Error>> {
+        let base_path = format!("resources/maps/{}", map_name);
+
+        // Load manifest
+        let manifest_path = format!("{}/manifest.json", base_path);
+        let manifest_json = fs::read_to_string(&manifest_path)?;
+        let manifest: MapManifest = serde_json::from_str(&manifest_json)?;
+
+        // Load binary map data
+        let map_path = format!("{}/map.bin", base_path);
+        let terrain_data_raw = fs::read(&map_path)?;
+
+        let width = manifest.map.width as u32;
+        let height = manifest.map.height as u32;
+
+        // Verify data size
+        if terrain_data_raw.len() != (width * height) as usize {
+            return Err(format!("Map data size mismatch: expected {} bytes, got {}", width * height, terrain_data_raw.len()).into());
+        }
+
+        info!("Loaded map '{}' ({}x{})", manifest.name, width, height);
+        debug!("Land tiles: {}/{}", manifest.map.num_land_tiles, width * height);
+
+        // Create default tile types for legacy format
+        let tile_types = vec![TileType { name: "water".to_string(), color_base: "water".to_string(), color_variant: 0, conquerable: false, navigable: true, expansion_time: 255, expansion_cost: 255 }, TileType { name: "land".to_string(), color_base: "grass".to_string(), color_variant: 0, conquerable: true, navigable: false, expansion_time: 50, expansion_cost: 50 }];
+
+        // Convert legacy format to tile indices
+        let tiles: Vec<u8> = terrain_data_raw.iter().map(|&byte| if byte & 0x80 != 0 { 1 } else { 0 }).collect();
+
+        // Create TileMap from terrain data
+        let terrain_data = TileMap::from_vec(width, height, terrain_data_raw);
+
+        Ok(Self { _manifest: manifest, terrain_data, tiles, tile_types })
+    }
+
+    /// Get the size of the map
+    pub fn size(&self) -> UVec2 {
+        UVec2::new(self.terrain_data.width(), self.terrain_data.height())
+    }
+
+    pub fn get_value<T: Into<UVec2>>(&self, pos: T) -> u8 {
+        self.terrain_data[get_idx(pos, self.terrain_data.width())]
+    }
+
+    /// Check if a tile is land (bit 7 set)
+    pub fn is_land<T: Into<UVec2>>(&self, pos: T) -> bool {
+        self.get_value(pos) & 0x80 != 0
+    }
+
+    /// Get terrain magnitude (bits 0-4)
+    pub fn terrain_magnitude<T: Into<UVec2>>(&self, pos: T) -> u8 {
+        self.get_value(pos) & 0b00011111
+    }
+
+    /// Get tile type at position
+    pub fn get_tile_type<T: Into<UVec2>>(&self, pos: T) -> &TileType {
+        let idx = get_idx(pos, self.terrain_data.width());
+        &self.tile_types[self.tiles[idx] as usize]
+    }
+
+    /// Check if a tile is conquerable
+    pub fn is_conquerable<T: Into<UVec2>>(&self, pos: T) -> bool {
+        self.get_tile_type(pos).conquerable
+    }
+
+    /// Check if a tile is navigable (water)
+    pub fn is_navigable<T: Into<UVec2>>(&self, pos: T) -> bool {
+        self.get_tile_type(pos).navigable
+    }
+
+    /// Get expansion time for a tile
+    pub fn get_expansion_time<T: Into<UVec2>>(&self, pos: T) -> u8 {
+        self.get_tile_type(pos).expansion_time
+    }
+
+    /// Get expansion cost for a tile
+    pub fn get_expansion_cost<T: Into<UVec2>>(&self, pos: T) -> u8 {
+        self.get_tile_type(pos).expansion_cost
+    }
+
+    /// Get tile type IDs for rendering (each position maps to a tile type)
+    pub fn get_tile_ids(&self) -> &[u8] {
+        &self.tiles
+    }
+
+    /// Get terrain palette colors from tile types (for rendering)
+    /// Returns a vec where index = tile type ID, value = RGB color
+    /// Colors are calculated using theme formulas based on colorBase and colorVariant
+    pub fn get_terrain_palette_colors(&self) -> Vec<[u8; 3]> {
+        self.tile_types.iter().map(|tile_type| calculate_theme_color(&tile_type.color_base, tile_type.color_variant)).collect()
+    }
+}

crates/borders-core/src/game/territory.rs

@@ -0,0 +1,21 @@
+use glam::{IVec2, UVec2};
+
+/// Convert 2D coordinates to a flat array index
+pub fn get_idx<T: Into<UVec2>>(pos: T, width: u32) -> usize {
+    let pos = pos.into();
+    pos.x as usize + pos.y as usize * width as usize
+}
+
+const CARDINAL_DIRECTIONS: [IVec2; 4] = [IVec2::new(0, 1), IVec2::new(1, 0), IVec2::new(0, -1), IVec2::new(-1, 0)];
+
+/// Returns an iterator over the valid cardinal neighbors of a tile.
+///
+/// Requires the width and height of the map to be passed in to ensure the neighbor is within bounds.
+pub fn get_neighbors(pos: UVec2, width: u32, height: u32) -> impl Iterator<Item = UVec2> {
+    let in_bounds = move |neighbor: IVec2| (0..width).contains(&(neighbor.x as u32)) && (0..height).contains(&(neighbor.y as u32));
+
+    CARDINAL_DIRECTIONS.into_iter().filter_map(move |dir| {
+        let neighbor = pos.as_ivec2().saturating_add(dir);
+        in_bounds(neighbor).then_some(neighbor.as_uvec2())
+    })
+}

crates/borders-core/src/game/territory_manager.rs

@@ -0,0 +1,202 @@
+use crate::game::tile_ownership::{ENCODED_WATER, TileOwnership};
+use crate::game::tilemap::TileMap;
+use crate::game::tilemap_changes::ChangeBuffer;
+
+/// Deprecated: Use TileOwnership::Water instead
+/// Kept for backward compatibility during migration
+pub const OWNER_WATER: u16 = ENCODED_WATER;
+
+/// Manages territory ownership for all tiles
+pub struct TerritoryManager {
+    tile_owners: TileMap<TileOwnership>,
+    changes: ChangeBuffer,
+    /// Cached u16 representation for efficient serialization to frontend
+    u16_cache: Vec<u16>,
+    cache_dirty: bool,
+}
+
+impl TerritoryManager {
+    /// Creates a new territory manager
+    pub fn new(width: u32, height: u32) -> Self {
+        let size = (width * height) as usize;
+        Self { tile_owners: TileMap::with_default(width, height, TileOwnership::Unclaimed), changes: ChangeBuffer::with_capacity((width * height / 100) as usize), u16_cache: vec![0; size], cache_dirty: true }
+    }
+
+    /// Resets the territory manager
+    /// Should only be called when a new game is started
+    pub fn reset(&mut self, width: u32, height: u32, conquerable_tiles: &[bool]) {
+        self.tile_owners = TileMap::with_default(width, height, TileOwnership::Unclaimed);
+        self.changes.clear();
+
+        for (i, &conquerable) in conquerable_tiles.iter().enumerate() {
+            if !conquerable {
+                self.tile_owners[i] = TileOwnership::Water;
+            }
+        }
+
+        let size = (width * height) as usize;
+        self.u16_cache.resize(size, 0);
+        self.cache_dirty = true;
+    }
+
+    /// Checks if a tile is a border tile of the territory of its owner
+    /// A tile is a border tile if it is adjacent to a tile that is not owned by the same player
+    pub fn is_border(&self, tile: usize) -> bool {
+        let pos = self.tile_owners.index_to_pos(tile);
+        let owner = self.tile_owners[tile];
+
+        // Border if on map edge
+        if pos.x == 0 || pos.x == self.tile_owners.width() - 1 || pos.y == 0 || pos.y == self.tile_owners.height() - 1 {
+            return true;
+        }
+
+        // Border if any neighbor has different owner
+        for neighbor_pos in self.tile_owners.neighbors(pos) {
+            if self.tile_owners[neighbor_pos] != owner {
+                return true;
+            }
+        }
+
+        false
+    }
+
+    /// Checks if a tile has an owner
+    pub fn has_owner(&self, tile: usize) -> bool {
+        self.tile_owners[tile].is_owned()
+    }
+
+    /// Checks if a tile is owned by a specific player
+    pub fn is_owner(&self, tile: usize, owner: usize) -> bool {
+        self.tile_owners[tile].is_owned_by(owner as u16)
+    }
+
+    /// Gets the owner of a tile as u16 (for compatibility)
+    /// Returns the encoded u16 value (nation_id, or ENCODED_UNCLAIMED/ENCODED_WATER)
+    pub fn get_owner(&self, tile: usize) -> u16 {
+        self.tile_owners[tile].to_u16()
+    }
+
+    /// Gets the ownership enum for a tile
+    pub fn get_ownership(&self, tile: usize) -> TileOwnership {
+        self.tile_owners[tile]
+    }
+
+    /// Checks if a tile is water
+    pub fn is_water(&self, tile: usize) -> bool {
+        self.tile_owners[tile].is_water()
+    }
+
+    /// Conquers a tile for a player
+    /// If the tile is already owned by a player, that player will lose the tile
+    /// Only records a change if the owner actually changed
+    pub fn conquer(&mut self, tile: usize, owner: usize) -> u16 {
+        let previous_owner = self.tile_owners[tile];
+        let new_ownership = TileOwnership::Owned(owner as u16);
+
+        // Only update and track change if the owner actually changed
+        if previous_owner != new_ownership {
+            self.tile_owners[tile] = new_ownership;
+            self.changes.push(tile);
+            self.cache_dirty = true;
+        }
+
+        previous_owner.to_u16()
+    }
+
+    /// Clears a tile (removes ownership)
+    pub fn clear(&mut self, tile: usize) -> Option<u16> {
+        let ownership = self.tile_owners[tile];
+        if ownership.is_owned() {
+            self.tile_owners[tile] = TileOwnership::Unclaimed;
+            self.changes.push(tile);
+            self.cache_dirty = true;
+            ownership.nation_id()
+        } else {
+            None
+        }
+    }
+
+    /// Get width of the map
+    pub fn width(&self) -> u32 {
+        self.tile_owners.width()
+    }
+
+    /// Get height of the map
+    pub fn height(&self) -> u32 {
+        self.tile_owners.height()
+    }
+
+    /// Returns a reference to the underlying tile ownership data as a slice of enums
+    pub fn as_slice(&self) -> &[TileOwnership] {
+        self.tile_owners.as_slice()
+    }
+
+    /// Returns the tile ownership data as u16 values for frontend serialization
+    /// This is cached and only recomputed when ownership changes
+    pub fn as_u16_slice(&mut self) -> &[u16] {
+        if self.cache_dirty {
+            for (i, ownership) in self.tile_owners.as_slice().iter().enumerate() {
+                self.u16_cache[i] = ownership.to_u16();
+            }
+            self.cache_dirty = false;
+        }
+        &self.u16_cache
+    }
+
+    /// Converts tile ownership to a Vec<u16> for serialization (immutable)
+    /// Use this when you need a Vec for creating Arc<[u16]>
+    pub fn to_u16_vec(&self) -> Vec<u16> {
+        self.tile_owners.as_slice().iter().map(|ownership| ownership.to_u16()).collect()
+    }
+
+    /// Returns the number of tiles in the map
+    pub fn len(&self) -> usize {
+        self.tile_owners.len()
+    }
+
+    /// Returns true if the map has no tiles
+    pub fn is_empty(&self) -> bool {
+        self.tile_owners.len() == 0
+    }
+
+    /// Returns an iterator over changed tile indices without consuming them
+    /// Use this to read changes without clearing the buffer
+    pub fn iter_changes(&self) -> impl Iterator<Item = usize> + '_ {
+        self.changes.iter()
+    }
+
+    /// Drains all changed tile indices, returning an iterator and clearing the change buffer
+    pub fn drain_changes(&mut self) -> impl Iterator<Item = usize> + '_ {
+        self.changes.drain()
+    }
+
+    /// Returns true if any territory changes have been recorded since last drain
+    pub fn has_changes(&self) -> bool {
+        self.changes.has_changes()
+    }
+
+    /// Clears all tracked changes without returning them
+    pub fn clear_changes(&mut self) {
+        self.changes.clear()
+    }
+
+    /// Calls a closure for each neighbor using tile indices
+    pub fn on_neighbor_indices<F>(&self, index: usize, closure: F)
+    where
+        F: FnMut(usize),
+    {
+        self.tile_owners.on_neighbor_indices(index, closure)
+    }
+
+    /// Checks if any neighbor has a different owner than the specified owner
+    /// This is optimized for border detection with early exit
+    pub fn any_neighbor_has_different_owner(&self, tile: usize, owner: u16) -> bool {
+        let mut has_different = false;
+        self.on_neighbor_indices(tile, |neighbor| {
+            if !has_different && self.tile_owners[neighbor].to_u16() != owner {
+                has_different = true;
+            }
+        });
+        has_different
+    }
+}

crates/borders-core/src/game/tile_ownership.rs

@@ -0,0 +1,159 @@
+//! Tile ownership representation
+//!
+//! This module defines how tiles are owned and what their terrain type is.
+//! It separates the concept of "who owns this tile" from "what type of terrain is this".
+//!
+//! ## Encoding
+//!
+//! For frontend serialization, TileOwnership is encoded as a u16:
+//! - 0-65533: Nation IDs (supports 400+ nations)
+//! - 65534: Unclaimed land
+//! - 65535: Water (unconquerable terrain)
+
+use serde::{Deserialize, Serialize};
+
+/// Encoded value for unclaimed land in u16 representation
+pub const ENCODED_UNCLAIMED: u16 = 65534;
+
+/// Encoded value for water in u16 representation
+/// Kept at 65535 for backward compatibility with OWNER_WATER
+pub const ENCODED_WATER: u16 = 65535;
+
+/// Represents the ownership/state of a single tile
+///
+/// This enum clearly separates nation ownership from terrain type,
+/// allowing nation ID 0 to be valid without confusion with wilderness.
+#[derive(Debug, Copy, Clone, Eq, PartialEq, Serialize, Deserialize, Default)]
+pub enum TileOwnership {
+    /// Owned by a nation (0-65533, supporting 65,534 possible nations)
+    Owned(u16),
+    /// Unclaimed but conquerable land
+    #[default]
+    Unclaimed,
+    /// Water (unconquerable terrain)
+    Water,
+}
+
+impl TileOwnership {
+    /// Convert to u16 for frontend serialization
+    pub fn to_u16(self) -> u16 {
+        match self {
+            TileOwnership::Owned(nation_id) => nation_id,
+            TileOwnership::Unclaimed => ENCODED_UNCLAIMED,
+            TileOwnership::Water => ENCODED_WATER,
+        }
+    }
+
+    /// Convert from u16 (frontend serialization format)
+    pub fn from_u16(value: u16) -> Self {
+        match value {
+            ENCODED_WATER => TileOwnership::Water,
+            ENCODED_UNCLAIMED => TileOwnership::Unclaimed,
+            nation_id => TileOwnership::Owned(nation_id),
+        }
+    }
+
+    /// Check if this tile is owned by any nation
+    pub fn is_owned(self) -> bool {
+        matches!(self, TileOwnership::Owned(_))
+    }
+
+    /// Check if this tile is unclaimed land
+    pub fn is_unclaimed(self) -> bool {
+        matches!(self, TileOwnership::Unclaimed)
+    }
+
+    /// Check if this tile is water
+    pub fn is_water(self) -> bool {
+        matches!(self, TileOwnership::Water)
+    }
+
+    /// Get the nation ID if this tile is owned, otherwise None
+    pub fn nation_id(self) -> Option<u16> {
+        match self {
+            TileOwnership::Owned(id) => Some(id),
+            _ => None,
+        }
+    }
+
+    /// Check if this tile is owned by a specific nation
+    pub fn is_owned_by(self, nation_id: u16) -> bool {
+        matches!(self, TileOwnership::Owned(id) if id == nation_id)
+    }
+}
+
+impl From<u16> for TileOwnership {
+    fn from(value: u16) -> Self {
+        Self::from_u16(value)
+    }
+}
+
+impl From<TileOwnership> for u16 {
+    fn from(ownership: TileOwnership) -> Self {
+        ownership.to_u16()
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn test_encoding_nation_ids() {
+        for nation_id in [0, 1, 100, 1000, 65533] {
+            let ownership = TileOwnership::Owned(nation_id);
+            let encoded = ownership.to_u16();
+            assert_eq!(encoded, nation_id);
+            assert_eq!(TileOwnership::from_u16(encoded), ownership);
+        }
+    }
+
+    #[test]
+    fn test_encoding_unclaimed() {
+        let ownership = TileOwnership::Unclaimed;
+        let encoded = ownership.to_u16();
+        assert_eq!(encoded, ENCODED_UNCLAIMED);
+        assert_eq!(TileOwnership::from_u16(encoded), ownership);
+    }
+
+    #[test]
+    fn test_encoding_water() {
+        let ownership = TileOwnership::Water;
+        let encoded = ownership.to_u16();
+        assert_eq!(encoded, ENCODED_WATER);
+        assert_eq!(TileOwnership::from_u16(encoded), ownership);
+    }
+
+    #[test]
+    fn test_is_owned() {
+        assert!(TileOwnership::Owned(0).is_owned());
+        assert!(TileOwnership::Owned(100).is_owned());
+        assert!(!TileOwnership::Unclaimed.is_owned());
+        assert!(!TileOwnership::Water.is_owned());
+    }
+
+    #[test]
+    fn test_is_owned_by() {
+        assert!(TileOwnership::Owned(5).is_owned_by(5));
+        assert!(!TileOwnership::Owned(5).is_owned_by(6));
+        assert!(!TileOwnership::Unclaimed.is_owned_by(5));
+        assert!(!TileOwnership::Water.is_owned_by(5));
+    }
+
+    #[test]
+    fn test_nation_id() {
+        assert_eq!(TileOwnership::Owned(42).nation_id(), Some(42));
+        assert_eq!(TileOwnership::Unclaimed.nation_id(), None);
+        assert_eq!(TileOwnership::Water.nation_id(), None);
+    }
+
+    #[test]
+    fn test_nation_zero_is_valid() {
+        let ownership = TileOwnership::Owned(0);
+        assert!(ownership.is_owned());
+        assert!(ownership.is_owned_by(0));
+        assert_eq!(ownership.nation_id(), Some(0));
+        assert_ne!(ownership, TileOwnership::Unclaimed);
+        assert_ne!(ownership, TileOwnership::Water);
+    }
+}

crates/borders-core/src/game/tilemap.rs

@@ -0,0 +1,441 @@
+use glam::UVec2;
+use std::ops::{Index, IndexMut};
+
+/// A 2D grid-based map structure optimized for tile-based games.
+///
+/// Provides efficient access to tiles using 2D coordinates (UVec2) while maintaining
+/// cache-friendly contiguous memory layout. Supports generic tile types that implement Copy.
+///
+/// # Type Parameters
+/// * `T` - The tile value type. Must implement `Copy` for efficient access.
+///
+/// # Examples
+/// ```
+/// use glam::UVec2;
+/// use borders_core::game::TileMap;
+///
+/// let mut map = TileMap::<u8>::new(10, 10);
+/// map[UVec2::new(5, 5)] = 42;
+/// assert_eq!(map[UVec2::new(5, 5)], 42);
+/// ```
+#[derive(Clone, Debug)]
+pub struct TileMap<T: Copy> {
+    tiles: Box<[T]>,
+    width: u32,
+    height: u32,
+}
+
+impl<T: Copy> TileMap<T> {
+    /// Creates a new TileMap with the specified dimensions and default value.
+    ///
+    /// # Arguments
+    /// * `width` - The width of the map in tiles
+    /// * `height` - The height of the map in tiles
+    /// * `default` - The default value to initialize all tiles with
+    pub fn with_default(width: u32, height: u32, default: T) -> Self {
+        let capacity = (width * height) as usize;
+        let tiles = vec![default; capacity].into_boxed_slice();
+        Self { tiles, width, height }
+    }
+
+    /// Creates a TileMap from an existing vector of tile data.
+    ///
+    /// # Arguments
+    /// * `width` - The width of the map in tiles
+    /// * `height` - The height of the map in tiles
+    /// * `data` - Vector containing tile data in row-major order
+    ///
+    /// # Panics
+    /// Panics if `data.len() != width * height`
+    pub fn from_vec(width: u32, height: u32, data: Vec<T>) -> Self {
+        assert_eq!(data.len(), (width * height) as usize, "Data length must match width * height");
+        Self { tiles: data.into_boxed_slice(), width, height }
+    }
+
+    /// Converts the position to a flat array index.
+    ///
+    /// # Safety
+    /// Debug builds will assert that the position is in bounds.
+    /// Release builds skip the check for performance.
+    #[inline]
+    pub fn pos_to_index(&self, pos: UVec2) -> usize {
+        debug_assert!(pos.x < self.width && pos.y < self.height);
+        (pos.y * self.width + pos.x) as usize
+    }
+
+    /// Converts a flat array index to a 2D position.
+    #[inline]
+    pub fn index_to_pos(&self, index: usize) -> UVec2 {
+        debug_assert!(index < self.tiles.len());
+        UVec2::new((index as u32) % self.width, (index as u32) / self.width)
+    }
+
+    /// Checks if a position is within the map bounds.
+    #[inline]
+    pub fn in_bounds(&self, pos: UVec2) -> bool {
+        pos.x < self.width && pos.y < self.height
+    }
+
+    /// Gets the tile value at the specified position.
+    ///
+    /// Returns `None` if the position is out of bounds.
+    pub fn get(&self, pos: UVec2) -> Option<T> {
+        if self.in_bounds(pos) { Some(self.tiles[self.pos_to_index(pos)]) } else { None }
+    }
+
+    /// Sets the tile value at the specified position.
+    ///
+    /// Returns `true` if the position was in bounds and the value was set,
+    /// `false` otherwise.
+    pub fn set(&mut self, pos: UVec2, tile: T) -> bool {
+        if self.in_bounds(pos) {
+            let idx = self.pos_to_index(pos);
+            self.tiles[idx] = tile;
+            true
+        } else {
+            false
+        }
+    }
+
+    /// Returns the width of the map.
+    #[inline]
+    pub fn width(&self) -> u32 {
+        self.width
+    }
+
+    /// Returns the height of the map.
+    #[inline]
+    pub fn height(&self) -> u32 {
+        self.height
+    }
+
+    /// Returns the total number of tiles in the map.
+    #[inline]
+    pub fn len(&self) -> usize {
+        self.tiles.len()
+    }
+
+    /// Returns `true` if the map contains no tiles.
+    #[inline]
+    pub fn is_empty(&self) -> bool {
+        self.tiles.is_empty()
+    }
+
+    /// Returns an iterator over all valid cardinal neighbors of a position.
+    ///
+    /// Yields positions for up, down, left, and right neighbors that are within bounds.
+    pub fn neighbors(&self, pos: UVec2) -> impl Iterator<Item = UVec2> + '_ {
+        const CARDINAL_DIRECTIONS: [(i32, i32); 4] = [(0, 1), (1, 0), (0, -1), (-1, 0)];
+
+        let pos_i32 = (pos.x as i32, pos.y as i32);
+        let width = self.width;
+        let height = self.height;
+
+        CARDINAL_DIRECTIONS.iter().filter_map(move |(dx, dy)| {
+            let nx = pos_i32.0 + dx;
+            let ny = pos_i32.1 + dy;
+            if nx >= 0 && ny >= 0 && nx < width as i32 && ny < height as i32 { Some(UVec2::new(nx as u32, ny as u32)) } else { None }
+        })
+    }
+
+    /// Calls a closure for each valid cardinal neighbor of a position.
+    ///
+    /// This is more efficient than using the `neighbors()` iterator when you don't
+    /// need to collect the neighbors.
+    pub fn on_neighbors<F>(&self, pos: UVec2, mut closure: F)
+    where
+        F: FnMut(UVec2),
+    {
+        if pos.x > 0 {
+            closure(UVec2::new(pos.x - 1, pos.y));
+        }
+        if pos.x < self.width - 1 {
+            closure(UVec2::new(pos.x + 1, pos.y));
+        }
+        if pos.y > 0 {
+            closure(UVec2::new(pos.x, pos.y - 1));
+        }
+        if pos.y < self.height - 1 {
+            closure(UVec2::new(pos.x, pos.y + 1));
+        }
+    }
+
+    /// Calls a closure for each neighbor using tile indices instead of positions.
+    ///
+    /// This is useful when working with systems that still use raw indices.
+    pub fn on_neighbor_indices<F>(&self, index: usize, mut closure: F)
+    where
+        F: FnMut(usize),
+    {
+        let width = self.width as usize;
+        let height = self.height as usize;
+        let x = index % width;
+        let y = index / width;
+
+        if x > 0 {
+            closure(index - 1);
+        }
+        if x < width - 1 {
+            closure(index + 1);
+        }
+        if y > 0 {
+            closure(index - width);
+        }
+        if y < height - 1 {
+            closure(index + width);
+        }
+    }
+
+    /// Returns an iterator over all positions and their tile values.
+    pub fn iter(&self) -> impl Iterator<Item = (UVec2, T)> + '_ {
+        (0..self.height).flat_map(move |y| {
+            (0..self.width).map(move |x| {
+                let pos = UVec2::new(x, y);
+                (pos, self[pos])
+            })
+        })
+    }
+
+    /// Returns an iterator over just the tile values.
+    pub fn iter_values(&self) -> impl Iterator<Item = T> + '_ {
+        self.tiles.iter().copied()
+    }
+
+    /// Returns an iterator over all positions in the map.
+    pub fn positions(&self) -> impl Iterator<Item = UVec2> + '_ {
+        (0..self.height).flat_map(move |y| (0..self.width).map(move |x| UVec2::new(x, y)))
+    }
+
+    /// Returns an iterator over tile indices, positions, and values.
+    pub fn enumerate(&self) -> impl Iterator<Item = (usize, UVec2, T)> + '_ {
+        self.tiles.iter().enumerate().map(move |(idx, &value)| {
+            let pos = self.index_to_pos(idx);
+            (idx, pos, value)
+        })
+    }
+
+    /// Returns a reference to the underlying tile data as a slice.
+    pub fn as_slice(&self) -> &[T] {
+        &self.tiles
+    }
+
+    /// Returns a mutable reference to the underlying tile data as a slice.
+    pub fn as_mut_slice(&mut self) -> &mut [T] {
+        &mut self.tiles
+    }
+}
+
+impl<T: Copy + Default> TileMap<T> {
+    /// Creates a new TileMap with the specified dimensions, using T::default() for initialization.
+    pub fn new(width: u32, height: u32) -> Self {
+        Self::with_default(width, height, T::default())
+    }
+}
+
+impl<T: Copy> Index<UVec2> for TileMap<T> {
+    type Output = T;
+
+    #[inline]
+    fn index(&self, pos: UVec2) -> &Self::Output {
+        &self.tiles[self.pos_to_index(pos)]
+    }
+}
+
+impl<T: Copy> IndexMut<UVec2> for TileMap<T> {
+    #[inline]
+    fn index_mut(&mut self, pos: UVec2) -> &mut Self::Output {
+        let idx = self.pos_to_index(pos);
+        &mut self.tiles[idx]
+    }
+}
+
+impl<T: Copy> Index<usize> for TileMap<T> {
+    type Output = T;
+
+    #[inline]
+    fn index(&self, index: usize) -> &Self::Output {
+        &self.tiles[index]
+    }
+}
+
+impl<T: Copy> IndexMut<usize> for TileMap<T> {
+    #[inline]
+    fn index_mut(&mut self, index: usize) -> &mut Self::Output {
+        &mut self.tiles[index]
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn test_new_with_default() {
+        let map = TileMap::<u8>::with_default(10, 10, 42);
+        assert_eq!(map.width(), 10);
+        assert_eq!(map.height(), 10);
+        assert_eq!(map[UVec2::new(0, 0)], 42);
+        assert_eq!(map[UVec2::new(9, 9)], 42);
+    }
+
+    #[test]
+    fn test_from_vec() {
+        let data = vec![1u8, 2, 3, 4];
+        let map = TileMap::from_vec(2, 2, data);
+        assert_eq!(map[UVec2::new(0, 0)], 1);
+        assert_eq!(map[UVec2::new(1, 0)], 2);
+        assert_eq!(map[UVec2::new(0, 1)], 3);
+        assert_eq!(map[UVec2::new(1, 1)], 4);
+    }
+
+    #[test]
+    fn test_pos_to_index() {
+        let map = TileMap::<u8>::with_default(10, 10, 0);
+        assert_eq!(map.pos_to_index(UVec2::new(0, 0)), 0);
+        assert_eq!(map.pos_to_index(UVec2::new(5, 0)), 5);
+        assert_eq!(map.pos_to_index(UVec2::new(0, 1)), 10);
+        assert_eq!(map.pos_to_index(UVec2::new(3, 2)), 23);
+    }
+
+    #[test]
+    fn test_index_to_pos() {
+        let map = TileMap::<u8>::with_default(10, 10, 0);
+        assert_eq!(map.index_to_pos(0), UVec2::new(0, 0));
+        assert_eq!(map.index_to_pos(5), UVec2::new(5, 0));
+        assert_eq!(map.index_to_pos(10), UVec2::new(0, 1));
+        assert_eq!(map.index_to_pos(23), UVec2::new(3, 2));
+    }
+
+    #[test]
+    fn test_in_bounds() {
+        let map = TileMap::<u8>::with_default(10, 10, 0);
+        assert!(map.in_bounds(UVec2::new(0, 0)));
+        assert!(map.in_bounds(UVec2::new(9, 9)));
+        assert!(!map.in_bounds(UVec2::new(10, 0)));
+        assert!(!map.in_bounds(UVec2::new(0, 10)));
+    }
+
+    #[test]
+    fn test_get_set() {
+        let mut map = TileMap::<u8>::with_default(10, 10, 0);
+        assert_eq!(map.get(UVec2::new(5, 5)), Some(0));
+
+        assert!(map.set(UVec2::new(5, 5), 42));
+        assert_eq!(map.get(UVec2::new(5, 5)), Some(42));
+
+        assert!(!map.set(UVec2::new(10, 10), 99));
+        assert_eq!(map.get(UVec2::new(10, 10)), None);
+    }
+
+    #[test]
+    fn test_index_operators() {
+        let mut map = TileMap::<u8>::with_default(10, 10, 0);
+        map[UVec2::new(5, 5)] = 42;
+        assert_eq!(map[UVec2::new(5, 5)], 42);
+    }
+
+    #[test]
+    fn test_index_by_usize() {
+        let mut map = TileMap::<u8>::with_default(10, 10, 0);
+        map[23] = 42;
+        assert_eq!(map[23], 42);
+        assert_eq!(map[UVec2::new(3, 2)], 42);
+    }
+
+    #[test]
+    fn test_neighbors_center() {
+        let map = TileMap::<u8>::with_default(10, 10, 0);
+        let neighbors: Vec<_> = map.neighbors(UVec2::new(5, 5)).collect();
+        assert_eq!(neighbors.len(), 4);
+        assert!(neighbors.contains(&UVec2::new(5, 6)));
+        assert!(neighbors.contains(&UVec2::new(6, 5)));
+        assert!(neighbors.contains(&UVec2::new(5, 4)));
+        assert!(neighbors.contains(&UVec2::new(4, 5)));
+    }
+
+    #[test]
+    fn test_neighbors_corner() {
+        let map = TileMap::<u8>::with_default(10, 10, 0);
+        let neighbors: Vec<_> = map.neighbors(UVec2::new(0, 0)).collect();
+        assert_eq!(neighbors.len(), 2);
+        assert!(neighbors.contains(&UVec2::new(1, 0)));
+        assert!(neighbors.contains(&UVec2::new(0, 1)));
+    }
+
+    #[test]
+    fn test_neighbors_edge() {
+        let map = TileMap::<u8>::with_default(10, 10, 0);
+        let neighbors: Vec<_> = map.neighbors(UVec2::new(0, 5)).collect();
+        assert_eq!(neighbors.len(), 3);
+        assert!(neighbors.contains(&UVec2::new(0, 6)));
+        assert!(neighbors.contains(&UVec2::new(1, 5)));
+        assert!(neighbors.contains(&UVec2::new(0, 4)));
+    }
+
+    #[test]
+    fn test_on_neighbors() {
+        let map = TileMap::<u8>::with_default(10, 10, 0);
+        let mut count = 0;
+        map.on_neighbors(UVec2::new(5, 5), |_| count += 1);
+        assert_eq!(count, 4);
+    }
+
+    #[test]
+    fn test_on_neighbor_indices() {
+        let map = TileMap::<u8>::with_default(10, 10, 0);
+        let center_idx = map.pos_to_index(UVec2::new(5, 5));
+        let mut count = 0;
+        map.on_neighbor_indices(center_idx, |_| count += 1);
+        assert_eq!(count, 4);
+    }
+
+    #[test]
+    fn test_iter() {
+        let map = TileMap::<u8>::with_default(2, 2, 0);
+        let positions: Vec<_> = map.iter().map(|(pos, _)| pos).collect();
+        assert_eq!(positions.len(), 4);
+        assert!(positions.contains(&UVec2::new(0, 0)));
+        assert!(positions.contains(&UVec2::new(1, 1)));
+    }
+
+    #[test]
+    fn test_iter_values() {
+        let map = TileMap::<u8>::with_default(2, 2, 42);
+        let values: Vec<_> = map.iter_values().collect();
+        assert_eq!(values, vec![42, 42, 42, 42]);
+    }
+
+    #[test]
+    fn test_positions() {
+        let map = TileMap::<u8>::with_default(2, 2, 0);
+        let positions: Vec<_> = map.positions().collect();
+        assert_eq!(positions.len(), 4);
+        assert_eq!(positions[0], UVec2::new(0, 0));
+        assert_eq!(positions[3], UVec2::new(1, 1));
+    }
+
+    #[test]
+    fn test_enumerate() {
+        let mut map = TileMap::<u8>::with_default(2, 2, 0);
+        map[UVec2::new(1, 1)] = 42;
+        let entries: Vec<_> = map.enumerate().collect();
+        assert_eq!(entries.len(), 4);
+        assert_eq!(entries[3], (3, UVec2::new(1, 1), 42));
+    }
+
+    #[test]
+    fn test_generic_u16() {
+        let mut map = TileMap::<u16>::with_default(5, 5, 0);
+        assert_eq!(map[UVec2::new(0, 0)], 0);
+        map[UVec2::new(2, 2)] = 65535;
+        assert_eq!(map[UVec2::new(2, 2)], 65535);
+    }
+
+    #[test]
+    fn test_generic_f32() {
+        let mut map = TileMap::<f32>::with_default(5, 5, 1.5);
+        assert_eq!(map[UVec2::new(0, 0)], 1.5);
+        map[UVec2::new(2, 2)] = 2.7;
+        assert_eq!(map[UVec2::new(2, 2)], 2.7);
+    }
+}

crates/borders-core/src/game/tilemap_changes.rs

@@ -0,0 +1,179 @@
+/// Lightweight change tracking buffer for tile mutations.
+///
+/// Stores only the indices of changed tiles, avoiding allocations in the hot path
+/// by reusing Vec capacity across frames. This enables efficient delta updates
+/// for GPU rendering and network synchronization.
+///
+/// # Design
+/// - Records tile index changes as they occur
+/// - Reuses Vec capacity to avoid allocations
+/// - O(1) push, O(changes) iteration
+/// - Optional: can be cleared/ignored when tracking not needed
+///
+/// # Example
+/// ```
+/// use borders_core::game::ChangeBuffer;
+///
+/// let mut changes = ChangeBuffer::new();
+/// changes.push(10);
+/// changes.push(25);
+/// assert_eq!(changes.len(), 2);
+///
+/// let indices: Vec<_> = changes.drain().collect();
+/// assert_eq!(indices, vec![10, 25]);
+/// assert_eq!(changes.len(), 0);
+/// ```
+#[derive(Debug, Clone)]
+pub struct ChangeBuffer {
+    changed_indices: Vec<usize>,
+}
+
+impl ChangeBuffer {
+    /// Creates a new empty ChangeBuffer.
+    pub fn new() -> Self {
+        Self { changed_indices: Vec::new() }
+    }
+
+    /// Creates a new ChangeBuffer with pre-allocated capacity.
+    ///
+    /// Use this when you know the approximate number of changes to avoid reallocations.
+    pub fn with_capacity(capacity: usize) -> Self {
+        Self { changed_indices: Vec::with_capacity(capacity) }
+    }
+
+    /// Records a tile index as changed.
+    ///
+    /// Does not check for duplicates - the same index can be pushed multiple times.
+    /// Consumers should handle deduplication if needed.
+    #[inline]
+    pub fn push(&mut self, index: usize) {
+        self.changed_indices.push(index);
+    }
+
+    /// Returns an iterator over changed indices without consuming them.
+    ///
+    /// Use this when you need to read changes without clearing the buffer.
+    /// The buffer will still contain all changes after iteration.
+    pub fn iter(&self) -> impl Iterator<Item = usize> + '_ {
+        self.changed_indices.iter().copied()
+    }
+
+    /// Drains all changed indices, returning an iterator and clearing the buffer.
+    ///
+    /// The buffer retains its capacity for reuse.
+    pub fn drain(&mut self) -> impl Iterator<Item = usize> + '_ {
+        self.changed_indices.drain(..)
+    }
+
+    /// Clears all tracked changes without returning them.
+    ///
+    /// The buffer retains its capacity for reuse.
+    pub fn clear(&mut self) {
+        self.changed_indices.clear();
+    }
+
+    /// Returns true if any changes have been recorded.
+    #[inline]
+    pub fn has_changes(&self) -> bool {
+        !self.changed_indices.is_empty()
+    }
+
+    /// Returns the number of changes recorded.
+    ///
+    /// Note: This may include duplicate indices if the same tile was changed multiple times.
+    #[inline]
+    pub fn len(&self) -> usize {
+        self.changed_indices.len()
+    }
+
+    /// Returns true if no changes have been recorded.
+    #[inline]
+    pub fn is_empty(&self) -> bool {
+        self.changed_indices.is_empty()
+    }
+
+    /// Returns the current capacity of the internal buffer.
+    #[inline]
+    pub fn capacity(&self) -> usize {
+        self.changed_indices.capacity()
+    }
+}
+
+impl Default for ChangeBuffer {
+    fn default() -> Self {
+        Self::new()
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn test_new() {
+        let buffer = ChangeBuffer::new();
+        assert!(buffer.is_empty());
+        assert_eq!(buffer.len(), 0);
+    }
+
+    #[test]
+    fn test_with_capacity() {
+        let buffer = ChangeBuffer::with_capacity(100);
+        assert_eq!(buffer.capacity(), 100);
+        assert!(buffer.is_empty());
+    }
+
+    #[test]
+    fn test_push_and_drain() {
+        let mut buffer = ChangeBuffer::new();
+        buffer.push(10);
+        buffer.push(25);
+        buffer.push(42);
+
+        assert_eq!(buffer.len(), 3);
+        assert!(buffer.has_changes());
+
+        let changes: Vec<_> = buffer.drain().collect();
+        assert_eq!(changes, vec![10, 25, 42]);
+        assert!(buffer.is_empty());
+    }
+
+    #[test]
+    fn test_clear() {
+        let mut buffer = ChangeBuffer::new();
+        buffer.push(1);
+        buffer.push(2);
+        buffer.push(3);
+
+        assert_eq!(buffer.len(), 3);
+        buffer.clear();
+        assert_eq!(buffer.len(), 0);
+        assert!(buffer.is_empty());
+    }
+
+    #[test]
+    fn test_duplicate_indices() {
+        let mut buffer = ChangeBuffer::new();
+        buffer.push(10);
+        buffer.push(10);
+        buffer.push(10);
+
+        assert_eq!(buffer.len(), 3); // Does not deduplicate
+        let changes: Vec<_> = buffer.drain().collect();
+        assert_eq!(changes, vec![10, 10, 10]);
+    }
+
+    #[test]
+    fn test_capacity_retained_after_drain() {
+        let mut buffer = ChangeBuffer::with_capacity(100);
+        buffer.push(1);
+        buffer.push(2);
+
+        let initial_capacity = buffer.capacity();
+        let _: Vec<_> = buffer.drain().collect();
+
+        // Capacity should be retained after drain
+        assert!(buffer.capacity() >= initial_capacity);
+        assert!(buffer.is_empty());
+    }
+}

crates/borders-core/src/game/turn.rs

@@ -0,0 +1,34 @@
+use bevy_ecs::prelude::*;
+
+use crate::networking::Turn;
+
+/// Resource containing the current turn data
+/// Updated once per turn (10 TPS), provides turn context to all gameplay systems
+#[derive(Resource)]
+pub struct CurrentTurn {
+    pub turn: Turn,
+    /// Flag indicating if this turn has been processed by gameplay systems
+    /// Set to false when turn arrives, set to true after all systems run
+    pub processed: bool,
+}
+
+impl CurrentTurn {
+    pub fn new(turn: Turn) -> Self {
+        Self { turn, processed: false }
+    }
+
+    /// Mark turn as processed
+    pub fn mark_processed(&mut self) {
+        self.processed = true;
+    }
+
+    /// Check if turn is ready to process (not yet processed)
+    pub fn is_ready(&self) -> bool {
+        !self.processed
+    }
+}
+
+/// Run condition: only run when a turn is ready to process
+pub fn turn_is_ready(current_turn: Option<Res<CurrentTurn>>) -> bool {
+    current_turn.is_some_and(|ct| ct.is_ready())
+}

crates/borders-core/src/game/utils.rs

@@ -0,0 +1,66 @@
+/// Utility functions for tile operations
+///
+/// Call a closure for each neighbor of a tile
+///
+/// Handles boundary checks for the 4-connected grid (up, down, left, right)
+pub fn for_each_neighbor<F>(tile: usize, width: u32, height: u32, mut closure: F)
+where
+    F: FnMut(usize),
+{
+    let x = tile as u32 % width;
+    let y = tile as u32 / width;
+
+    // Left neighbor
+    if x > 0 {
+        closure(tile - 1);
+    }
+    // Right neighbor
+    if x < width - 1 {
+        closure(tile + 1);
+    }
+    // Top neighbor
+    if y > 0 {
+        closure(tile - width as usize);
+    }
+    // Bottom neighbor
+    if y < height - 1 {
+        closure(tile + width as usize);
+    }
+}
+
+/// Check if a tile has at least one neighbor matching the given predicate
+pub fn has_neighbor_owned_by(tile: usize, width: u32, height: u32, is_owner: impl Fn(usize) -> bool) -> bool {
+    let mut has_neighbor = false;
+    for_each_neighbor(tile, width, height, |neighbor| {
+        if is_owner(neighbor) {
+            has_neighbor = true;
+        }
+    });
+    has_neighbor
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn test_corner_tile_neighbors() {
+        let mut neighbors = Vec::new();
+        for_each_neighbor(0, 10, 10, |n| neighbors.push(n));
+        assert_eq!(neighbors, vec![1, 10]); // Right and down only
+    }
+
+    #[test]
+    fn test_edge_tile_neighbors() {
+        let mut neighbors = Vec::new();
+        for_each_neighbor(5, 10, 10, |n| neighbors.push(n));
+        assert_eq!(neighbors, vec![4, 6, 15]); // Left, right, and down
+    }
+
+    #[test]
+    fn test_center_tile_neighbors() {
+        let mut neighbors = Vec::new();
+        for_each_neighbor(55, 10, 10, |n| neighbors.push(n));
+        assert_eq!(neighbors, vec![54, 56, 45, 65]); // All 4 directions
+    }
+}

crates/borders-core/src/lib.rs

@@ -0,0 +1,18 @@
+pub mod app;
+pub mod build_info;
+pub mod constants;
+pub mod game;
+pub mod networking;
+pub mod platform;
+pub mod plugin;
+pub mod telemetry;
+pub mod time;
+#[cfg(feature = "ui")]
+pub mod ui;
+
+pub use constants::*;
+pub use game::*;
+pub use networking::*;
+pub use plugin::*;
+#[cfg(feature = "ui")]
+pub use ui::{LastAttacksDigest, LastLeaderboardDigest, NationHighlightState, input};

crates/borders-core/src/networking/client.rs

@@ -0,0 +1,103 @@
+use crate::networking::{GameView, Intent, IntentEvent, ProcessTurnEvent, protocol::NetMessage};
+use bevy_ecs::prelude::*;
+use flume::{Receiver, Sender};
+use tracing::{debug, error, info, warn};
+
+#[derive(Resource)]
+pub struct ClientConnection {
+    pub intent_tx: Sender<Intent>,
+    pub game_view_rx: Receiver<GameView>,
+}
+
+#[derive(Resource)]
+pub struct RemoteClientConnection {
+    pub intent_tx: Sender<NetMessage>,
+    pub net_message_rx: Receiver<NetMessage>,
+    pub player_id: Option<u16>,
+}
+
+pub fn receive_game_view_system(client: Res<ClientConnection>, mut game_view: ResMut<GameView>) {
+    while let Ok(new_view) = client.game_view_rx.try_recv() {
+        *game_view = new_view;
+    }
+}
+
+pub fn send_intent_system(mut intent_events: MessageReader<IntentEvent>, client: Res<ClientConnection>) {
+    for event in intent_events.read() {
+        debug!("Sending intent to local server: {:?}", event.0);
+        if let Err(e) = client.intent_tx.try_send(event.0.clone()) {
+            error!("Failed to send intent: {:?}", e);
+        }
+    }
+}
+
+/// System for remote clients to handle NetMessage protocol
+pub fn receive_net_message_system(remote_client: Res<RemoteClientConnection>, mut process_turn_writer: MessageWriter<ProcessTurnEvent>, mut spawn_config_writer: MessageWriter<crate::networking::SpawnConfigEvent>) {
+    let mut message_count = 0;
+    while let Ok(message) = remote_client.net_message_rx.try_recv() {
+        message_count += 1;
+        match message {
+            NetMessage::ServerConfig { player_id } => {
+                info!("Received server config: player_id={}", player_id);
+                // Store player_id in the resource (would need to make it mutable)
+            }
+            NetMessage::Turn { turn, intents } => {
+                info!("Received turn {} with {} intents", turn, intents.len());
+                // Convert to ProcessTurnEvent
+                let turn_event = ProcessTurnEvent(crate::networking::Turn { turn_number: turn, intents });
+                process_turn_writer.write(turn_event);
+            }
+            NetMessage::Intent(_) => {
+                warn!("Received Intent message on client side");
+            }
+            NetMessage::SpawnConfiguration { spawns } => {
+                info!("Received spawn configuration with {} spawns", spawns.len());
+                spawn_config_writer.write(crate::networking::SpawnConfigEvent(spawns));
+            }
+        }
+    }
+
+    if message_count > 0 {
+        let _span = tracing::debug_span!("receive_net_messages", message_count).entered();
+    }
+}
+
+/// System for remote clients to send intents as NetMessage
+pub fn send_net_intent_system(mut intent_events: MessageReader<IntentEvent>, remote_client: Res<RemoteClientConnection>) {
+    let mut intent_count = 0;
+    for event in intent_events.read() {
+        intent_count += 1;
+        let net_message = NetMessage::Intent(event.0.clone());
+        if let Err(e) = remote_client.intent_tx.try_send(net_message) {
+            error!("Failed to send net intent: {:?}", e);
+        }
+    }
+
+    if intent_count > 0 {
+        let _span = tracing::debug_span!("send_net_intents", intent_count).entered();
+    }
+}
+
+/// System to handle spawn configuration updates from server
+/// Updates local SpawnManager with remote player spawn positions
+pub fn handle_spawn_config_system(mut spawn_config_events: MessageReader<crate::networking::SpawnConfigEvent>, mut spawn_manager: Option<ResMut<crate::game::SpawnManager>>, game_instance: Option<Res<crate::game::GameInstance>>) {
+    for event in spawn_config_events.read() {
+        let Some(ref mut spawn_mgr) = spawn_manager else {
+            continue;
+        };
+        let Some(ref game_inst) = game_instance else {
+            continue;
+        };
+
+        // Update player spawns from server
+        spawn_mgr.player_spawns.clear();
+        for (&player_id, &tile_index) in &event.0 {
+            spawn_mgr.player_spawns.push((player_id as usize, tile_index as usize));
+        }
+
+        // Recalculate bot spawns based on updated player positions
+        spawn_mgr.current_bot_spawns = game_inst.bot_manager.recalculate_spawns_with_players(spawn_mgr.initial_bot_spawns.clone(), &spawn_mgr.player_spawns, &game_inst.territory_manager, spawn_mgr.rng_seed);
+
+        info!("Updated spawn manager with {} player spawns from server", spawn_mgr.player_spawns.len());
+    }
+}

crates/borders-core/src/networking/coordinator.rs

@@ -0,0 +1,189 @@
+use crate::time::Time;
+use bevy_ecs::prelude::*;
+use tracing::{debug, info, trace, warn};
+
+use crate::constants::{SPAWN_TIMEOUT_SECS, TICK_INTERVAL};
+use crate::networking::{Intent, ProcessTurnEvent, Turn};
+use flume::{Receiver, Sender};
+use std::collections::HashMap;
+use std::sync::{
+    Arc,
+    atomic::{AtomicBool, Ordering},
+};
+
+#[derive(Resource)]
+pub struct IntentReceiver {
+    pub intent_rx: Receiver<Intent>,
+}
+
+#[derive(Resource)]
+pub struct TurnReceiver {
+    pub turn_rx: Receiver<Turn>,
+}
+
+/// Local turn server control handle
+#[derive(Resource, Clone)]
+pub struct LocalTurnServerHandle {
+    pub paused: Arc<AtomicBool>,
+    pub running: Arc<AtomicBool>,
+}
+
+impl LocalTurnServerHandle {
+    pub fn pause(&self) {
+        self.paused.store(true, Ordering::SeqCst);
+    }
+
+    pub fn resume(&self) {
+        self.paused.store(false, Ordering::SeqCst);
+    }
+
+    pub fn stop(&self) {
+        self.running.store(false, Ordering::SeqCst);
+    }
+
+    pub fn is_paused(&self) -> bool {
+        self.paused.load(Ordering::SeqCst)
+    }
+
+    pub fn is_running(&self) -> bool {
+        self.running.load(Ordering::SeqCst)
+    }
+}
+
+/// Spawn timeout duration for local games (milliseconds)
+const SPAWN_TIMEOUT_MS: u64 = (SPAWN_TIMEOUT_SECS * 1000.0) as u64;
+
+/// Resource to track turn generation state
+#[derive(Resource)]
+pub struct TurnGenerator {
+    pub turn_number: u64,
+    pub accumulated_time: f64, // milliseconds
+    pub turn_tx: Sender<Turn>,
+    // Spawn phase tracking
+    pub spawn_config: HashMap<u16, u32>,
+    pub spawn_timeout_accumulated: Option<f64>, // milliseconds since first spawn
+    pub game_started: bool,
+}
+
+/// System to generate turns using Bevy's Update loop
+pub fn generate_turns_system(mut generator: ResMut<TurnGenerator>, server_handle: Res<LocalTurnServerHandle>, intent_receiver: Res<IntentReceiver>, mut spawn_manager: Option<ResMut<crate::game::SpawnManager>>, game_instance: Option<Res<crate::game::GameInstance>>, time: Res<Time>) {
+    use crate::game::GameAction;
+
+    let _span = tracing::trace_span!("generate_turns").entered();
+    if !server_handle.is_running() {
+        return;
+    }
+
+    let is_paused = server_handle.paused.load(Ordering::SeqCst);
+
+    // During spawn phase (paused), handle SetSpawn intents and track timeout
+    if is_paused {
+        // Collect SetSpawn intents during spawn phase
+        while let Ok(intent) = intent_receiver.intent_rx.try_recv() {
+            match intent {
+                Intent::SetSpawn { player_id, tile_index } => {
+                    debug!("Player {} set spawn at tile {}", player_id, tile_index);
+                    generator.spawn_config.insert(player_id, tile_index);
+
+                    // Update SpawnManager to recalculate bot positions (two-pass spawn system)
+                    if let (Some(ref mut spawn_mgr), Some(game_inst)) = (spawn_manager.as_mut(), game_instance.as_ref()) {
+                        spawn_mgr.update_player_spawn(player_id as usize, tile_index as usize, &game_inst.bot_manager, &game_inst.territory_manager);
+                    }
+
+                    // Start timeout on first spawn
+                    if generator.spawn_timeout_accumulated.is_none() {
+                        generator.spawn_timeout_accumulated = Some(0.0);
+                        debug!("Spawn timeout started ({}ms)", SPAWN_TIMEOUT_MS);
+                    }
+                }
+                Intent::Action(_) => {
+                    // Action intents during spawn phase are ignored
+                    warn!("Received Action intent during spawn phase - ignoring");
+                }
+            }
+        }
+
+        // Update spawn timeout if started
+        if let Some(ref mut accumulated) = generator.spawn_timeout_accumulated {
+            *accumulated += time.delta().as_secs_f64() * 1000.0;
+
+            // Check if timeout expired
+            if *accumulated >= SPAWN_TIMEOUT_MS as f64 {
+                debug!("Spawn timeout expired - starting game");
+
+                // Create Turn(0) with all spawn actions
+                let spawn_intents: Vec<Intent> = generator.spawn_config.iter().map(|(&player_id, &tile_index)| Intent::Action(GameAction::Spawn { player_id, tile_index })).collect();
+
+                let start_turn = Turn { turn_number: 0, intents: spawn_intents.clone() };
+
+                info!("Sending Turn(0) with {} spawns", spawn_intents.len());
+                if let Err(e) = generator.turn_tx.send(start_turn) {
+                    warn!("Failed to send Turn(0): {}", e);
+                }
+
+                // Mark game as started and clear spawn phase
+                generator.game_started = true;
+                generator.spawn_config.clear();
+                generator.spawn_timeout_accumulated = None;
+                generator.turn_number = 1; // Next turn will be turn 1
+                generator.accumulated_time = 0.0; // Reset accumulated time for clean turn timing
+
+                server_handle.resume();
+                info!("Spawn phase complete - game started, server resumed, accumulated_time reset, next turn will be Turn 1");
+            }
+        }
+
+        return;
+    }
+
+    // Normal turn generation (after game has started)
+    if !generator.game_started {
+        return; // Wait for spawn phase to complete
+    }
+
+    // Accumulate time (delta is in seconds, convert to milliseconds)
+    let delta_ms = time.delta().as_secs_f64() * 1000.0;
+    generator.accumulated_time += delta_ms;
+
+    // Only generate turn if enough time has passed
+    if generator.accumulated_time < TICK_INTERVAL as f64 {
+        return;
+    }
+
+    // Reset accumulated time
+    generator.accumulated_time -= TICK_INTERVAL as f64;
+
+    // Collect all pending Action intents (ignore SetSpawn after game starts)
+    let mut action_intents = Vec::new();
+    while let Ok(intent) = intent_receiver.intent_rx.try_recv() {
+        match intent {
+            Intent::Action(action) => {
+                action_intents.push(Intent::Action(action));
+            }
+            Intent::SetSpawn { .. } => {
+                // SetSpawn intents after game start are ignored
+                warn!("Received SetSpawn intent after game started - ignoring");
+            }
+        }
+    }
+
+    // Create turn
+    let turn = Turn { turn_number: generator.turn_number, intents: action_intents.clone() };
+
+    // Send turn
+    if let Err(e) = generator.turn_tx.send(turn) {
+        warn!("Failed to send turn {}: {}", generator.turn_number, e);
+    }
+
+    generator.turn_number += 1;
+}
+
+/// System to poll for turns from the local server and emit ProcessTurnEvent
+/// This replaces the old FixedUpdate create_turns system
+pub fn poll_turns_system(turn_receiver: Res<TurnReceiver>, mut process_turn_writer: MessageWriter<ProcessTurnEvent>) {
+    let _span = tracing::trace_span!("poll_turns").entered();
+    while let Ok(turn) = turn_receiver.turn_rx.try_recv() {
+        trace!("Received Turn {} from channel", turn.turn_number);
+        process_turn_writer.write(ProcessTurnEvent(turn));
+    }
+}

crates/borders-core/src/networking/dns.rs

@@ -0,0 +1,98 @@
+//! Custom DNS resolver using Hickory DNS with DoH/DoT support.
+//!
+//! This module provides DNS over HTTPS (DoH) functionality for enhanced privacy,
+//! with automatic fallback to system DNS if DoH is unavailable.
+
+use hickory_resolver::{
+    TokioResolver,
+    config::{NameServerConfigGroup, ResolverConfig},
+    name_server::TokioConnectionProvider,
+};
+use once_cell::sync::OnceCell;
+use std::net::SocketAddr;
+use std::sync::Arc;
+use tracing::{debug, warn};
+
+/// Custom DNS resolver for reqwest that uses Hickory DNS with DoH/DoT support.
+///
+/// This resolver is configured to use Cloudflare's DNS over HTTPS (1.1.1.1).
+/// DNS over HTTPS encrypts DNS queries, preventing eavesdropping and tampering.
+///
+/// The resolver is lazily initialized within the async context to ensure
+/// it's created within the Tokio runtime.
+#[derive(Clone, Default)]
+pub struct HickoryDnsResolver {
+    /// Lazily initialized resolver to ensure it's created within Tokio runtime context
+    state: Arc<OnceCell<TokioResolver>>,
+}
+
+impl HickoryDnsResolver {
+    pub fn new() -> Self {
+        Self { state: Arc::new(OnceCell::new()) }
+    }
+
+    /// Initialize the Hickory DNS resolver with Cloudflare DoH configuration
+    fn init_resolver() -> Result<TokioResolver, Box<dyn std::error::Error + Send + Sync>> {
+        let mut group: NameServerConfigGroup = NameServerConfigGroup::google();
+        group.merge(NameServerConfigGroup::cloudflare());
+        group.merge(NameServerConfigGroup::quad9());
+        group.merge(NameServerConfigGroup::google());
+
+        let mut config = ResolverConfig::new();
+        for server in group.iter() {
+            config.add_name_server(server.clone());
+        }
+
+        // Use tokio() constructor which properly integrates with current Tokio runtime
+        let resolver = TokioResolver::builder_with_config(config, TokioConnectionProvider::default()).build();
+
+        debug!("DNS resolver initialized with Cloudflare DoH");
+        Ok(resolver)
+    }
+}
+
+/// Fallback to system DNS when DoH is unavailable
+async fn fallback_to_system_dns(name: &str) -> Result<Box<dyn Iterator<Item = SocketAddr> + Send>, Box<dyn std::error::Error + Send + Sync>> {
+    use tokio::net::lookup_host;
+
+    let addrs: Vec<SocketAddr> = lookup_host(format!("{}:443", name))
+        .await?
+        .map(|mut addr| {
+            addr.set_port(0);
+            addr
+        })
+        .collect();
+
+    debug!("Resolved '{}' via system DNS ({} addresses)", name, addrs.len());
+    Ok(Box::new(addrs.into_iter()))
+}
+
+impl reqwest::dns::Resolve for HickoryDnsResolver {
+    fn resolve(&self, name: reqwest::dns::Name) -> reqwest::dns::Resolving {
+        let resolver_state = self.state.clone();
+        let name_str = name.as_str().to_string();
+
+        Box::pin(async move {
+            // Get or initialize the resolver within the async context (Tokio runtime)
+            let resolver = match resolver_state.get_or_try_init(Self::init_resolver) {
+                Ok(r) => r,
+                Err(e) => {
+                    warn!("Failed to initialize DoH resolver: {}, using system DNS", e);
+                    return fallback_to_system_dns(&name_str).await;
+                }
+            };
+
+            // Try Hickory DNS first (DoH)
+            match resolver.lookup_ip(format!("{}.", name_str)).await {
+                Ok(lookup) => {
+                    let addrs: reqwest::dns::Addrs = Box::new(lookup.into_iter().map(|ip| SocketAddr::new(ip, 0)));
+                    Ok(addrs)
+                }
+                Err(e) => {
+                    warn!("DoH lookup failed for '{}': {}, falling back to system DNS", name_str, e);
+                    fallback_to_system_dns(&name_str).await
+                }
+            }
+        })
+    }
+}

crates/borders-core/src/networking/mod.rs

@@ -0,0 +1,119 @@
+pub mod client;
+pub mod coordinator;
+#[cfg(not(target_arch = "wasm32"))]
+pub mod dns;
+pub mod network;
+pub mod protocol;
+pub mod server;
+
+// Re-export coordinator types for easier access
+pub use coordinator::{IntentReceiver, LocalTurnServerHandle, TurnGenerator, TurnReceiver, generate_turns_system, poll_turns_system};
+
+use bevy_ecs::prelude::{Message, Resource};
+use serde::{Deserialize, Serialize};
+use std::sync::Arc;
+
+use crate::game::action::GameAction;
+
+#[derive(Message, Debug, Clone, bincode::Encode, bincode::Decode)]
+pub struct IntentEvent(pub Intent);
+
+#[derive(Message, Debug, Clone, bincode::Encode, bincode::Decode)]
+pub struct ProcessTurnEvent(pub Turn);
+
+/// Event containing spawn configuration update from server (multiplayer)
+#[derive(Message, Debug, Clone)]
+pub struct SpawnConfigEvent(pub std::collections::HashMap<u16, u32>);
+
+/// Network wrapper for player intents
+///
+/// Intent is the network-layer representation of player intents.
+/// It has two variants:
+/// - Action: State-recorded game actions that appear in game history (replays)
+/// - SetSpawn: Ephemeral spawn selection that doesn't pollute game history
+///
+/// Note: Bot actions are NOT sent as intents - they are calculated
+/// deterministically on each client during turn execution.
+#[derive(Debug, Clone, Serialize, Deserialize, bincode::Encode, bincode::Decode)]
+pub enum Intent {
+    /// State-recorded game action (appears in game history for replays)
+    Action(GameAction),
+    /// Ephemeral spawn selection (not recorded in history)
+    /// Only valid during spawn phase, ignored after game starts
+    SetSpawn { player_id: u16, tile_index: u32 },
+}
+
+#[derive(Debug, Clone, Serialize, Deserialize, bincode::Encode, bincode::Decode)]
+pub struct Turn {
+    pub turn_number: u64,
+    pub intents: Vec<Intent>,
+}
+
+/// Read-only snapshot of game state for rendering - DETERMINISTIC, SHARED
+///
+/// **Important: This is GLOBAL/SHARED state identical across all clients!**
+///
+/// This is a read-only snapshot of GameInstance state, updated after each turn.
+/// It provides:
+/// - Safe, immutable access to game state for rendering and input systems
+/// - Serializable format for network transmission
+/// - Same view for all clients (server, players, spectators)
+///
+/// Systems should prefer using GameView over direct GameInstance access
+/// to maintain clean separation between game logic and rendering/input.
+#[derive(Resource, Default, Debug, Clone, Serialize, Deserialize, bincode::Encode, bincode::Decode)]
+pub struct GameView {
+    pub width: u32,
+    pub height: u32,
+    /// Owner of each tile. Uses Arc for zero-copy sharing with rendering.
+    pub territories: Arc<[u16]>,
+    pub players: Vec<PlayerView>,
+    pub turn_number: u64,
+    /// Total number of conquerable (non-water) tiles on the map.
+    /// Cached for performance - calculated once at initialization.
+    pub total_land_tiles: u32,
+    /// Indices of tiles that changed ownership this turn (from TerritoryManager's ChangeBuffer).
+    /// Used for efficient delta rendering without full map scans.
+    pub changed_tiles: Vec<usize>,
+    /// Active ships on the map
+    pub ships: Vec<ShipView>,
+}
+
+impl GameView {
+    /// Get the owner of a specific tile
+    pub fn get_owner(&self, tile_index: usize) -> u16 {
+        self.territories.get(tile_index).copied().unwrap_or(0)
+    }
+
+    /// Get a player by ID
+    pub fn get_player(&self, player_id: u16) -> Option<&PlayerView> {
+        self.players.iter().find(|p| p.id == player_id)
+    }
+
+    /// Find any tile owned by a specific player (useful for camera centering)
+    pub fn find_tile_owned_by(&self, player_id: u16) -> Option<usize> {
+        self.territories.iter().position(|&owner| owner == player_id)
+    }
+}
+
+#[derive(Clone, Default, Debug, Serialize, Deserialize, bincode::Encode, bincode::Decode)]
+pub struct PlayerView {
+    pub id: u16,
+    pub color: [f32; 4],
+    pub name: String,
+    pub tile_count: u32,
+    pub troops: u32,
+    pub is_alive: bool,
+}
+
+#[derive(Clone, Debug, Serialize, Deserialize, bincode::Encode, bincode::Decode)]
+pub struct ShipView {
+    pub id: u32,
+    pub owner_id: u16,
+    pub current_tile: u32,
+    pub target_tile: u32,
+    pub troops: u32,
+    pub path_progress: u32,
+    pub ticks_until_move: u32,
+    pub path: Vec<u32>,
+}

crates/borders-core/src/networking/network.rs

@@ -0,0 +1,244 @@
+use crate::networking::{GameView, Intent};
+use anyhow::Result;
+use async_trait::async_trait;
+use flume::{Receiver, Sender};
+
+#[cfg(not(target_arch = "wasm32"))]
+use crate::networking::protocol::NetMessage;
+#[cfg(not(target_arch = "wasm32"))]
+use url::Url;
+#[cfg(not(target_arch = "wasm32"))]
+use web_transport::{ClientBuilder, RecvStream, SendStream};
+
+#[async_trait]
+#[cfg_attr(target_arch = "wasm32", async_trait(?Send))]
+pub trait Transceiver: Send + Sync {
+    async fn send(&mut self, intent: Intent) -> Result<()>;
+    async fn receive(&mut self) -> Result<GameView>;
+}
+
+#[async_trait]
+#[cfg_attr(target_arch = "wasm32", async_trait(?Send))]
+pub trait ServerTransceiver: Send + Sync {
+    async fn send(&mut self, game_view: GameView) -> Result<()>;
+    async fn receive(&mut self) -> Result<Intent>;
+}
+
+#[cfg(not(target_arch = "wasm32"))]
+pub struct RemoteSender {
+    send_stream: SendStream,
+}
+
+#[cfg(not(target_arch = "wasm32"))]
+pub struct RemoteReceiver {
+    recv_stream: RecvStream,
+}
+
+pub struct RemoteConnection;
+
+#[cfg(not(target_arch = "wasm32"))]
+impl RemoteConnection {
+    /// Establishes a connection to a remote server and returns separate sender/receiver
+    pub async fn connect(server_address: &str) -> Result<(RemoteSender, RemoteReceiver)> {
+        let url = Url::parse(server_address)?;
+        let mut session = {
+            let client = ClientBuilder::new().with_system_roots()?;
+            client.connect(url).await?
+        };
+
+        let (send_stream, recv_stream) = session.open_bi().await?;
+
+        let sender = RemoteSender { send_stream };
+        let receiver = RemoteReceiver { recv_stream };
+
+        Ok((sender, receiver))
+    }
+}
+
+#[cfg(not(target_arch = "wasm32"))]
+impl RemoteSender {
+    pub async fn send(&mut self, intent: Intent) -> Result<()> {
+        let config = bincode::config::standard();
+        let bytes = bincode::encode_to_vec(intent, config)?;
+        self.send_bytes(&bytes).await
+    }
+
+    pub async fn send_net_message(&mut self, message: NetMessage) -> Result<()> {
+        let config = bincode::config::standard();
+        let bytes = bincode::encode_to_vec(message, config)?;
+        self.send_bytes(&bytes).await
+    }
+
+    async fn send_bytes(&mut self, data: &[u8]) -> Result<()> {
+        let len = data.len() as u64;
+        self.send_stream.write(&len.to_be_bytes()).await?;
+        self.send_stream.write(data).await?;
+        Ok(())
+    }
+}
+
+#[cfg(not(target_arch = "wasm32"))]
+impl RemoteReceiver {
+    pub async fn receive(&mut self) -> Result<GameView> {
+        let bytes = self.receive_bytes().await?;
+        let config = bincode::config::standard();
+        let (game_view, _) = bincode::decode_from_slice(&bytes, config)?;
+        Ok(game_view)
+    }
+
+    pub async fn receive_net_message(&mut self) -> Result<NetMessage> {
+        let bytes = self.receive_bytes().await?;
+        let config = bincode::config::standard();
+        let (net_message, _) = bincode::decode_from_slice(&bytes, config)?;
+        Ok(net_message)
+    }
+
+    async fn receive_bytes(&mut self) -> Result<Vec<u8>> {
+        // Read length prefix (8 bytes)
+        let mut len_bytes = Vec::new();
+        while len_bytes.len() < 8 {
+            let remaining = 8 - len_bytes.len();
+            if let Some(chunk) = self.recv_stream.read(remaining).await? {
+                len_bytes.extend_from_slice(&chunk);
+            } else {
+                anyhow::bail!("Stream closed before reading length prefix");
+            }
+        }
+        let len = u64::from_be_bytes(len_bytes[0..8].try_into()?) as usize;
+
+        // Read message data
+        let mut buffer = Vec::new();
+        while buffer.len() < len {
+            let remaining = len - buffer.len();
+            if let Some(chunk) = self.recv_stream.read(remaining).await? {
+                buffer.extend_from_slice(&chunk);
+            } else {
+                anyhow::bail!("Stream closed before reading full message");
+            }
+        }
+        Ok(buffer[0..len].to_vec())
+    }
+}
+
+#[cfg(not(target_arch = "wasm32"))]
+pub struct RemoteServerSender {
+    send_stream: SendStream,
+}
+
+#[cfg(not(target_arch = "wasm32"))]
+pub struct RemoteServerReceiver {
+    recv_stream: RecvStream,
+}
+
+pub struct RemoteConnectionMirror;
+
+#[cfg(not(target_arch = "wasm32"))]
+impl RemoteConnectionMirror {
+    /// Creates server-side sender/receiver from an accepted connection stream
+    pub fn from_streams(send_stream: SendStream, recv_stream: RecvStream) -> (RemoteServerSender, RemoteServerReceiver) {
+        let sender = RemoteServerSender { send_stream };
+        let receiver = RemoteServerReceiver { recv_stream };
+        (sender, receiver)
+    }
+}
+
+#[cfg(not(target_arch = "wasm32"))]
+impl RemoteServerSender {
+    pub async fn send(&mut self, game_view: GameView) -> Result<()> {
+        let config = bincode::config::standard();
+        let bytes = bincode::encode_to_vec(game_view, config)?;
+        self.send_bytes(&bytes).await
+    }
+
+    async fn send_bytes(&mut self, data: &[u8]) -> Result<()> {
+        let len = data.len() as u64;
+        self.send_stream.write(&len.to_be_bytes()).await?;
+        self.send_stream.write(data).await?;
+        Ok(())
+    }
+}
+
+#[cfg(not(target_arch = "wasm32"))]
+impl RemoteServerReceiver {
+    pub async fn receive(&mut self) -> Result<Intent> {
+        let bytes = self.receive_bytes().await?;
+        let config = bincode::config::standard();
+        let (intent, _) = bincode::decode_from_slice(&bytes, config)?;
+        Ok(intent)
+    }
+
+    async fn receive_bytes(&mut self) -> Result<Vec<u8>> {
+        // Read length prefix (8 bytes)
+        let mut len_bytes = Vec::new();
+        while len_bytes.len() < 8 {
+            let remaining = 8 - len_bytes.len();
+            if let Some(chunk) = self.recv_stream.read(remaining).await? {
+                len_bytes.extend_from_slice(&chunk);
+            } else {
+                anyhow::bail!("Stream closed before reading length prefix");
+            }
+        }
+        let len = u64::from_be_bytes(len_bytes[0..8].try_into()?) as usize;
+
+        // Read message data
+        let mut buffer = Vec::new();
+        while buffer.len() < len {
+            let remaining = len - buffer.len();
+            if let Some(chunk) = self.recv_stream.read(remaining).await? {
+                buffer.extend_from_slice(&chunk);
+            } else {
+                anyhow::bail!("Stream closed before reading full message");
+            }
+        }
+        Ok(buffer[0..len].to_vec())
+    }
+}
+
+pub struct LocalConnection {
+    pub intent_tx: Sender<Intent>,
+    pub game_view_rx: Receiver<GameView>,
+}
+
+impl LocalConnection {
+    pub fn new() -> (Self, LocalConnectionMirror) {
+        let (intent_tx, intent_rx) = flume::unbounded();
+        let (game_view_tx, game_view_rx) = flume::unbounded();
+
+        let client_end = Self { intent_tx, game_view_rx };
+
+        let server_end = LocalConnectionMirror { intent_rx, game_view_tx };
+
+        (client_end, server_end)
+    }
+}
+
+#[async_trait]
+impl Transceiver for LocalConnection {
+    async fn send(&mut self, intent: Intent) -> Result<()> {
+        self.intent_tx.send_async(intent).await?;
+        Ok(())
+    }
+
+    async fn receive(&mut self) -> Result<GameView> {
+        let game_view = self.game_view_rx.recv_async().await?;
+        Ok(game_view)
+    }
+}
+
+#[async_trait]
+impl ServerTransceiver for LocalConnectionMirror {
+    async fn send(&mut self, game_view: GameView) -> Result<()> {
+        self.game_view_tx.send_async(game_view).await?;
+        Ok(())
+    }
+
+    async fn receive(&mut self) -> Result<Intent> {
+        let intent = self.intent_rx.recv_async().await?;
+        Ok(intent)
+    }
+}
+
+pub struct LocalConnectionMirror {
+    pub intent_rx: Receiver<Intent>,
+    pub game_view_tx: Sender<GameView>,
+}

crates/borders-core/src/networking/protocol.rs

@@ -0,0 +1,23 @@
+//! Network protocol for multiplayer client-server communication
+
+use crate::networking::Intent;
+use bincode::{Decode, Encode};
+use std::collections::HashMap;
+
+/// Network message protocol for client-server communication
+#[derive(Encode, Decode, Debug, Clone)]
+pub enum NetMessage {
+    /// Server assigns player ID to client
+    ServerConfig { player_id: u16 },
+    /// Client sends intent to server
+    Intent(Intent),
+    /// Server broadcasts turn to all clients
+    Turn { turn: u64, intents: Vec<Intent> },
+    /// Server broadcasts current spawn configuration during spawn phase
+    /// Maps player_id -> tile_index for all players who have chosen spawns
+    SpawnConfiguration { spawns: HashMap<u16, u32> },
+}
+
+/// Shared constants across all binaries for deterministic behavior
+pub const NETWORK_SEED: u64 = 0xC0FFEE;
+pub const TICK_MS: u64 = 100;

crates/borders-core/src/networking/server/broadcast.rs

@@ -0,0 +1,58 @@
+use crate::game::GameInstance;
+use crate::networking::{GameView, Intent, IntentEvent, PlayerView, protocol::NetMessage};
+use bevy_ecs::prelude::*;
+use flume::Sender;
+use std::collections::HashMap;
+
+#[derive(Resource)]
+pub struct ServerChannels {
+    pub broadcast_tx: Sender<GameView>,
+    pub net_message_tx: Sender<NetMessage>,
+}
+
+pub fn broadcast_game_state_system(server_channels: Res<ServerChannels>, mut game: ResMut<GameInstance>) {
+    let game_view = create_game_view(&mut game);
+    let _ = server_channels.broadcast_tx.try_send(game_view);
+}
+
+/// System to broadcast turns to all connected clients
+pub fn broadcast_turn_system(server_channels: Res<ServerChannels>, mut turn_events: MessageReader<crate::networking::ProcessTurnEvent>) {
+    for event in turn_events.read() {
+        let turn_message = NetMessage::Turn { turn: event.0.turn_number, intents: event.0.intents.clone() };
+        let _ = server_channels.net_message_tx.try_send(turn_message);
+    }
+}
+
+/// Resource to track spawn configurations during spawn phase
+#[derive(Resource, Default)]
+pub struct SpawnConfigTracker {
+    pub spawns: HashMap<u16, u32>,
+}
+
+/// System to broadcast spawn configuration when players set their spawn
+/// Only runs during multiplayer server mode
+pub fn broadcast_spawn_config_system(mut intent_events: MessageReader<IntentEvent>, mut spawn_tracker: ResMut<SpawnConfigTracker>, server_channels: Res<ServerChannels>) {
+    for event in intent_events.read() {
+        if let Intent::SetSpawn { player_id, tile_index } = event.0 {
+            // Track this spawn
+            spawn_tracker.spawns.insert(player_id, tile_index);
+
+            // Broadcast updated spawn configuration to all clients
+            let spawn_message = NetMessage::SpawnConfiguration { spawns: spawn_tracker.spawns.clone() };
+            let _ = server_channels.net_message_tx.try_send(spawn_message);
+        }
+    }
+}
+
+fn create_game_view(game: &mut GameInstance) -> GameView {
+    use std::sync::Arc;
+
+    let total_land_tiles = game.territory_manager.as_slice().iter().filter(|ownership| !ownership.is_water()).count() as u32;
+
+    let changed_tiles: Vec<usize> = game.territory_manager.drain_changes().collect();
+
+    // Convert ships to ShipView format
+    let ships = game.ship_manager.get_ships().map(|ship| crate::networking::ShipView { id: ship.id, owner_id: ship.owner_id, current_tile: ship.get_current_tile() as u32, target_tile: ship.target_tile as u32, troops: ship.troops, path_progress: ship.current_path_index as u32, ticks_until_move: ship.ticks_per_tile.saturating_sub(ship.ticks_since_move), path: ship.path.iter().map(|&tile| tile as u32).collect() }).collect();
+
+    GameView { width: game.territory_manager.width(), height: game.territory_manager.height(), territories: Arc::from(game.territory_manager.to_u16_vec().as_slice()), turn_number: game.turn_number, total_land_tiles, changed_tiles, players: game.player_manager.get_players().iter().map(|p| PlayerView { id: p.id as u16, color: p.color.to_rgba(), name: p.name.clone(), tile_count: p.get_territory_size() as u32, troops: p.get_troops() as u32, is_alive: p.is_alive() }).collect(), ships }
+}

crates/borders-core/src/networking/server/connection_handler.rs

@@ -0,0 +1,208 @@
+#[cfg(not(target_arch = "wasm32"))]
+use crate::networking::{Intent, protocol::NetMessage, server::registry::ServerRegistry};
+#[cfg(not(target_arch = "wasm32"))]
+use anyhow::Result;
+#[cfg(not(target_arch = "wasm32"))]
+use flume::Sender;
+#[cfg(not(target_arch = "wasm32"))]
+use std::sync::Arc;
+#[cfg(not(target_arch = "wasm32"))]
+use tokio::sync::RwLock;
+#[cfg(not(target_arch = "wasm32"))]
+use tracing::{error, info, instrument, warn};
+
+#[cfg(not(target_arch = "wasm32"))]
+use web_transport::quinn::{RecvStream, SendStream, ServerBuilder};
+
+/// Handle a single client connection over WebTransport
+#[cfg(not(target_arch = "wasm32"))]
+#[instrument(skip_all)]
+pub async fn handle_client_connection(mut send_stream: SendStream, mut recv_stream: RecvStream, intent_tx: Sender<Intent>, registry: Arc<RwLock<ServerRegistry>>) -> Result<()> {
+    info!("New client connected, starting message handling");
+
+    // Create a per-client channel for receiving broadcast messages
+    let (client_tx, client_rx) = flume::unbounded::<NetMessage>();
+
+    // Register this client with the server registry and get assigned player ID
+    let player_id = { registry.write().await.add_client(client_tx) };
+    info!(player_id = player_id, "Client registered");
+
+    // Send initial server config
+    let server_config = NetMessage::ServerConfig { player_id };
+    let config_bytes = bincode::encode_to_vec(server_config, bincode::config::standard())?;
+    let len_bytes = (config_bytes.len() as u64).to_be_bytes();
+
+    // Send length prefix
+    let mut written = 0;
+    while written < len_bytes.len() {
+        let bytes_written = send_stream.write(&len_bytes[written..]).await?;
+        written += bytes_written;
+    }
+
+    // Send config bytes
+    let mut written = 0;
+    while written < config_bytes.len() {
+        let bytes_written = send_stream.write(&config_bytes[written..]).await?;
+        written += bytes_written;
+    }
+
+    // Spawn task to handle incoming intents from this client
+    let intent_tx_clone = intent_tx.clone();
+
+    tokio::spawn(async move {
+        loop {
+            // Read length prefix (8 bytes)
+            let mut len_bytes = Vec::new();
+            while len_bytes.len() < 8 {
+                let remaining = 8 - len_bytes.len();
+                if let Ok(maybe_chunk) = recv_stream.read_chunk(remaining, true).await {
+                    if let Some(chunk) = maybe_chunk {
+                        len_bytes.extend_from_slice(&chunk.bytes);
+                    } else {
+                        break;
+                    }
+                } else {
+                    error!("Stream closed before reading length prefix");
+                    break;
+                }
+            }
+            let len = u64::from_be_bytes(len_bytes[0..8].try_into().unwrap()) as usize;
+
+            // Read message data
+            let mut message_bytes = Vec::new();
+            while message_bytes.len() < len {
+                let remaining = len - message_bytes.len();
+                if let Ok(maybe_chunk) = recv_stream.read_chunk(remaining, true).await {
+                    if let Some(chunk) = maybe_chunk {
+                        message_bytes.extend_from_slice(&chunk.bytes);
+                    } else {
+                        break;
+                    }
+                } else {
+                    error!("Stream closed before reading full message");
+                    break;
+                }
+            }
+
+            // Decode message
+            match bincode::decode_from_slice(&message_bytes, bincode::config::standard()) {
+                Ok((net_message, _)) => match net_message {
+                    NetMessage::Intent(intent) => {
+                        if let Err(e) = intent_tx_clone.send(intent) {
+                            error!(error = %e, "Failed to forward intent");
+                            break;
+                        }
+                    }
+                    _ => warn!("Received unexpected message type from client"),
+                },
+                Err(e) => {
+                    error!(error = %e, "Failed to decode message");
+                    break;
+                }
+            }
+        }
+        info!("Client intent receiver task ended");
+    });
+
+    // Handle outgoing messages to this client
+    let registry_clone = registry.clone();
+    tokio::spawn(async move {
+        while let Ok(message) = client_rx.recv_async().await {
+            match bincode::encode_to_vec(message, bincode::config::standard()) {
+                Ok(message_bytes) => {
+                    let len_bytes = (message_bytes.len() as u64).to_be_bytes();
+
+                    // Send length prefix
+                    let mut written = 0;
+                    while written < len_bytes.len() {
+                        match send_stream.write(&len_bytes[written..]).await {
+                            Ok(bytes_written) => written += bytes_written,
+                            Err(e) => {
+                                error!(
+                                    player_id = player_id,
+                                    error = %e,
+                                    "Failed to send length prefix"
+                                );
+                                break;
+                            }
+                        }
+                    }
+
+                    // Send message bytes
+                    let mut written = 0;
+                    while written < message_bytes.len() {
+                        match send_stream.write(&message_bytes[written..]).await {
+                            Ok(bytes_written) => written += bytes_written,
+                            Err(e) => {
+                                error!(player_id = player_id, error = %e, "Failed to send message");
+                                break;
+                            }
+                        }
+                    }
+                }
+                Err(e) => {
+                    error!(player_id = player_id, error = %e, "Failed to encode message");
+                    break;
+                }
+            }
+        }
+        // Remove client from registry when sender task ends
+        info!(player_id = player_id, "Client message sender task ended, removing from registry");
+        registry_clone.write().await.remove_client(player_id);
+    });
+
+    info!(player_id = player_id, "Client connection handler setup complete");
+    Ok(())
+}
+
+/// Start the WebTransport server and accept connections
+#[cfg(not(target_arch = "wasm32"))]
+#[instrument(skip_all, fields(bind_address = %bind_address))]
+pub async fn start_server(bind_address: &str, intent_tx: Sender<Intent>, registry: Arc<RwLock<ServerRegistry>>) -> Result<()> {
+    info!("Starting WebTransport server");
+
+    // Load development certificate and key
+    let cert_path = "dev-cert.pem";
+    let key_path = "dev-key.pem";
+
+    let cert_data = std::fs::read(cert_path).map_err(|e| anyhow::anyhow!("Failed to read certificate file {}: {}", cert_path, e))?;
+    let key_data = std::fs::read(key_path).map_err(|e| anyhow::anyhow!("Failed to read key file {}: {}", key_path, e))?;
+
+    // Parse certificate and key
+    let certs = rustls_pemfile::certs(&mut &cert_data[..]).collect::<Result<Vec<_>, _>>().map_err(|e| anyhow::anyhow!("Failed to parse certificate: {}", e))?;
+
+    let key = rustls_pemfile::private_key(&mut &key_data[..]).map_err(|e| anyhow::anyhow!("Failed to parse private key: {}", e))?.ok_or_else(|| anyhow::anyhow!("No private key found"))?;
+
+    let mut server = ServerBuilder::new().with_addr(bind_address.parse()?).with_certificate(certs, key)?;
+    info!("WebTransport server listening for connections");
+
+    loop {
+        match server.accept().await {
+            Some(connection) => {
+                info!("New client connected");
+
+                let intent_tx_clone = intent_tx.clone();
+                let registry_clone = registry.clone();
+
+                let session = connection.ok().await?;
+
+                tokio::spawn(async move {
+                    // Accept bidirectional stream from client
+                    match session.accept_bi().await {
+                        Ok((send_stream, recv_stream)) => {
+                            if let Err(e) = handle_client_connection(send_stream, recv_stream, intent_tx_clone, registry_clone).await {
+                                error!(error = %e, "Error handling client connection");
+                            }
+                        }
+                        Err(e) => {
+                            error!(error = %e, "Failed to accept bidirectional stream from client");
+                        }
+                    }
+                });
+            }
+            None => {
+                error!("Failed to accept connection");
+            }
+        }
+    }
+}

crates/borders-core/src/networking/server/mod.rs

@@ -0,0 +1,12 @@
+//! Server components for multiplayer networking
+
+pub mod broadcast;
+pub mod connection_handler;
+pub mod registry;
+
+// Re-export commonly used types
+pub use broadcast::*;
+pub use registry::ServerRegistry;
+
+#[cfg(not(target_arch = "wasm32"))]
+pub use connection_handler::{handle_client_connection, start_server};

crates/borders-core/src/networking/server/registry.rs

@@ -0,0 +1,72 @@
+use crate::networking::protocol::NetMessage;
+use bevy_ecs::prelude::Resource;
+use flume::Sender;
+use std::collections::HashMap;
+use std::sync::{Arc, RwLock};
+use tracing::error;
+
+/// Connection information for a client
+#[derive(Debug, Clone)]
+pub struct ClientConnection {
+    pub id: u16,
+    pub tx: Sender<NetMessage>,
+}
+
+/// Registry for managing client connections and broadcasting messages
+#[derive(Resource)]
+pub struct ServerRegistry {
+    connections: Arc<RwLock<HashMap<u16, ClientConnection>>>,
+    next_player_id: Arc<RwLock<u16>>,
+}
+
+impl Default for ServerRegistry {
+    fn default() -> Self {
+        Self::new()
+    }
+}
+
+impl ServerRegistry {
+    pub fn new() -> Self {
+        Self {
+            connections: Arc::new(RwLock::new(HashMap::new())),
+            next_player_id: Arc::new(RwLock::new(1)), // Start from 1, 0 reserved
+        }
+    }
+
+    /// Add a new client connection and return assigned player ID
+    pub fn add_client(&self, tx: Sender<NetMessage>) -> u16 {
+        let mut next_id = self.next_player_id.write().unwrap();
+        let player_id = *next_id;
+        *next_id += 1;
+
+        let connection = ClientConnection { id: player_id, tx };
+        self.connections.write().unwrap().insert(player_id, connection);
+
+        player_id
+    }
+
+    /// Remove a client connection
+    pub fn remove_client(&self, player_id: u16) {
+        self.connections.write().unwrap().remove(&player_id);
+    }
+
+    /// Broadcast a message to all connected clients
+    pub fn broadcast(&self, message: NetMessage) {
+        let connections = self.connections.read().unwrap();
+        for connection in connections.values() {
+            if let Err(e) = connection.tx.send(message.clone()) {
+                error!("Failed to send message to client {}: {}", connection.id, e);
+            }
+        }
+    }
+
+    /// Get the number of connected clients
+    pub fn client_count(&self) -> usize {
+        self.connections.read().unwrap().len()
+    }
+
+    /// Get all client IDs
+    pub fn client_ids(&self) -> Vec<u16> {
+        self.connections.read().unwrap().keys().cloned().collect()
+    }
+}

crates/borders-core/src/platform.rs

@@ -0,0 +1,59 @@
+use std::future::Future;
+
+/// Spawn an async task on the appropriate runtime for the platform.
+///
+/// On native targets, uses tokio::spawn for multi-threaded execution.
+/// On WASM targets, uses wasm_bindgen_futures::spawn_local for browser integration.
+#[cfg(not(target_arch = "wasm32"))]
+pub fn spawn_task<F>(future: F)
+where
+    F: Future<Output = ()> + Send + 'static,
+{
+    tokio::spawn(future);
+}
+
+#[cfg(target_arch = "wasm32")]
+pub fn spawn_task<F>(future: F)
+where
+    F: Future<Output = ()> + 'static,
+{
+    wasm_bindgen_futures::spawn_local(future);
+}
+
+/// Spawn an async task that returns a value on the appropriate runtime.
+///
+/// On native targets, uses tokio::spawn and returns a JoinHandle.
+/// On WASM targets, uses wasm_bindgen_futures::spawn_local and immediately returns None
+/// since WASM doesn't support waiting on spawned tasks.
+#[cfg(not(target_arch = "wasm32"))]
+pub fn spawn_task_with_handle<F, T>(future: F) -> tokio::task::JoinHandle<T>
+where
+    F: Future<Output = T> + Send + 'static,
+    T: Send + 'static,
+{
+    tokio::spawn(future)
+}
+
+#[cfg(target_arch = "wasm32")]
+pub fn spawn_task_with_handle<F, T>(future: F)
+where
+    F: Future<Output = T> + 'static,
+    T: 'static,
+{
+    wasm_bindgen_futures::spawn_local(async move {
+        let _ = future.await;
+    });
+}
+
+/// Extension trait to convert any Result into anyhow::Result with string error conversion.
+///
+/// This is useful for WASM where some error types don't implement std::error::Error.
+pub trait IntoAnyhow<T> {
+    fn into_anyhow(self) -> anyhow::Result<T>;
+}
+
+impl<T, E: std::fmt::Display> IntoAnyhow<T> for Result<T, E> {
+    fn into_anyhow(self) -> anyhow::Result<T> {
+        self.map_err(|e| anyhow::anyhow!(e.to_string()))
+    }
+}

crates/borders-core/src/plugin.rs

@@ -0,0 +1,739 @@
+//! Consolidated game plugin integrating all core systems
+//!
+//! This module provides the main `GamePlugin` which sets up all game logic including:
+//! - Networking (local or remote)
+//! - Spawn phase management
+//! - Core game systems and event handling
+//! - Turn execution and processing
+
+use bevy_ecs::prelude::*;
+use bevy_ecs::schedule::common_conditions::resource_exists;
+use tracing::{debug, info, trace};
+
+use crate::app::{App, Last, Plugin, Update};
+use crate::time::{FixedTime, Time};
+
+use crate::constants::TICK_INTERVAL;
+use crate::game::{AttackControls, CurrentTurn, GameInstance, SpawnPhase, SpawnTimeout, turn_is_ready};
+use crate::networking::{
+    GameView, IntentEvent, IntentReceiver, ProcessTurnEvent, TurnReceiver,
+    coordinator::{generate_turns_system, poll_turns_system},
+};
+
+#[cfg(not(target_arch = "wasm32"))]
+use std::time::{SystemTime, UNIX_EPOCH};
+
+#[cfg(target_arch = "wasm32")]
+use web_time::{SystemTime, UNIX_EPOCH};
+
+// Re-export protocol types for convenience
+#[cfg(feature = "ui")]
+use crate::ui::protocol::{BackendMessage, CameraCommand, SpawnCountdown};
+
+/// Network mode configuration for the game
+pub enum NetworkMode {
+    /// Local single-player or hotseat mode
+    Local,
+    /// Remote multiplayer mode (non-WASM only)
+    #[cfg(not(target_arch = "wasm32"))]
+    Remote { server_address: String },
+}
+
+/// Main game plugin that consolidates all core game logic
+///
+/// This plugin sets up:
+/// - Network channels (local or remote)
+/// - Spawn phase management
+/// - Core game systems
+/// - Turn processing
+/// - Input handling
+pub struct GamePlugin {
+    pub network_mode: NetworkMode,
+}
+
+impl GamePlugin {
+    pub fn new(network_mode: NetworkMode) -> Self {
+        Self { network_mode }
+    }
+}
+
+impl Plugin for GamePlugin {
+    fn build(&self, app: &mut App) {
+        // Setup networking based on mode
+        match &self.network_mode {
+            NetworkMode::Local => {
+                info!("Initializing GamePlugin in Local mode");
+
+                // Local mode: use direct channels
+                let (intent_tx, intent_rx) = flume::unbounded();
+                let (game_view_tx, game_view_rx) = flume::unbounded();
+
+                app.insert_resource(crate::networking::client::ClientConnection { intent_tx, game_view_rx })
+                    .insert_resource(crate::networking::server::ServerChannels {
+                        broadcast_tx: game_view_tx,
+                        net_message_tx: flume::unbounded().0, // Dummy channel for local mode
+                    })
+                    .insert_resource(IntentReceiver { intent_rx })
+                    .add_systems(Update, (crate::networking::client::send_intent_system, crate::networking::client::receive_game_view_system.run_if(resource_exists::<GameView>)))
+                    .add_systems(Update, (poll_turns_system.run_if(resource_exists::<TurnReceiver>), crate::networking::server::broadcast_game_state_system.run_if(resource_exists::<GameInstance>).run_if(|spawn_phase: Option<Res<SpawnPhase>>| spawn_phase.is_none_or(|sp| !sp.active)).after(crate::game::update_player_borders_system)));
+            }
+            #[cfg(not(target_arch = "wasm32"))]
+            NetworkMode::Remote { server_address } => {
+                info!("Initializing GamePlugin in Remote mode (server: {})", server_address);
+
+                // Remote mode: use NetMessage protocol
+                let (net_intent_tx, net_intent_rx) = flume::unbounded();
+                let (net_message_tx, net_message_rx) = flume::unbounded();
+
+                app.insert_resource(crate::networking::client::RemoteClientConnection { intent_tx: net_intent_tx, net_message_rx, player_id: None }).add_systems(Update, (crate::networking::client::send_net_intent_system, crate::networking::client::receive_net_message_system, crate::networking::client::handle_spawn_config_system));
+
+                // Spawn networking thread
+                let server_addr = server_address.clone();
+                std::thread::spawn(move || {
+                    let runtime = tokio::runtime::Builder::new_current_thread().enable_all().build().unwrap();
+
+                    runtime.block_on(async move {
+                        use crate::networking::protocol::NetMessage;
+                        use tracing::error;
+
+                        info!("Connecting to remote server at {}", server_addr);
+
+                        // Load server certificate for validation
+                        let cert_path = "dev-cert.pem";
+                        let cert_data = match std::fs::read(cert_path) {
+                            Ok(data) => data,
+                            Err(e) => {
+                                error!("Failed to read certificate file {}: {}", cert_path, e);
+                                error!("Please run the `generate-dev-cert.ps1` script first.");
+                                return;
+                            }
+                        };
+
+                        let pem = pem::parse(&cert_data).expect("Failed to parse PEM certificate");
+                        let cert_hash = ring::digest::digest(&ring::digest::SHA256, pem.contents()).as_ref().to_vec();
+
+                        let client = web_transport::ClientBuilder::new().with_server_certificate_hashes(vec![cert_hash]).expect("Failed to create client with certificate hash");
+
+                        let mut connection = match client.connect(server_addr.parse().unwrap()).await {
+                            Ok(conn) => {
+                                info!("Connected to server successfully");
+                                conn
+                            }
+                            Err(e) => {
+                                error!("Failed to connect to server: {}", e);
+                                return;
+                            }
+                        };
+
+                        let (mut send_stream, mut recv_stream) = match connection.open_bi().await {
+                            Ok(streams) => {
+                                info!("Opened bidirectional stream");
+                                streams
+                            }
+                            Err(e) => {
+                                error!("Failed to open bidirectional stream: {}", e);
+                                return;
+                            }
+                        };
+
+                        // Read initial ServerConfig
+                        info!("Reading initial server config...");
+                        let mut len_bytes = Vec::new();
+                        while len_bytes.len() < 8 {
+                            let remaining = 8 - len_bytes.len();
+                            match recv_stream.read(remaining).await {
+                                Ok(Some(chunk)) => {
+                                    len_bytes.extend_from_slice(&chunk);
+                                }
+                                Ok(None) => {
+                                    error!("Stream closed before reading server config length");
+                                    return;
+                                }
+                                Err(e) => {
+                                    error!("Failed to read server config length: {}", e);
+                                    return;
+                                }
+                            }
+                        }
+
+                        let len = u64::from_be_bytes(len_bytes[0..8].try_into().unwrap()) as usize;
+
+                        let mut message_bytes = Vec::new();
+                        while message_bytes.len() < len {
+                            let remaining = len - message_bytes.len();
+                            match recv_stream.read(remaining).await {
+                                Ok(Some(chunk)) => {
+                                    message_bytes.extend_from_slice(&chunk);
+                                }
+                                Ok(None) => {
+                                    error!("Stream closed before reading server config data");
+                                    return;
+                                }
+                                Err(e) => {
+                                    error!("Failed to read server config data: {}", e);
+                                    return;
+                                }
+                            }
+                        }
+
+                        match bincode::decode_from_slice(&message_bytes, bincode::config::standard()) {
+                            Ok((net_message, _)) => {
+                                info!("Received server config: {:?}", net_message);
+                                match net_message {
+                                    NetMessage::ServerConfig { player_id } => {
+                                        info!("Assigned player ID: {}", player_id);
+                                    }
+                                    _ => {
+                                        error!("Expected ServerConfig, got: {:?}", net_message);
+                                        return;
+                                    }
+                                }
+                            }
+                            Err(e) => {
+                                error!("Failed to decode server config: {}", e);
+                                return;
+                            }
+                        }
+
+                        // Send intents to server
+                        let send_task = async {
+                            while let Ok(net_message) = net_intent_rx.recv_async().await {
+                                match bincode::encode_to_vec(net_message, bincode::config::standard()) {
+                                    Ok(message_bytes) => {
+                                        let len_bytes = (message_bytes.len() as u64).to_be_bytes();
+
+                                        let mut written = 0;
+                                        while written < len_bytes.len() {
+                                            match send_stream.write(&len_bytes[written..]).await {
+                                                Ok(bytes_written) => written += bytes_written,
+                                                Err(e) => {
+                                                    error!("Failed to send length prefix: {}", e);
+                                                    return;
+                                                }
+                                            }
+                                        }
+
+                                        let mut written = 0;
+                                        while written < message_bytes.len() {
+                                            match send_stream.write(&message_bytes[written..]).await {
+                                                Ok(bytes_written) => written += bytes_written,
+                                                Err(e) => {
+                                                    error!("Failed to send message: {}", e);
+                                                    return;
+                                                }
+                                            }
+                                        }
+                                    }
+                                    Err(e) => {
+                                        error!("Failed to encode message: {}", e);
+                                        break;
+                                    }
+                                }
+                            }
+                        };
+
+                        // Receive messages from server
+                        let recv_task = async {
+                            loop {
+                                let mut len_bytes = Vec::new();
+                                while len_bytes.len() < 8 {
+                                    let remaining = 8 - len_bytes.len();
+                                    if let Ok(maybe_chunk) = recv_stream.read(remaining).await {
+                                        if let Some(chunk) = maybe_chunk {
+                                            len_bytes.extend_from_slice(&chunk);
+                                        } else {
+                                            break;
+                                        }
+                                    } else {
+                                        error!("Stream closed before reading length prefix");
+                                        break;
+                                    }
+                                }
+                                let len = u64::from_be_bytes(len_bytes[0..8].try_into().unwrap()) as usize;
+
+                                let mut message_bytes = Vec::new();
+                                while message_bytes.len() < len {
+                                    let remaining = len - message_bytes.len();
+                                    if let Ok(maybe_chunk) = recv_stream.read(remaining).await {
+                                        if let Some(chunk) = maybe_chunk {
+                                            message_bytes.extend_from_slice(&chunk);
+                                        } else {
+                                            break;
+                                        }
+                                    } else {
+                                        error!("Stream closed before reading full message");
+                                        break;
+                                    }
+                                }
+
+                                match bincode::decode_from_slice(&message_bytes, bincode::config::standard()) {
+                                    Ok((net_message, _)) => {
+                                        if net_message_tx.send_async(net_message).await.is_err() {
+                                            error!("Failed to forward message to client");
+                                            break;
+                                        }
+                                    }
+                                    Err(e) => {
+                                        error!("Failed to decode message: {}", e);
+                                        break;
+                                    }
+                                }
+                            }
+                        };
+
+                        futures_lite::future::zip(send_task, recv_task).await;
+                        error!("Connection to server closed");
+                    });
+                });
+            }
+        }
+
+        // Configure fixed timestep for game logic (10 TPS = 100ms)
+        app.insert_resource(FixedTime::from_seconds(TICK_INTERVAL as f64 / 1000.0));
+
+        // Core multiplayer events and resources
+        app.add_message::<IntentEvent>().add_message::<ProcessTurnEvent>().add_message::<crate::networking::SpawnConfigEvent>().init_resource::<GameView>();
+
+        // UI-related events and resources (feature-gated)
+        #[cfg(feature = "ui")]
+        {
+            app.add_message::<CameraCommand>().init_resource::<crate::ui::LastLeaderboardDigest>().init_resource::<crate::ui::LastAttacksDigest>().init_resource::<crate::ui::LeaderboardThrottle>().init_resource::<crate::ui::NationHighlightState>().init_resource::<crate::ui::ShipStateTracker>();
+        }
+
+        // Input-related resources
+        app.init_resource::<SpawnPhase>().init_resource::<AttackControls>();
+
+        // Spawn phase management
+        app.init_resource::<SpawnPhaseInitialized>().init_resource::<PreviousSpawnState>().add_systems(Update, (emit_initial_spawn_phase_system.run_if(resource_exists::<SpawnPhase>), manage_spawn_phase_system, update_spawn_preview_system.run_if(resource_exists::<SpawnPhase>)));
+
+        // Core game logic systems (run in Update, event-driven)
+        app.add_systems(
+            Update,
+            (
+                // Step 1: Receive turn events and update CurrentTurn resource
+                update_current_turn_system,
+                // Step 2: Execute gameplay systems only when turn is ready (10 TPS)
+                (crate::game::process_player_income_system, execute_turn_gameplay_system, crate::game::update_player_borders_system, crate::game::check_local_player_outcome)
+                    .chain() // Ensure income runs before turn execution
+                    .run_if(turn_is_ready)
+                    .run_if(resource_exists::<GameInstance>)
+                    .run_if(resource_exists::<GameView>)
+                    .run_if(resource_exists::<SpawnPhase>),
+            )
+                .chain(), // Ensure update_current_turn_system completes before execution systems
+        );
+
+        // UI update systems (feature-gated)
+        #[cfg(feature = "ui")]
+        app.add_systems(Update, (crate::ui::emit_leaderboard_snapshot_system, crate::ui::emit_attacks_update_system, crate::ui::emit_ships_update_system, crate::ui::emit_nation_highlight_system).run_if(resource_exists::<GameInstance>).run_if(resource_exists::<GameView>));
+
+        // Command handlers
+        #[cfg(feature = "ui")]
+        app.add_systems(Update, handle_frontend_messages_system);
+
+        // Platform-agnostic input systems
+        app.add_systems(Update, (crate::game::handle_spawn_click_system, crate::game::handle_attack_click_system, crate::game::handle_center_camera_system, crate::game::handle_attack_ratio_keys_system).run_if(resource_exists::<GameInstance>));
+
+        // Input state frame update
+        app.add_systems(Last, clear_input_state_system);
+
+        // Turn generation system
+        app.add_systems(Update, generate_turns_system.run_if(resource_exists::<crate::networking::TurnGenerator>));
+    }
+}
+
+/// Resource to track if we've emitted the initial spawn phase event
+#[derive(Resource, Default)]
+struct SpawnPhaseInitialized {
+    emitted_initial: bool,
+}
+
+/// Resource to track previous spawn state for incremental updates
+#[derive(Resource, Default)]
+struct PreviousSpawnState {
+    spawns: Vec<(usize, usize)>, // (player_id, tile_index)
+}
+
+/// System to emit initial SpawnPhaseUpdate when game starts
+#[cfg(feature = "ui")]
+fn emit_initial_spawn_phase_system(mut initialized: ResMut<SpawnPhaseInitialized>, spawn_phase: Res<SpawnPhase>, game_instance: Option<Res<GameInstance>>, mut backend_messages: MessageWriter<BackendMessage>) {
+    if initialized.emitted_initial || !spawn_phase.active || game_instance.is_none() {
+        return;
+    }
+
+    backend_messages.write(BackendMessage::SpawnPhaseUpdate { countdown: None });
+    initialized.emitted_initial = true;
+    debug!("Emitted initial SpawnPhaseUpdate (no countdown)");
+}
+
+#[cfg(not(feature = "ui"))]
+fn emit_initial_spawn_phase_system() {}
+
+/// System to manage spawn timeout and emit countdown updates
+#[cfg(feature = "ui")]
+fn manage_spawn_phase_system(mut spawn_timeout: Option<ResMut<SpawnTimeout>>, spawn_phase: Option<Res<SpawnPhase>>, time: Res<Time>, mut backend_messages: MessageWriter<BackendMessage>) {
+    let Some(spawn_phase) = spawn_phase else {
+        return;
+    };
+
+    let Some(ref mut spawn_timeout) = spawn_timeout else {
+        return;
+    };
+
+    if !spawn_phase.active || !spawn_timeout.active {
+        return;
+    }
+
+    spawn_timeout.update(time.delta_secs());
+
+    let started_at_ms = SystemTime::now().duration_since(UNIX_EPOCH).unwrap().as_millis() as u64 - (spawn_timeout.elapsed_secs * 1000.0) as u64;
+
+    backend_messages.write(BackendMessage::SpawnPhaseUpdate { countdown: Some(SpawnCountdown { started_at_ms, duration_secs: spawn_timeout.duration_secs }) });
+
+    trace!("SpawnPhaseUpdate: remaining {:.1}s", spawn_timeout.remaining_secs);
+}
+
+#[cfg(not(feature = "ui"))]
+fn manage_spawn_phase_system() {}
+
+/// System to update GameView with spawn preview during spawn phase
+/// This shows territory data to the frontend BEFORE Turn(0) is executed
+/// Only processes changed spawns incrementally for better performance
+fn update_spawn_preview_system(spawn_phase: Res<SpawnPhase>, spawn_manager: Option<Res<crate::game::SpawnManager>>, mut game_view: Option<ResMut<GameView>>, game_instance: Option<Res<GameInstance>>, mut previous_state: ResMut<PreviousSpawnState>) {
+    if !spawn_phase.active {
+        return;
+    }
+
+    let Some(ref spawn_mgr) = spawn_manager else {
+        return;
+    };
+
+    // Only update if SpawnManager has changed
+    if !spawn_mgr.is_changed() {
+        return;
+    }
+
+    let Some(ref mut game_view) = game_view else {
+        return;
+    };
+
+    let Some(ref game_inst) = game_instance else {
+        return;
+    };
+
+    let width = game_view.width;
+    let height = game_view.height;
+
+    // Get current spawns
+    let current_spawns = spawn_mgr.get_all_spawns();
+
+    // Find spawns that were removed and added
+    let previous_spawns = &previous_state.spawns;
+    let removed_spawns: Vec<_> = previous_spawns.iter().filter(|prev| !current_spawns.contains(prev)).copied().collect();
+    let added_spawns: Vec<_> = current_spawns.iter().filter(|curr| !previous_spawns.contains(curr)).copied().collect();
+
+    // If nothing changed, return early
+    if removed_spawns.is_empty() && added_spawns.is_empty() {
+        return;
+    }
+
+    // Clone territories only if we have changes to process
+    use std::sync::Arc;
+    let old_territories: Vec<crate::game::TileOwnership> = game_view.territories.iter().map(|&u| crate::game::TileOwnership::from_u16(u)).collect();
+    let mut territories = old_territories.clone();
+    let base_territories = game_inst.territory_manager.as_slice();
+    let mut changed_tiles = std::collections::HashSet::new();
+
+    // Process removed spawns: revert their 5x5 areas to base state
+    for &(player_id, tile_index) in &removed_spawns {
+        let spawn_x = tile_index as u32 % width;
+        let spawn_y = tile_index as u32 / width;
+
+        for dy in -2..=2 {
+            for dx in -2..=2 {
+                let x = (spawn_x as i32 + dx).clamp(0, width as i32 - 1) as u32;
+                let y = (spawn_y as i32 + dy).clamp(0, height as i32 - 1) as u32;
+                let idx = (x + y * width) as usize;
+
+                // Check if this tile belongs to the removed spawn
+                if territories[idx].is_owned_by(player_id as u16) {
+                    // Recalculate from scratch for this tile
+                    let mut new_owner = base_territories[idx];
+
+                    // Check if any other spawn claims this tile
+                    for &(other_player_id, other_tile_index) in &current_spawns {
+                        let other_x = other_tile_index as u32 % width;
+                        let other_y = other_tile_index as u32 / width;
+                        let dx_other = x as i32 - other_x as i32;
+                        let dy_other = y as i32 - other_y as i32;
+
+                        if dx_other.abs() <= 2 && dy_other.abs() <= 2 && base_territories[idx].is_unclaimed() {
+                            new_owner = crate::game::TileOwnership::Owned(other_player_id as u16);
+                            break;
+                        }
+                    }
+
+                    if territories[idx] != new_owner {
+                        territories[idx] = new_owner;
+                        changed_tiles.insert(idx);
+                    }
+                }
+            }
+        }
+    }
+
+    // Process added spawns: mark their 5x5 areas
+    for &(player_id, tile_index) in &added_spawns {
+        let spawn_x = tile_index as u32 % width;
+        let spawn_y = tile_index as u32 / width;
+
+        for dy in -2..=2 {
+            for dx in -2..=2 {
+                let x = (spawn_x as i32 + dx).clamp(0, width as i32 - 1) as u32;
+                let y = (spawn_y as i32 + dy).clamp(0, height as i32 - 1) as u32;
+                let idx = (x + y * width) as usize;
+
+                // Only claim if base territory is unclaimed
+                if base_territories[idx].is_unclaimed() {
+                    let old_value = territories[idx];
+                    let new_owner = crate::game::TileOwnership::Owned(player_id as u16);
+                    if old_value != new_owner {
+                        territories[idx] = new_owner;
+                        changed_tiles.insert(idx);
+                    }
+                }
+            }
+        }
+    }
+
+    // Convert back to u16 and update game view
+    let territories_u16: Vec<u16> = territories.iter().map(|o| o.to_u16()).collect();
+    game_view.territories = Arc::from(territories_u16.as_slice());
+    game_view.changed_tiles = changed_tiles.into_iter().collect();
+
+    // Update player tile counts incrementally by tracking deltas from changed tiles
+    // This is O(changed_tiles) instead of O(total_tiles) = ~100 ops instead of 6.5M ops
+    let mut players_map = std::collections::HashMap::new();
+    for player in &game_view.players {
+        players_map.insert(player.id, player.clone());
+    }
+
+    // Track tile count changes per player
+    let mut tile_deltas: std::collections::HashMap<u16, i32> = std::collections::HashMap::new();
+
+    // For each changed tile, update the delta counters
+    for &idx in &game_view.changed_tiles {
+        let old_owner = old_territories[idx];
+        let new_owner = territories[idx];
+
+        // Decrement count for previous owner (if any)
+        if let crate::game::TileOwnership::Owned(old_owner_id) = old_owner
+            && old_owner_id != 0
+        {
+            *tile_deltas.entry(old_owner_id).or_insert(0) -= 1;
+        }
+
+        // Increment count for new owner (if any)
+        if let crate::game::TileOwnership::Owned(new_owner_id) = new_owner
+            && new_owner_id != 0
+        {
+            *tile_deltas.entry(new_owner_id).or_insert(0) += 1;
+        }
+    }
+
+    // Apply deltas to player tile counts
+    for (player_id, delta) in tile_deltas {
+        if let Some(player) = players_map.get_mut(&player_id) {
+            player.tile_count = (player.tile_count as i32 + delta).max(0) as u32;
+        }
+    }
+
+    game_view.players = players_map.into_values().collect();
+
+    // Update previous state
+    previous_state.spawns = current_spawns.clone();
+
+    trace!("Spawn preview updated: {} removed, {} added, {} changed tiles", removed_spawns.len(), added_spawns.len(), game_view.changed_tiles.len());
+}
+
+/// System to clear per-frame input state data
+fn clear_input_state_system(input: Option<NonSend<std::sync::Arc<std::sync::Mutex<crate::ui::input::InputState>>>>) {
+    if let Some(input) = input
+        && let Ok(mut state) = input.lock()
+    {
+        state.clear_frame_data();
+    }
+}
+
+/// System to receive turn events and update CurrentTurn resource
+pub fn update_current_turn_system(mut turn_events: MessageReader<ProcessTurnEvent>, mut current_turn: Option<ResMut<CurrentTurn>>, mut commands: Commands) {
+    // Read all turn events (should only be one per frame at 10 TPS)
+    let turns: Vec<_> = turn_events.read().map(|e| e.0.clone()).collect();
+
+    if turns.is_empty() {
+        return;
+    }
+
+    // Take the latest turn (in case multiple arrived, though this shouldn't happen)
+    let turn = turns.into_iter().last().unwrap();
+
+    trace!("Received turn {} with {} intents", turn.turn_number, turn.intents.len());
+
+    if let Some(ref mut current_turn_res) = current_turn {
+        // Update existing resource
+        current_turn_res.turn = turn;
+        current_turn_res.processed = false; // Mark as ready for processing
+    } else {
+        // Initialize resource on first turn
+        commands.insert_resource(CurrentTurn::new(turn));
+    }
+}
+
+/// Execute turn gameplay logic
+/// Only runs when turn_is_ready() returns true (once per turn at 10 TPS)
+pub fn execute_turn_gameplay_system(mut current_turn: ResMut<CurrentTurn>, mut game_instance: ResMut<GameInstance>, mut game_view: Option<ResMut<GameView>>, spawn_manager: Option<Res<crate::game::SpawnManager>>, mut spawn_phase: ResMut<SpawnPhase>, #[cfg(feature = "ui")] mut backend_messages: MessageWriter<BackendMessage>, server_handle: Option<Res<crate::networking::LocalTurnServerHandle>>) {
+    use std::sync::Arc;
+
+    let Some(ref mut game_view) = game_view else {
+        return;
+    };
+
+    let turn = &current_turn.turn;
+
+    trace!("Executing turn {} with {} intents", turn.turn_number, turn.intents.len());
+
+    game_instance.execute_turn(turn);
+
+    if turn.turn_number == 0
+        && let Some(ref spawn_mgr) = spawn_manager
+    {
+        let bot_spawns = spawn_mgr.get_bot_spawns();
+        for &(player_id, tile_index) in bot_spawns {
+            game_instance.handle_spawn(player_id as u16, tile_index as u32);
+        }
+    }
+
+    let total_land_tiles = game_instance.territory_manager.as_slice().iter().filter(|ownership| !ownership.is_water()).count() as u32;
+
+    // Convert ships to ShipView format
+    let ships = game_instance.ship_manager.get_ships().map(|ship| crate::networking::ShipView { id: ship.id, owner_id: ship.owner_id, current_tile: ship.get_current_tile() as u32, target_tile: ship.target_tile as u32, troops: ship.troops, path_progress: ship.current_path_index as u32, ticks_until_move: ship.ticks_per_tile.saturating_sub(ship.ticks_since_move), path: ship.path.iter().map(|&tile| tile as u32).collect() }).collect();
+
+    **game_view = GameView { width: game_instance.territory_manager.width(), height: game_instance.territory_manager.height(), territories: Arc::from(game_instance.territory_manager.to_u16_vec().as_slice()), turn_number: game_instance.turn_number, total_land_tiles, changed_tiles: Vec::new(), players: game_instance.player_manager.get_players().iter().map(|p| crate::networking::PlayerView { id: p.id as u16, color: p.color.to_rgba(), name: p.name.clone(), tile_count: p.get_territory_size() as u32, troops: p.get_troops() as u32, is_alive: p.is_alive() }).collect(), ships };
+
+    trace!("GameView updated: turn {}, {} players", game_view.turn_number, game_view.players.len());
+
+    if turn.turn_number == 0 && spawn_phase.active {
+        spawn_phase.active = false;
+
+        #[cfg(feature = "ui")]
+        backend_messages.write(BackendMessage::SpawnPhaseEnded);
+
+        info!("Spawn phase ended after Turn(0) execution");
+
+        if let Some(ref handle) = server_handle {
+            handle.resume();
+            info!("Local turn server resumed - game started");
+        }
+    }
+
+    // Mark turn as processed to prevent re-execution
+    current_turn.mark_processed();
+}
+
+/// System to handle FrontendMessage events
+#[cfg(feature = "ui")]
+#[allow(clippy::too_many_arguments)]
+fn handle_frontend_messages_system(mut commands: Commands, mut frontend_messages: MessageReader<crate::ui::protocol::FrontendMessage>, game_instance: Option<Res<GameInstance>>, intent_receiver: Option<Res<IntentReceiver>>, mut attack_controls: Option<ResMut<AttackControls>>, mut spawn_phase: ResMut<SpawnPhase>, mut spawn_phase_init: ResMut<SpawnPhaseInitialized>, mut previous_spawn_state: ResMut<PreviousSpawnState>) {
+    use crate::ui::protocol::FrontendMessage;
+    use tracing::{debug, error, info};
+
+    for message in frontend_messages.read() {
+        match message {
+            FrontendMessage::StartGame => {
+                info!("Processing StartGame command");
+
+                if game_instance.is_some() {
+                    error!("Game already running - ignoring StartGame");
+                    continue;
+                }
+
+                let Some(ref intent_receiver) = intent_receiver else {
+                    error!("IntentReceiver not available - cannot start game");
+                    continue;
+                };
+
+                let terrain_data = match crate::game::TerrainData::load_world_map() {
+                    Ok(data) => data,
+                    Err(e) => {
+                        error!("Failed to load World map: {}", e);
+                        continue;
+                    }
+                };
+
+                let terrain_arc = std::sync::Arc::new(terrain_data.clone());
+                commands.insert_resource(terrain_data);
+
+                let size = terrain_arc.size();
+                let width = size.x;
+                let height = size.y;
+                let mut conquerable_tiles = Vec::with_capacity((width * height) as usize);
+
+                for y in 0..height {
+                    for x in 0..width {
+                        conquerable_tiles.push(terrain_arc.is_conquerable((x, y)));
+                    }
+                }
+
+                let params = crate::game::GameInitParams {
+                    map_width: width,
+                    map_height: height,
+                    conquerable_tiles,
+                    client_player_id: 0, // Human player is ID 0
+                    intent_rx: intent_receiver.intent_rx.clone(),
+                    terrain_data: terrain_arc,
+                };
+
+                crate::game::initialize_game_resources(&mut commands, params);
+                info!("Game initialized successfully");
+            }
+
+            FrontendMessage::QuitGame => {
+                info!("Processing QuitGame command");
+                if game_instance.is_some() {
+                    // Remove all game-specific resources
+                    commands.remove_resource::<GameInstance>();
+                    commands.remove_resource::<crate::game::LocalPlayerContext>();
+                    commands.remove_resource::<TurnReceiver>();
+                    commands.remove_resource::<crate::game::SpawnManager>();
+                    commands.remove_resource::<crate::game::SpawnTimeout>();
+                    commands.remove_resource::<GameView>();
+                    commands.remove_resource::<crate::TerrainData>();
+                    commands.remove_resource::<crate::networking::TurnGenerator>();
+
+                    // Reset permanent resources to default state
+                    spawn_phase.active = false;
+                    spawn_phase_init.emitted_initial = false;
+                    previous_spawn_state.spawns.clear();
+
+                    // Note: LocalTurnServerHandle cleanup requires World access
+                    // It will be cleaned up automatically when the resource is dropped
+
+                    info!("Game stopped and resources cleaned up");
+                }
+            }
+
+            FrontendMessage::PauseGame | FrontendMessage::ResumeGame => {
+                // TODO: Implement pause/resume functionality
+            }
+
+            FrontendMessage::SetAttackRatio { ratio } => {
+                if let Some(ref mut controls) = attack_controls {
+                    controls.attack_ratio = ratio.clamp(0.01, 1.0);
+                    debug!("Attack ratio set to {:.1}%", controls.attack_ratio * 100.0);
+                }
+            }
+
+            _ => {}
+        }
+    }
+}

crates/borders-core/src/telemetry/client.rs

@@ -0,0 +1,311 @@
+use super::types::{BatchCaptureRequest, BatchEvent, TelemetryConfig, TelemetryEvent};
+use super::user_id::UserIdType;
+use crate::platform::spawn_task;
+use futures::lock::Mutex;
+use hmac::{Hmac, Mac};
+use sha2::Sha256;
+use std::collections::HashMap;
+use std::error::Error;
+use std::sync::Arc;
+use tracing::{debug, error, warn};
+
+#[cfg(not(target_arch = "wasm32"))]
+use super::user_id::get_or_create_user_id;
+
+type HmacSha256 = Hmac<Sha256>;
+
+/// Build an HTTP client with appropriate DNS resolver for the platform.
+///
+/// On non-WASM targets, attempts to use Hickory DNS with DoH support.
+/// Falls back to default client if DoH initialization fails.
+#[cfg(not(target_arch = "wasm32"))]
+fn build_http_client() -> reqwest::Client {
+    match reqwest::Client::builder().dns_resolver(Arc::new(crate::networking::dns::HickoryDnsResolver::new())).build() {
+        Ok(client) => {
+            debug!("HTTP client initialized with DoH resolver");
+            client
+        }
+        Err(e) => {
+            warn!("Failed to build HTTP client with DoH: {}, using default", e);
+            reqwest::Client::new()
+        }
+    }
+}
+
+#[cfg(target_arch = "wasm32")]
+fn build_http_client() -> reqwest::Client {
+    reqwest::Client::new()
+}
+
+/// A simple telemetry client that batches events and sends them to PostHog.
+///
+/// This client works on both native and WASM targets by using reqwest
+/// with appropriate feature flags.
+#[derive(Clone)]
+pub struct TelemetryClient {
+    config: TelemetryConfig,
+    client: reqwest::Client,
+    /// Distinct ID for this client instance (anonymous user ID)
+    distinct_id: String,
+    /// Lightweight properties attached to every event
+    default_properties: HashMap<String, serde_json::Value>,
+    /// Event buffer for batching
+    buffer: Arc<Mutex<Vec<TelemetryEvent>>>,
+    /// Whether the flush task has been started
+    flush_task_started: Arc<std::sync::atomic::AtomicBool>,
+    /// Track in-flight batch sends (native only)
+    #[cfg(not(target_arch = "wasm32"))]
+    in_flight_sends: Arc<tokio::sync::Mutex<Vec<tokio::task::JoinHandle<()>>>>,
+}
+
+impl TelemetryClient {
+    /// Create a new telemetry client with the given configuration.
+    #[cfg(not(target_arch = "wasm32"))]
+    pub fn new(config: TelemetryConfig) -> Self {
+        let (distinct_id, id_type) = get_or_create_user_id();
+        debug!("Telemetry client initialized (user ID type: {})", id_type.as_str());
+
+        let default_properties = build_default_properties(id_type);
+
+        Self { config, client: build_http_client(), distinct_id, default_properties, buffer: Arc::new(Mutex::new(Vec::new())), flush_task_started: Arc::new(std::sync::atomic::AtomicBool::new(false)), in_flight_sends: Arc::new(tokio::sync::Mutex::new(Vec::new())) }
+    }
+
+    /// Create a new telemetry client with a pre-loaded user ID.
+    ///
+    /// This is used on WASM where user ID loading is async.
+    pub fn new_with_user_id(config: TelemetryConfig, distinct_id: String, id_type: UserIdType) -> Self {
+        debug!("Telemetry client initialized (user ID type: {})", id_type.as_str());
+
+        let default_properties = build_default_properties(id_type);
+
+        Self {
+            config,
+            client: build_http_client(),
+            distinct_id,
+            default_properties,
+            buffer: Arc::new(Mutex::new(Vec::new())),
+            flush_task_started: Arc::new(std::sync::atomic::AtomicBool::new(false)),
+            #[cfg(not(target_arch = "wasm32"))]
+            in_flight_sends: Arc::new(tokio::sync::Mutex::new(Vec::new())),
+        }
+    }
+
+    /// Start a background task that periodically flushes events.
+    /// This ensures events are sent even if the batch size isn't reached.
+    ///
+    /// Only starts once, subsequent calls are no-ops.
+    fn ensure_flush_task_started(&self) {
+        // Check if already started (fast path)
+        if self.flush_task_started.load(std::sync::atomic::Ordering::Acquire) {
+            return;
+        }
+
+        // Try to start the task (only one thread will succeed)
+        if self.flush_task_started.compare_exchange(false, true, std::sync::atomic::Ordering::AcqRel, std::sync::atomic::Ordering::Acquire).is_err() {
+            // Another thread beat us to it
+            return;
+        }
+
+        // We won the race, start the task
+        let client = self.clone();
+        let interval_secs = self.config.flush_interval_secs;
+
+        spawn_task(async move {
+            #[cfg(not(target_arch = "wasm32"))]
+            {
+                let mut interval = tokio::time::interval(std::time::Duration::from_secs(interval_secs));
+                loop {
+                    interval.tick().await;
+                    client.flush().await;
+                }
+            }
+            #[cfg(target_arch = "wasm32")]
+            {
+                use gloo_timers::future::TimeoutFuture;
+                loop {
+                    TimeoutFuture::new((interval_secs * 1000) as u32).await;
+                    client.flush().await;
+                }
+            }
+        });
+        debug!("Started periodic flush task (interval: {}s)", interval_secs);
+    }
+
+    /// Track a telemetry event. Events are buffered and sent in batches.
+    pub async fn track(&self, event: TelemetryEvent) {
+        // Ensure the periodic flush task is running (lazy start)
+        self.ensure_flush_task_started();
+
+        debug!("Buffering telemetry event: {}", event.event);
+
+        let mut buffer = self.buffer.lock().await;
+        buffer.push(event);
+
+        // Check if we should flush based on batch size
+        if buffer.len() >= self.config.batch_size {
+            debug!("Batch size reached ({}), flushing events", buffer.len());
+            let events_to_send = buffer.drain(..).collect::<Vec<_>>();
+            drop(buffer); // Release lock before async operation
+
+            // Spawn a task to send in the background (non-blocking)
+            let client = self.clone();
+
+            #[cfg(not(target_arch = "wasm32"))]
+            {
+                let handle = tokio::spawn(async move {
+                    client.send_batch(events_to_send).await;
+                });
+                // Track the in-flight send and clean up completed tasks
+                let mut in_flight = self.in_flight_sends.lock().await;
+                in_flight.retain(|h| !h.is_finished());
+                in_flight.push(handle);
+            }
+
+            #[cfg(target_arch = "wasm32")]
+            spawn_task(async move {
+                client.send_batch(events_to_send).await;
+            });
+        }
+    }
+
+    /// Manually flush all buffered events.
+    ///
+    /// This method waits for all in-flight sends to complete, then sends any remaining buffered events.
+    pub async fn flush(&self) {
+        // First, wait for all in-flight background sends to complete
+        #[cfg(not(target_arch = "wasm32"))]
+        {
+            let handles = {
+                let mut in_flight = self.in_flight_sends.lock().await;
+                in_flight.drain(..).collect::<Vec<_>>()
+            };
+
+            if !handles.is_empty() {
+                debug!("Waiting for {} in-flight batch sends to complete", handles.len());
+                for handle in handles {
+                    let _ = handle.await;
+                }
+            }
+        }
+
+        // Then flush any remaining buffered events
+        let events_to_send = {
+            let mut buffer = self.buffer.lock().await;
+
+            if buffer.is_empty() {
+                return;
+            }
+
+            let events = buffer.drain(..).collect::<Vec<_>>();
+            debug!("Flushing {} buffered events", events.len());
+            events
+        };
+
+        // Send synchronously (wait for completion)
+        self.send_batch(events_to_send).await;
+    }
+
+    /// Generate HMAC-SHA256 signature for request payload.
+    ///
+    /// This prevents tampering and verifies request integrity.
+    fn sign_payload(&self, payload: &[u8]) -> String {
+        let mut mac = HmacSha256::new_from_slice(self.config.signing_key.as_bytes()).expect("HMAC can take key of any size");
+        mac.update(payload);
+
+        // Convert to hex string
+        let result = mac.finalize();
+        let bytes = result.into_bytes();
+        hex::encode(bytes)
+    }
+
+    /// Send a batch of events to PostHog.
+    async fn send_batch(&self, events: Vec<TelemetryEvent>) {
+        if events.is_empty() {
+            return;
+        }
+
+        let batch_events: Vec<BatchEvent> = events
+            .into_iter()
+            .map(|mut event| {
+                // Merge default properties with event properties
+                // Event properties take precedence over defaults
+                for (key, value) in &self.default_properties {
+                    event.properties.entry(key.clone()).or_insert(value.clone());
+                }
+
+                BatchEvent { event: event.event, properties: event.properties, distinct_id: self.distinct_id.clone() }
+            })
+            .collect();
+
+        let payload = BatchCaptureRequest { api_key: self.config.api_key.clone(), batch: batch_events };
+
+        // Serialize payload to JSON bytes
+        let payload_json = match serde_json::to_vec(&payload) {
+            Ok(json) => json,
+            Err(e) => {
+                error!("Failed to serialize telemetry payload: {}", e);
+                return;
+            }
+        };
+
+        // Generate signature
+        let signature = self.sign_payload(&payload_json);
+        let url = format!("https://{}/batch", self.config.api_host);
+
+        // Send request with signature header
+        match self.client.post(&url).header("X-Request-Signature", signature).header("Content-Type", "application/json").body(payload_json).send().await {
+            Ok(response) => {
+                let status = response.status();
+                if status.is_success() {
+                    debug!("Telemetry batch sent successfully");
+                } else {
+                    let body = response.text().await.unwrap_or_default();
+                    warn!("PostHog returned status {}: {}", status, body);
+                }
+            }
+            Err(e) => {
+                error!("Failed to send telemetry batch: {}", e);
+                if let Some(source) = e.source() {
+                    error!("Caused by: {}", source);
+                }
+            }
+        }
+    }
+
+    /// Get the distinct ID for this client (useful for debugging)
+    pub fn distinct_id(&self) -> &str {
+        &self.distinct_id
+    }
+
+    /// Get the user ID type for this client (useful for debugging)
+    pub fn user_id_type(&self) -> Option<&str> {
+        self.default_properties.get("user_id_type").and_then(|v| v.as_str())
+    }
+}
+
+/// Build the default properties that are attached to every event.
+fn build_default_properties(id_type: UserIdType) -> HashMap<String, serde_json::Value> {
+    use crate::build_info;
+    use serde_json::Value;
+
+    let mut props = HashMap::new();
+
+    let platform = if cfg!(target_arch = "wasm32") {
+        "browser"
+    } else if cfg!(target_os = "windows") {
+        "desktop-windows"
+    } else if cfg!(target_os = "macos") {
+        "desktop-macos"
+    } else if cfg!(target_os = "linux") {
+        "desktop-linux"
+    } else {
+        "desktop-unknown"
+    };
+
+    props.insert("platform".to_string(), Value::String(platform.to_string()));
+    props.insert("build_version".to_string(), Value::String(build_info::VERSION.to_string()));
+    props.insert("build_commit".to_string(), Value::String(build_info::git_commit_short().to_string()));
+    props.insert("user_id_type".to_string(), Value::String(id_type.as_str().to_string()));
+
+    props
+}

crates/borders-core/src/telemetry/mod.rs

@@ -0,0 +1,128 @@
+//! Telemetry module for tracking analytics events.
+//!
+//! This module provides a simple, cross-platform telemetry client that works
+//! on both native (Tauri) and WASM targets. Events are batched and sent to
+//! PostHog via HTTP in a non-blocking manner.
+
+mod client;
+
+mod system_info;
+mod types;
+mod user_id;
+
+pub use client::TelemetryClient;
+pub use system_info::SystemInfo;
+pub use types::{TelemetryConfig, TelemetryEvent};
+pub use user_id::UserIdType;
+
+#[cfg(not(target_arch = "wasm32"))]
+pub use user_id::get_or_create_user_id;
+
+#[cfg(target_arch = "wasm32")]
+pub use user_id::get_or_create_user_id_async;
+
+use once_cell::sync::OnceCell;
+use std::sync::atomic::{AtomicU64, Ordering};
+
+/// Global telemetry client instance.
+static TELEMETRY_CLIENT: OnceCell<TelemetryClient> = OnceCell::new();
+
+/// Session start timestamp in milliseconds since epoch (for calculating session duration).
+static SESSION_START_MS: AtomicU64 = AtomicU64::new(0);
+
+/// Initialize the global telemetry client with the given configuration.
+///
+/// This should be called once at application startup.
+/// On WASM, this is async to load the user ID from IndexedDB.
+pub async fn init(config: TelemetryConfig) {
+    #[cfg(not(target_arch = "wasm32"))]
+    {
+        let client = TelemetryClient::new(config);
+        if TELEMETRY_CLIENT.set(client).is_err() {
+            tracing::warn!("Telemetry client already initialized");
+        }
+    }
+
+    #[cfg(target_arch = "wasm32")]
+    {
+        let (user_id, id_type) = get_or_create_user_id_async().await;
+        let client = TelemetryClient::new_with_user_id(config, user_id, id_type);
+        if TELEMETRY_CLIENT.set(client).is_err() {
+            tracing::warn!("Telemetry client already initialized");
+        }
+    }
+}
+
+/// Get a reference to the global telemetry client.
+///
+/// Returns None if the client hasn't been initialized yet.
+pub fn client() -> Option<&'static TelemetryClient> {
+    TELEMETRY_CLIENT.get()
+}
+
+/// Track a telemetry event using the global client.
+///
+/// This is a convenience function that will do nothing if the client
+/// hasn't been initialized.
+pub async fn track(event: TelemetryEvent) {
+    if let Some(client) = client() {
+        client.track(event).await;
+    }
+}
+
+/// Track a session start event with detailed system information.
+///
+/// Should be called once after telemetry initialization.
+pub async fn track_session_start() {
+    // Record session start time for duration calculation
+    let now_ms = current_time_ms();
+    SESSION_START_MS.store(now_ms, Ordering::Relaxed);
+
+    let system_info = SystemInfo::collect();
+    let mut event = TelemetryEvent::new("session_start");
+
+    for (key, value) in system_info.to_properties() {
+        event.properties.insert(key, value);
+    }
+
+    #[cfg(target_arch = "wasm32")]
+    {
+        let (browser_name, browser_version) = system_info::get_browser_info();
+        event.properties.insert("browser_name".to_string(), serde_json::Value::String(browser_name));
+        event.properties.insert("browser_version".to_string(), serde_json::Value::String(browser_version));
+    }
+
+    track(event).await;
+}
+
+/// Track a session end event with session duration.
+///
+/// Should be called when the application is closing.
+pub async fn track_session_end() {
+    let start_ms = SESSION_START_MS.load(Ordering::Relaxed);
+    if start_ms == 0 {
+        tracing::warn!("Session end tracked but no session start found");
+        return;
+    }
+
+    let now_ms = current_time_ms();
+    let duration_ms = now_ms.saturating_sub(start_ms);
+    let duration_secs = duration_ms / 1000;
+
+    let event = TelemetryEvent::new("session_end").with_property("session_duration_ms", duration_ms).with_property("session_duration_secs", duration_secs);
+
+    track(event).await;
+}
+
+/// Get current time in milliseconds since Unix epoch.
+fn current_time_ms() -> u64 {
+    #[cfg(not(target_arch = "wasm32"))]
+    {
+        std::time::SystemTime::now().duration_since(std::time::UNIX_EPOCH).unwrap().as_millis() as u64
+    }
+
+    #[cfg(target_arch = "wasm32")]
+    {
+        (js_sys::Date::now()) as u64
+    }
+}

crates/borders-core/src/telemetry/system_info.rs

@@ -0,0 +1,148 @@
+//! System information collection for analytics.
+//!
+//! Collects platform-specific system information for telemetry purposes.
+
+use serde_json::Value;
+use std::collections::HashMap;
+
+/// Detailed system information collected once at session start.
+#[derive(Debug, Clone)]
+pub struct SystemInfo {
+    pub os_name: String,
+    pub os_version: String,
+    pub arch: String,
+    pub cpu_brand: Option<String>,
+    pub cpu_cores: Option<usize>,
+    pub total_memory_mb: Option<u64>,
+}
+
+impl SystemInfo {
+    /// Collect system information for the current platform.
+    pub fn collect() -> Self {
+        #[cfg(not(target_arch = "wasm32"))]
+        {
+            Self::collect_native()
+        }
+
+        #[cfg(target_arch = "wasm32")]
+        {
+            Self::collect_wasm()
+        }
+    }
+
+    /// Convert system info to a HashMap for inclusion in telemetry events.
+    pub fn to_properties(&self) -> HashMap<String, Value> {
+        let mut props = HashMap::new();
+        props.insert("os_name".to_string(), Value::String(self.os_name.clone()));
+        props.insert("os_version".to_string(), Value::String(self.os_version.clone()));
+        props.insert("arch".to_string(), Value::String(self.arch.clone()));
+
+        if let Some(brand) = &self.cpu_brand {
+            props.insert("cpu_brand".to_string(), Value::String(brand.clone()));
+        }
+        if let Some(cores) = self.cpu_cores {
+            props.insert("cpu_cores".to_string(), Value::Number(cores.into()));
+        }
+        if let Some(mem) = self.total_memory_mb {
+            props.insert("total_memory_mb".to_string(), Value::Number(mem.into()));
+        }
+
+        props
+    }
+
+    #[cfg(not(target_arch = "wasm32"))]
+    fn collect_native() -> Self {
+        use sysinfo::System;
+
+        let mut sys = System::new_all();
+        sys.refresh_all();
+
+        let os_name = System::name().unwrap_or_else(|| "Unknown".to_string());
+        let os_version = System::os_version().unwrap_or_else(|| "Unknown".to_string());
+        let arch = std::env::consts::ARCH.to_string();
+
+        let cpu_brand = sys.cpus().first().map(|cpu| cpu.brand().to_string());
+        let cpu_cores = sys.cpus().len();
+        let total_memory_mb = sys.total_memory() / 1024 / 1024;
+
+        Self { os_name, os_version, arch, cpu_brand, cpu_cores: Some(cpu_cores), total_memory_mb: Some(total_memory_mb) }
+    }
+
+    #[cfg(target_arch = "wasm32")]
+    fn collect_wasm() -> Self {
+        use wasm_bindgen::JsValue;
+
+        // In web workers, use the global scope instead of window
+        let global = js_sys::global();
+        let navigator = js_sys::Reflect::get(&global, &JsValue::from_str("navigator")).expect("navigator should be available");
+
+        // Call methods using Reflect to work with both Navigator and WorkerNavigator
+        let user_agent = js_sys::Reflect::get(&navigator, &JsValue::from_str("userAgent")).ok().and_then(|v| v.as_string()).unwrap_or_default();
+        let platform = js_sys::Reflect::get(&navigator, &JsValue::from_str("platform")).ok().and_then(|v| v.as_string()).unwrap_or_default();
+
+        let (os_name, os_version) = parse_user_agent(&user_agent);
+        let arch = platform;
+
+        let cpu_cores = js_sys::Reflect::get(&navigator, &JsValue::from_str("hardwareConcurrency")).ok().and_then(|v| v.as_f64()).and_then(|f| if f > 0.0 { Some(f as usize) } else { None });
+
+        let device_memory = js_sys::Reflect::get(&navigator, &JsValue::from_str("deviceMemory")).ok().and_then(|v| v.as_f64()).map(|gb| (gb * 1024.0) as u64);
+
+        Self { os_name, os_version, arch, cpu_brand: None, cpu_cores, total_memory_mb: device_memory }
+    }
+}
+
+/// Parse user agent string to extract OS name and version.
+#[cfg(target_arch = "wasm32")]
+fn parse_user_agent(ua: &str) -> (String, String) {
+    if ua.contains("Windows NT 10.0") {
+        ("Windows".to_string(), "10/11".to_string())
+    } else if ua.contains("Windows NT 6.3") {
+        ("Windows".to_string(), "8.1".to_string())
+    } else if ua.contains("Windows NT 6.2") {
+        ("Windows".to_string(), "8".to_string())
+    } else if ua.contains("Windows NT 6.1") {
+        ("Windows".to_string(), "7".to_string())
+    } else if ua.contains("Mac OS X") {
+        let version = ua.split("Mac OS X ").nth(1).and_then(|s| s.split(')').next()).unwrap_or("Unknown");
+        ("macOS".to_string(), version.replace('_', "."))
+    } else if ua.contains("Android") {
+        let version = ua.split("Android ").nth(1).and_then(|s| s.split(';').next()).unwrap_or("Unknown");
+        ("Android".to_string(), version.to_string())
+    } else if ua.contains("Linux") {
+        ("Linux".to_string(), "Unknown".to_string())
+    } else if ua.contains("iOS") || ua.contains("iPhone") || ua.contains("iPad") {
+        let version = ua.split("OS ").nth(1).and_then(|s| s.split(' ').next()).unwrap_or("Unknown");
+        ("iOS".to_string(), version.replace('_', "."))
+    } else {
+        ("Unknown".to_string(), "Unknown".to_string())
+    }
+}
+
+/// Get browser name and version from user agent.
+#[cfg(target_arch = "wasm32")]
+pub fn get_browser_info() -> (String, String) {
+    use wasm_bindgen::JsValue;
+
+    // In web workers, use the global scope instead of window
+    let global = js_sys::global();
+    let navigator = js_sys::Reflect::get(&global, &JsValue::from_str("navigator")).expect("navigator should be available");
+
+    // Call methods using Reflect to work with both Navigator and WorkerNavigator
+    let ua = js_sys::Reflect::get(&navigator, &JsValue::from_str("userAgent")).ok().and_then(|v| v.as_string()).unwrap_or_default();
+
+    if ua.contains("Edg/") {
+        let version = ua.split("Edg/").nth(1).and_then(|s| s.split(' ').next()).unwrap_or("Unknown");
+        ("Edge".to_string(), version.to_string())
+    } else if ua.contains("Chrome/") {
+        let version = ua.split("Chrome/").nth(1).and_then(|s| s.split(' ').next()).unwrap_or("Unknown");
+        ("Chrome".to_string(), version.to_string())
+    } else if ua.contains("Firefox/") {
+        let version = ua.split("Firefox/").nth(1).and_then(|s| s.split(' ').next()).unwrap_or("Unknown");
+        ("Firefox".to_string(), version.to_string())
+    } else if ua.contains("Safari/") && !ua.contains("Chrome") {
+        let version = ua.split("Version/").nth(1).and_then(|s| s.split(' ').next()).unwrap_or("Unknown");
+        ("Safari".to_string(), version.to_string())
+    } else {
+        ("Unknown".to_string(), "Unknown".to_string())
+    }
+}

crates/borders-core/src/telemetry/types.rs

@@ -0,0 +1,77 @@
+use serde::{Deserialize, Serialize};
+use std::collections::HashMap;
+
+/// Represents a telemetry event to be sent to PostHog.
+#[derive(Debug, Clone, Serialize, Deserialize)]
+pub struct TelemetryEvent {
+    /// Unique event identifier (e.g., "app_started", "game_ended")
+    pub event: String,
+
+    /// Properties associated with this event
+    #[serde(skip_serializing_if = "HashMap::is_empty")]
+    pub properties: HashMap<String, serde_json::Value>,
+}
+
+impl TelemetryEvent {
+    pub fn new(event: impl Into<String>) -> Self {
+        Self { event: event.into(), properties: HashMap::new() }
+    }
+
+    pub fn with_property(mut self, key: impl Into<String>, value: impl Into<serde_json::Value>) -> Self {
+        self.properties.insert(key.into(), value.into());
+        self
+    }
+}
+
+/// Configuration for the telemetry client.
+#[derive(Debug, Clone)]
+pub struct TelemetryConfig {
+    /// PostHog API key
+    pub api_key: String,
+
+    /// API host (e.g., "observe.borders.xevion.dev")
+    pub api_host: String,
+
+    /// Batch size - send events when this many are queued
+    pub batch_size: usize,
+
+    /// Flush interval in seconds
+    pub flush_interval_secs: u64,
+
+    /// HMAC signing key for request integrity verification
+    pub signing_key: String,
+}
+
+impl Default for TelemetryConfig {
+    fn default() -> Self {
+        // In development: send often with small batch size for fast feedback
+        // In production: batch events but flush periodically to avoid losing data
+        #[cfg(debug_assertions)]
+        let (batch_size, flush_interval_secs) = (2, 5);
+        #[cfg(not(debug_assertions))]
+        let (batch_size, flush_interval_secs) = (10, 45);
+
+        Self {
+            api_key: "phc_VmL3M9Sn9hBCpNRExnKLWOZqlYO5SXSUkAAwl3gXJek".to_string(),
+            api_host: "observe.borders.xevion.dev".to_string(),
+            batch_size,
+            flush_interval_secs,
+            // HMAC-SHA256 signing key for request integrity
+            signing_key: "borders_telemetry_hmac_key_v1_2025".to_string(),
+        }
+    }
+}
+
+/// PostHog batch capture request payload
+#[derive(Debug, Serialize)]
+pub(crate) struct BatchCaptureRequest {
+    pub api_key: String,
+    pub batch: Vec<BatchEvent>,
+}
+
+#[derive(Debug, Serialize)]
+pub(crate) struct BatchEvent {
+    pub event: String,
+    pub properties: HashMap<String, serde_json::Value>,
+    pub distinct_id: String,
+}

crates/borders-core/src/telemetry/user_id.rs

@@ -0,0 +1,268 @@
+use tracing::debug;
+use uuid::Uuid;
+
+#[cfg(not(target_arch = "wasm32"))]
+use tracing::warn;
+
+/// Type of user ID that was generated or loaded.
+#[derive(Debug, Clone, Copy, PartialEq, Eq)]
+pub enum UserIdType {
+    /// ID was loaded from storage (existing user)
+    Existing,
+    /// ID was generated from hardware components
+    Hardware,
+    /// ID was newly generated random UUID
+    New,
+}
+
+impl UserIdType {
+    pub fn as_str(&self) -> &'static str {
+        match self {
+            UserIdType::Existing => "existing",
+            UserIdType::Hardware => "hardware",
+            UserIdType::New => "new",
+        }
+    }
+}
+
+/// Get or create a persistent user ID (sync version for native platforms).
+///
+/// This function attempts to identify the user through multiple strategies:
+/// 1. Stored UUID (persisted across runs, most reliable)
+/// 2. Hardware-based ID (hashed for privacy, then stored for future use)
+/// 3. Generate new UUID (if nothing exists)
+///
+/// Returns a tuple of (user_id, id_type).
+#[cfg(not(target_arch = "wasm32"))]
+pub fn get_or_create_user_id() -> (String, UserIdType) {
+    // Try to load stored ID first (most reliable)
+    if let Some(stored_id) = load_stored_id() {
+        debug!("Using stored user ID");
+        return (stored_id, UserIdType::Existing);
+    }
+
+    // Try hardware-based ID
+    if let Some(hw_id) = get_hardware_id() {
+        debug!("Generated hardware-based user ID");
+        // Store it for future reliability
+        if let Err(e) = store_user_id(&hw_id) {
+            warn!("Failed to store hardware-based user ID: {}", e);
+        }
+        return (hw_id, UserIdType::Hardware);
+    }
+
+    // Generate and store new ID
+    let new_id = Uuid::new_v4().to_string();
+    debug!("Generated new user ID");
+
+    if let Err(e) = store_user_id(&new_id) {
+        warn!("Failed to store new user ID: {}", e);
+    }
+
+    (new_id, UserIdType::New)
+}
+
+/// Get or create a persistent user ID (async version for WASM).
+///
+/// This function attempts to identify the user through multiple strategies:
+/// 1. Stored UUID in localStorage (via main thread, persisted across runs)
+/// 2. Generate new UUID (if nothing exists)
+///
+/// Returns a tuple of (user_id, id_type).
+#[cfg(target_arch = "wasm32")]
+pub async fn get_or_create_user_id_async() -> (String, UserIdType) {
+    // Try to load from localStorage via main thread
+    if let Some(stored_id) = load_from_localstorage().await {
+        debug!("Loaded user ID from localStorage");
+        return (stored_id, UserIdType::Existing);
+    }
+
+    // Generate and store new ID
+    let new_id = Uuid::new_v4().to_string();
+    debug!("Generated new user ID");
+
+    // Try to store it (fire and forget)
+    store_user_id(&new_id).ok();
+
+    (new_id, UserIdType::New)
+}
+
+/// Attempt to get a hardware-based identifier.
+///
+/// Uses machineid-rs to build a stable ID from hardware components.
+/// The ID is hashed with SHA256 for privacy.
+///
+/// Only available on native platforms (not WASM).
+#[cfg(not(target_arch = "wasm32"))]
+fn get_hardware_id() -> Option<String> {
+    use machineid_rs::{Encryption, HWIDComponent, IdBuilder};
+
+    match IdBuilder::new(Encryption::SHA256).add_component(HWIDComponent::SystemID).add_component(HWIDComponent::CPUCores).build("iron-borders") {
+        Ok(id) => {
+            debug!("Successfully generated hardware ID");
+            Some(id)
+        }
+        Err(e) => {
+            warn!("Failed to generate hardware ID: {}", e);
+            None
+        }
+    }
+}
+
+/// Hardware IDs are not available on WASM.
+#[cfg(target_arch = "wasm32")]
+#[allow(dead_code)]
+fn get_hardware_id() -> Option<String> {
+    None
+}
+
+/// Load a previously stored user ID from platform-specific storage.
+#[cfg(not(target_arch = "wasm32"))]
+fn load_stored_id() -> Option<String> {
+    #[cfg(windows)]
+    {
+        load_from_registry()
+    }
+
+    #[cfg(not(windows))]
+    {
+        load_from_file()
+    }
+}
+
+/// Store a user ID to platform-specific storage.
+#[cfg(not(target_arch = "wasm32"))]
+fn store_user_id(id: &str) -> Result<(), String> {
+    #[cfg(windows)]
+    {
+        store_to_registry(id)
+    }
+
+    #[cfg(not(windows))]
+    {
+        store_to_file(id)
+    }
+}
+
+#[cfg(target_arch = "wasm32")]
+fn store_user_id(id: &str) -> Result<(), String> {
+    use wasm_bindgen::JsValue;
+    use web_sys::BroadcastChannel;
+
+    let channel = BroadcastChannel::new("user_id_storage").ok().ok_or("Failed to create channel")?;
+    let msg = format!(r#"{{"action":"save","id":"{}"}}"#, id);
+    channel.post_message(&JsValue::from_str(&msg)).ok().ok_or("Failed to post")?;
+    Ok(())
+}
+
+#[cfg(windows)]
+fn load_from_registry() -> Option<String> {
+    use winreg::RegKey;
+    use winreg::enums::*;
+
+    let hkcu = RegKey::predef(HKEY_CURRENT_USER);
+
+    match hkcu.open_subkey("Software\\Iron Borders\\ClientCache") {
+        Ok(key) => match key.get_value::<String, _>("sid") {
+            Ok(id) => {
+                debug!("Loaded user ID from registry");
+                Some(id)
+            }
+            Err(_) => None,
+        },
+        Err(_) => None,
+    }
+}
+
+#[cfg(windows)]
+fn store_to_registry(id: &str) -> Result<(), String> {
+    use winreg::RegKey;
+    use winreg::enums::*;
+
+    let hkcu = RegKey::predef(HKEY_CURRENT_USER);
+
+    let (key, _) = hkcu.create_subkey("Software\\Iron Borders\\ClientCache").map_err(|e| format!("Failed to create registry key: {}", e))?;
+
+    key.set_value("sid", &id).map_err(|e| format!("Failed to set registry value: {}", e))?;
+
+    debug!("Stored user ID to registry");
+    Ok(())
+}
+
+#[cfg(all(not(target_arch = "wasm32"), not(windows)))]
+fn load_from_file() -> Option<String> {
+    use directories::ProjectDirs;
+    use std::fs;
+
+    let proj_dirs = ProjectDirs::from("", "", "iron-borders")?;
+    let data_dir = proj_dirs.data_dir();
+    let file_path = data_dir.join("client.dat");
+
+    match fs::read_to_string(&file_path) {
+        Ok(id) => {
+            debug!("Loaded user ID from file: {:?}", file_path);
+            Some(id.trim().to_string())
+        }
+        Err(_) => None,
+    }
+}
+
+#[cfg(all(not(target_arch = "wasm32"), not(windows)))]
+fn store_to_file(id: &str) -> Result<(), String> {
+    use directories::ProjectDirs;
+    use std::fs;
+
+    let proj_dirs = ProjectDirs::from("", "", "iron-borders").ok_or("Failed to get project directories")?;
+
+    let data_dir = proj_dirs.data_dir();
+
+    // Create directory if it doesn't exist
+    fs::create_dir_all(data_dir).map_err(|e| format!("Failed to create data directory: {}", e))?;
+
+    let file_path = data_dir.join("client.dat");
+
+    fs::write(&file_path, id).map_err(|e| format!("Failed to write user ID file: {}", e))?;
+
+    debug!("Stored user ID to file: {:?}", file_path);
+    Ok(())
+}
+
+#[cfg(target_arch = "wasm32")]
+async fn load_from_localstorage() -> Option<String> {
+    use gloo_timers::future::TimeoutFuture;
+    use std::sync::Arc;
+    use std::sync::Mutex;
+    use wasm_bindgen::JsCast;
+    use wasm_bindgen::prelude::*;
+    use web_sys::{BroadcastChannel, MessageEvent};
+
+    let channel = BroadcastChannel::new("user_id_storage").ok()?;
+    let result = Arc::new(Mutex::new(None));
+    let result_clone = result.clone();
+
+    let callback = Closure::wrap(Box::new(move |event: MessageEvent| {
+        if let Some(data) = event.data().as_string()
+            && let Ok(parsed) = js_sys::JSON::parse(&data)
+            && let Some(obj) = parsed.dyn_ref::<js_sys::Object>()
+            && let Ok(action) = js_sys::Reflect::get(obj, &JsValue::from_str("action"))
+            && action.as_string().as_deref() == Some("load_response")
+            && let Ok(id_val) = js_sys::Reflect::get(obj, &JsValue::from_str("id"))
+            && let Some(id) = id_val.as_string()
+        {
+            *result_clone.lock().unwrap() = Some(id);
+        }
+    }) as Box<dyn FnMut(_)>);
+
+    channel.set_onmessage(Some(callback.as_ref().unchecked_ref()));
+
+    // Send load request
+    let msg = r#"{"action":"load"}"#;
+    channel.post_message(&JsValue::from_str(msg)).ok()?;
+
+    // Wait up to 100ms for response
+    TimeoutFuture::new(100).await;
+
+    callback.forget();
+
+    result.lock().unwrap().clone()
+}

crates/borders-core/src/time.rs

@@ -0,0 +1,58 @@
+/// Simple time tracking resource for ECS
+use bevy_ecs::prelude::Resource;
+use std::time::Duration;
+
+#[derive(Debug, Clone, Resource)]
+pub struct Time {
+    delta: Duration,
+    elapsed: Duration,
+}
+
+impl Time {
+    pub fn new() -> Self {
+        Self { delta: Duration::ZERO, elapsed: Duration::ZERO }
+    }
+
+    pub fn update(&mut self, delta: Duration) {
+        self.delta = delta;
+        self.elapsed += delta;
+    }
+
+    pub fn delta(&self) -> Duration {
+        self.delta
+    }
+
+    pub fn delta_secs(&self) -> f32 {
+        self.delta.as_secs_f32()
+    }
+
+    pub fn elapsed(&self) -> Duration {
+        self.elapsed
+    }
+
+    pub fn elapsed_secs(&self) -> f32 {
+        self.elapsed.as_secs_f32()
+    }
+}
+
+impl Default for Time {
+    fn default() -> Self {
+        Self::new()
+    }
+}
+
+/// Fixed timestep time resource
+#[derive(Debug, Clone, Resource)]
+pub struct FixedTime {
+    timestep: Duration,
+}
+
+impl FixedTime {
+    pub fn from_seconds(seconds: f64) -> Self {
+        Self { timestep: Duration::from_secs_f64(seconds) }
+    }
+
+    pub fn timestep(&self) -> Duration {
+        self.timestep
+    }
+}

crates/borders-core/src/ui/input.rs

@@ -0,0 +1,350 @@
+//! Platform-agnostic input handling for the game
+//!
+//! This module provides input types and utilities that work across
+//! all platforms (WASM, Tauri) without depending on Bevy's input system.
+
+use bevy_ecs::prelude::Resource;
+
+/// Mouse button identifier
+#[derive(Debug, Clone, Copy, PartialEq, Eq, Hash)]
+pub enum MouseButton {
+    Left = 0,
+    Middle = 1,
+    Right = 2,
+    Back = 3,
+    Forward = 4,
+}
+
+impl MouseButton {
+    pub fn from_u8(button: u8) -> Option<Self> {
+        match button {
+            0 => Some(Self::Left),
+            1 => Some(Self::Middle),
+            2 => Some(Self::Right),
+            3 => Some(Self::Back),
+            4 => Some(Self::Forward),
+            _ => None,
+        }
+    }
+}
+
+/// Keyboard key codes (subset we actually use)
+#[derive(Debug, Clone, Copy, PartialEq, Eq, Hash)]
+pub enum KeyCode {
+    KeyW,
+    KeyA,
+    KeyS,
+    KeyD,
+    KeyC,
+    Digit1,
+    Digit2,
+    Space,
+    Escape,
+}
+
+impl KeyCode {
+    pub fn from_string(key: &str) -> Option<Self> {
+        match key {
+            "KeyW" | "w" => Some(Self::KeyW),
+            "KeyA" | "a" => Some(Self::KeyA),
+            "KeyS" | "s" => Some(Self::KeyS),
+            "KeyD" | "d" => Some(Self::KeyD),
+            "KeyC" | "c" => Some(Self::KeyC),
+            "Digit1" | "1" => Some(Self::Digit1),
+            "Digit2" | "2" => Some(Self::Digit2),
+            "Space" | " " => Some(Self::Space),
+            "Escape" => Some(Self::Escape),
+            _ => None,
+        }
+    }
+}
+
+/// Button state (pressed or released)
+#[derive(Debug, Clone, Copy, PartialEq, Eq)]
+pub enum ButtonState {
+    Pressed,
+    Released,
+}
+
+/// World coordinates (in game units)
+#[derive(Debug, Clone, Copy)]
+pub struct WorldPos {
+    pub x: f32,
+    pub y: f32,
+}
+
+/// Screen coordinates (in pixels)
+#[derive(Debug, Clone, Copy)]
+pub struct ScreenPos {
+    pub x: f32,
+    pub y: f32,
+}
+
+/// Tile coordinates on the map
+#[derive(Debug, Clone, Copy, PartialEq, Eq)]
+pub struct TileCoord {
+    pub x: u32,
+    pub y: u32,
+}
+
+impl TileCoord {
+    /// Convert to linear tile index
+    pub fn to_index(&self, map_width: u32) -> usize {
+        (self.y * map_width + self.x) as usize
+    }
+
+    /// Create from linear tile index
+    pub fn from_index(index: usize, map_width: u32) -> Self {
+        Self { x: (index as u32) % map_width, y: (index as u32) / map_width }
+    }
+}
+
+/// Camera state for coordinate conversions
+#[derive(Debug, Clone, Copy)]
+pub struct CameraState {
+    /// Camera position in world coordinates
+    pub x: f32,
+    pub y: f32,
+    /// Camera zoom level (1.0 = normal)
+    pub zoom: f32,
+    /// Viewport width in pixels
+    pub viewport_width: f32,
+    /// Viewport height in pixels
+    pub viewport_height: f32,
+}
+
+/// Input event from the frontend
+#[derive(Debug, Clone)]
+pub enum InputEvent {
+    MouseButton { button: MouseButton, state: ButtonState, world_pos: Option<WorldPos>, tile: Option<TileCoord> },
+    MouseMove { world_pos: WorldPos, screen_pos: ScreenPos, tile: Option<TileCoord> },
+    MouseWheel { delta_x: f32, delta_y: f32 },
+    KeyPress { key: KeyCode, state: ButtonState },
+}
+
+#[derive(Debug, Default, Resource)]
+pub struct InputState {
+    // Mouse state
+    mouse_buttons: Vec<(MouseButton, ButtonState)>,
+    cursor_world_pos: Option<WorldPos>,
+    cursor_tile: Option<TileCoord>,
+    mouse_wheel_delta: (f32, f32),
+
+    // Keyboard state
+    keys_pressed: Vec<KeyCode>,
+    keys_just_pressed: Vec<KeyCode>,
+    keys_just_released: Vec<KeyCode>,
+
+    // Track if camera was interacted with (for click filtering)
+    camera_interaction: bool,
+}
+
+impl InputState {
+    pub fn new() -> Self {
+        Self::default()
+    }
+
+    /// Clear per-frame data (call at start of frame)
+    pub fn clear_frame_data(&mut self) {
+        self.mouse_buttons.clear();
+        self.keys_just_pressed.clear();
+        self.keys_just_released.clear();
+        self.mouse_wheel_delta = (0.0, 0.0);
+        self.camera_interaction = false;
+    }
+
+    /// Process an input event
+    pub fn handle_event(&mut self, event: InputEvent) {
+        match event {
+            InputEvent::MouseButton { button, state, world_pos, tile } => {
+                self.mouse_buttons.push((button, state));
+                if world_pos.is_some() {
+                    self.cursor_world_pos = world_pos;
+                }
+                if tile.is_some() {
+                    self.cursor_tile = tile;
+                }
+            }
+            InputEvent::MouseMove { world_pos, tile, .. } => {
+                self.cursor_world_pos = Some(world_pos);
+                self.cursor_tile = tile;
+            }
+            InputEvent::MouseWheel { delta_x, delta_y } => {
+                self.mouse_wheel_delta.0 += delta_x;
+                self.mouse_wheel_delta.1 += delta_y;
+                // Mouse wheel = camera interaction
+                if delta_x.abs() > 0.0 || delta_y.abs() > 0.0 {
+                    self.camera_interaction = true;
+                }
+            }
+            InputEvent::KeyPress { key, state } => match state {
+                ButtonState::Pressed => {
+                    if !self.keys_pressed.contains(&key) {
+                        self.keys_pressed.push(key);
+                        self.keys_just_pressed.push(key);
+                    }
+                }
+                ButtonState::Released => {
+                    self.keys_pressed.retain(|&k| k != key);
+                    self.keys_just_released.push(key);
+                }
+            },
+        }
+    }
+
+    /// Check if a mouse button was just pressed this frame
+    pub fn mouse_just_pressed(&self, button: MouseButton) -> bool {
+        self.mouse_buttons.iter().any(|&(b, s)| b == button && s == ButtonState::Pressed)
+    }
+
+    /// Check if a mouse button was just released this frame
+    pub fn mouse_just_released(&self, button: MouseButton) -> bool {
+        self.mouse_buttons.iter().any(|&(b, s)| b == button && s == ButtonState::Released)
+    }
+
+    /// Check if a key is currently pressed
+    pub fn key_pressed(&self, key: KeyCode) -> bool {
+        self.keys_pressed.contains(&key)
+    }
+
+    /// Check if a key was just pressed this frame
+    pub fn key_just_pressed(&self, key: KeyCode) -> bool {
+        self.keys_just_pressed.contains(&key)
+    }
+
+    /// Check if a key was just released this frame
+    pub fn key_just_released(&self, key: KeyCode) -> bool {
+        self.keys_just_released.contains(&key)
+    }
+
+    /// Get current cursor position in world coordinates
+    pub fn cursor_world_pos(&self) -> Option<WorldPos> {
+        self.cursor_world_pos
+    }
+
+    /// Get current tile under cursor
+    pub fn cursor_tile(&self) -> Option<TileCoord> {
+        self.cursor_tile
+    }
+
+    /// Get mouse wheel delta for this frame
+    pub fn mouse_wheel_delta(&self) -> (f32, f32) {
+        self.mouse_wheel_delta
+    }
+
+    /// Check if camera was interacted with (for filtering clicks)
+    pub fn had_camera_interaction(&self) -> bool {
+        self.camera_interaction
+    }
+
+    /// Mark that camera was interacted with
+    pub fn set_camera_interaction(&mut self) {
+        self.camera_interaction = true;
+    }
+}
+
+/// Coordinate conversion utilities
+pub mod coords {
+    use super::*;
+
+    /// Convert screen position to world position
+    pub fn screen_to_world(screen: ScreenPos, camera: &CameraState) -> WorldPos {
+        // Adjust for camera position and zoom
+        let world_x = (screen.x - camera.viewport_width / 2.0) / camera.zoom + camera.x;
+        let world_y = (screen.y - camera.viewport_height / 2.0) / camera.zoom + camera.y;
+        WorldPos { x: world_x, y: world_y }
+    }
+
+    /// Convert world position to screen position
+    pub fn world_to_screen(world: WorldPos, camera: &CameraState) -> ScreenPos {
+        let screen_x = (world.x - camera.x) * camera.zoom + camera.viewport_width / 2.0;
+        let screen_y = (world.y - camera.y) * camera.zoom + camera.viewport_height / 2.0;
+        ScreenPos { x: screen_x, y: screen_y }
+    }
+
+    /// Convert world position to tile coordinates
+    pub fn world_to_tile(world: WorldPos, map_width: u32, map_height: u32, pixel_scale: f32) -> Option<TileCoord> {
+        // Adjust for centered map
+        let half_width = (map_width as f32 * pixel_scale) / 2.0;
+        let half_height = (map_height as f32 * pixel_scale) / 2.0;
+
+        let adjusted_x = world.x + half_width;
+        let adjusted_y = world.y + half_height;
+
+        let tile_x = (adjusted_x / pixel_scale) as i32;
+        let tile_y = (adjusted_y / pixel_scale) as i32;
+
+        if tile_x >= 0 && tile_x < map_width as i32 && tile_y >= 0 && tile_y < map_height as i32 { Some(TileCoord { x: tile_x as u32, y: tile_y as u32 }) } else { None }
+    }
+
+    /// Convert tile coordinates to world position (center of tile)
+    pub fn tile_to_world(tile: TileCoord, map_width: u32, map_height: u32, pixel_scale: f32) -> WorldPos {
+        let half_width = (map_width as f32 * pixel_scale) / 2.0;
+        let half_height = (map_height as f32 * pixel_scale) / 2.0;
+
+        WorldPos { x: (tile.x as f32 + 0.5) * pixel_scale - half_width, y: (tile.y as f32 + 0.5) * pixel_scale - half_height }
+    }
+
+    /// Convert tile index to world position
+    pub fn tile_index_to_world(index: usize, map_width: u32, map_height: u32, pixel_scale: f32) -> WorldPos {
+        let tile = TileCoord::from_index(index, map_width);
+        tile_to_world(tile, map_width, map_height, pixel_scale)
+    }
+
+    /// Convert screen position directly to tile (combines screen_to_world and world_to_tile)
+    pub fn screen_to_tile(screen: ScreenPos, camera: &CameraState, map_width: u32, map_height: u32, pixel_scale: f32) -> Option<TileCoord> {
+        let world = screen_to_world(screen, camera);
+        world_to_tile(world, map_width, map_height, pixel_scale)
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn test_tile_coord_conversion() {
+        let tile = TileCoord { x: 5, y: 3 };
+        let index = tile.to_index(10);
+        assert_eq!(index, 35); // 3 * 10 + 5
+
+        let tile2 = TileCoord::from_index(35, 10);
+        assert_eq!(tile2.x, 5);
+        assert_eq!(tile2.y, 3);
+    }
+
+    #[test]
+    fn test_input_state() {
+        let mut state = InputState::new();
+
+        // Test key press
+        state.handle_event(InputEvent::KeyPress { key: KeyCode::KeyC, state: ButtonState::Pressed });
+        assert!(state.key_just_pressed(KeyCode::KeyC));
+        assert!(state.key_pressed(KeyCode::KeyC));
+
+        // Clear frame data
+        state.clear_frame_data();
+        assert!(!state.key_just_pressed(KeyCode::KeyC));
+        assert!(state.key_pressed(KeyCode::KeyC)); // Still pressed
+
+        // Release key
+        state.handle_event(InputEvent::KeyPress { key: KeyCode::KeyC, state: ButtonState::Released });
+        assert!(state.key_just_released(KeyCode::KeyC));
+        assert!(!state.key_pressed(KeyCode::KeyC));
+    }
+
+    #[test]
+    fn test_coordinate_conversion() {
+        let camera = CameraState { x: 100.0, y: 100.0, zoom: 2.0, viewport_width: 800.0, viewport_height: 600.0 };
+
+        let screen = ScreenPos { x: 400.0, y: 300.0 };
+        let world = coords::screen_to_world(screen, &camera);
+        assert_eq!(world.x, 100.0); // Center of screen = camera position
+        assert_eq!(world.y, 100.0);
+
+        // Test round trip
+        let screen2 = coords::world_to_screen(world, &camera);
+        assert!((screen2.x - screen.x).abs() < 0.001);
+        assert!((screen2.y - screen.y).abs() < 0.001);
+    }
+}

crates/borders-core/src/ui/leaderboard.rs

@@ -0,0 +1,160 @@
+//! Shared leaderboard data structures and utilities
+//!
+//! This module contains types and systems for managing leaderboard data
+//! that are shared between desktop and WASM builds.
+
+use bevy_ecs::prelude::*;
+
+use crate::game::GameInstance;
+use crate::networking::GameView;
+
+#[cfg(not(target_arch = "wasm32"))]
+use std::time::Instant;
+
+#[cfg(target_arch = "wasm32")]
+use web_time::Instant;
+
+// Re-export UI types from protocol for convenience
+pub use crate::ui::protocol::{AttackEntry, AttacksUpdatePayload, BackendMessage, LeaderboardEntry, LeaderboardSnapshot};
+
+/// Convert RGBA color to hex string (without alpha)
+pub fn rgba_to_hex(color: [f32; 4]) -> String {
+    let r = (color[0] * 255.0) as u8;
+    let g = (color[1] * 255.0) as u8;
+    let b = (color[2] * 255.0) as u8;
+    format!("{:02X}{:02X}{:02X}", r, g, b)
+}
+
+/// Resource to track last emitted leaderboard state for deduplication
+#[derive(Resource, Default, Debug)]
+pub struct LastLeaderboardDigest {
+    pub entries: Vec<(u16, String, u32, u32)>, // (id, name, tile_count, troops)
+    pub turn: u64,
+}
+
+/// Resource to track last emitted attacks state for deduplication
+#[derive(Resource, Default, Debug)]
+pub struct LastAttacksDigest {
+    pub entries: Vec<(usize, Option<usize>, u32, u64, bool)>, // (attacker_id, target_id, troops, start_turn, is_outgoing)
+    pub turn: u64,
+}
+
+/// Resource to throttle leaderboard snapshot emissions
+#[derive(Resource, Debug)]
+pub struct LeaderboardThrottle {
+    last_emission: Option<Instant>,
+    throttle_duration: core::time::Duration,
+}
+
+impl Default for LeaderboardThrottle {
+    fn default() -> Self {
+        Self {
+            last_emission: None,
+            throttle_duration: core::time::Duration::from_millis(1250), // 1.25 seconds
+        }
+    }
+}
+
+/// Build a complete leaderboard snapshot from current game state
+/// Returns None if nothing has changed since last_digest
+pub fn build_leaderboard_snapshot(game_view: &GameView, game: &GameInstance, last_digest: &mut LastLeaderboardDigest) -> Option<LeaderboardSnapshot> {
+    // Use cached total_land_tiles from GameView (performance optimization)
+    let total_land_tiles = game_view.total_land_tiles;
+
+    // Get player manager to look up names/colors
+    let players_by_id: std::collections::HashMap<usize, &crate::game::Player> = game.player_manager.get_players().iter().map(|p| (p.id, p)).collect();
+
+    // Build current digest for comparison (includes names now)
+    let current_entries: Vec<(u16, String, u32, u32)> = game_view
+        .players
+        .iter()
+        .map(|p| {
+            let player = players_by_id.get(&(p.id as usize));
+            let name = player.map(|pl| if pl.name.is_empty() { if pl.id == game.player_manager.client_player_id { "Player".to_string() } else { format!("Nation {}", pl.id) } } else { pl.name.clone() }).unwrap_or_else(|| format!("Nation {}", p.id));
+            (p.id, name, p.tile_count, p.troops)
+        })
+        .collect();
+
+    // Check if anything has changed (stats OR names)
+    if current_entries == last_digest.entries && game.turn_number == last_digest.turn {
+        return None; // No changes
+    }
+
+    // Update digest
+    last_digest.entries = current_entries;
+    last_digest.turn = game.turn_number;
+
+    // Build complete leaderboard entries (names + colors + stats)
+    let mut entries: Vec<LeaderboardEntry> = game_view
+        .players
+        .iter()
+        .map(|player| {
+            let player_data = players_by_id.get(&(player.id as usize));
+
+            let name = player_data.map(|p| if p.name.is_empty() { if p.id == game.player_manager.client_player_id { "Player".to_string() } else { format!("Nation {}", p.id) } } else { p.name.clone() }).unwrap_or_else(|| format!("Nation {}", player.id));
+
+            let color = player_data.map(|p| rgba_to_hex(p.color.to_rgba())).unwrap_or_else(|| "808080".to_string()); // Gray fallback
+
+            let territory_percent = if total_land_tiles > 0 { player.tile_count as f32 / total_land_tiles as f32 } else { 0.0 };
+
+            LeaderboardEntry { id: player.id, name, color, tile_count: player.tile_count, troops: player.troops, territory_percent }
+        })
+        .collect();
+
+    // Sort by tile count descending
+    entries.sort_by(|a, b| b.tile_count.cmp(&a.tile_count));
+
+    Some(LeaderboardSnapshot { turn: game.turn_number, total_land_tiles, entries, client_player_id: game.player_manager.client_player_id as u16 })
+}
+
+/// Bevy system that emits leaderboard snapshot events
+pub fn emit_leaderboard_snapshot_system(game_view: Res<GameView>, game: Res<GameInstance>, mut last_digest: ResMut<LastLeaderboardDigest>, mut throttle: ResMut<LeaderboardThrottle>, mut backend_messages: MessageWriter<BackendMessage>) {
+    let _span = tracing::debug_span!("emit_leaderboard_snapshot").entered();
+
+    // Check if enough time has passed since last emission
+    let now = Instant::now();
+    let should_emit = throttle.last_emission.map(|last| now.duration_since(last) >= throttle.throttle_duration).unwrap_or(true); // Emit on first call
+
+    if !should_emit {
+        return;
+    }
+
+    if let Some(snapshot) = build_leaderboard_snapshot(&game_view, &game, &mut last_digest) {
+        backend_messages.write(BackendMessage::LeaderboardSnapshot(snapshot));
+        throttle.last_emission = Some(now);
+    }
+}
+
+/// Build an attacks update payload from current game state
+/// Always returns the current state (digest is used to prevent duplicate emissions)
+pub fn build_attacks_update(game: &GameInstance, client_player_id: usize, last_digest: &mut LastAttacksDigest) -> Option<AttacksUpdatePayload> {
+    // Get attacks for the client player
+    let raw_attacks = game.active_attacks.get_attacks_for_player(client_player_id);
+
+    // Build current digest for comparison
+    let current_entries: Vec<(usize, Option<usize>, u32, u64, bool)> = raw_attacks.iter().map(|&(attacker_id, target_id, troops, start_turn, is_outgoing)| (attacker_id, target_id, troops as u32, start_turn, is_outgoing)).collect();
+
+    // Check if anything has changed
+    if current_entries == last_digest.entries {
+        return None; // No changes
+    }
+
+    // Update digest
+    last_digest.entries = current_entries;
+    last_digest.turn = game.turn_number;
+
+    // Build attack entries
+    let entries: Vec<AttackEntry> = raw_attacks.into_iter().map(|(attacker_id, target_id, troops, start_turn, is_outgoing)| AttackEntry { attacker_id: attacker_id as u16, target_id: target_id.map(|id| id as u16), troops: troops as u32, start_turn, is_outgoing }).collect();
+
+    Some(AttacksUpdatePayload { turn: game.turn_number, entries })
+}
+
+/// Bevy system that emits attacks update events
+pub fn emit_attacks_update_system(game: Res<GameInstance>, mut last_digest: ResMut<LastAttacksDigest>, mut backend_messages: MessageWriter<BackendMessage>) {
+    let _span = tracing::debug_span!("emit_attacks_update").entered();
+    let client_player_id = game.player_manager.client_player_id;
+
+    if let Some(payload) = build_attacks_update(&game, client_player_id, &mut last_digest) {
+        backend_messages.write(BackendMessage::AttacksUpdate(payload));
+    }
+}

crates/borders-core/src/ui/mod.rs

@@ -0,0 +1,104 @@
+//! UI/Frontend module for rendering and user interaction
+//!
+//! This module contains all frontend-related concerns including:
+//! - Protocol definitions for frontend-backend communication
+//! - Input handling
+//! - Leaderboard management
+//! - Platform transport abstraction
+
+pub mod input;
+pub mod leaderboard;
+pub mod plugin;
+pub mod protocol;
+pub mod transport;
+
+// Re-export commonly used types
+pub use input::{InputEvent, InputState, KeyCode, MouseButton, TileCoord, WorldPos};
+pub use leaderboard::{LastAttacksDigest, LastLeaderboardDigest, LeaderboardThrottle, build_attacks_update, build_leaderboard_snapshot, emit_attacks_update_system, emit_leaderboard_snapshot_system};
+pub use plugin::FrontendPlugin;
+pub use protocol::{AttackEntry, AttacksUpdatePayload, BackendMessage, CameraCommand, CameraStateUpdate, FrontendMessage, GameOutcome, LeaderboardEntry, LeaderboardSnapshot, MapQuery, MapQueryResponse, PaletteInit, RenderInit, RenderInputEvent, RgbColor, ShipUpdateVariant, ShipsUpdatePayload, SpawnCountdown, TerrainInit, TerrainPalette, TerrainType, TerritoryDelta, TerritorySnapshot, TileChange};
+pub use transport::{FrontendTransport, RenderBridge, handle_camera_update, handle_render_input};
+
+use crate::networking::GameView;
+use bevy_ecs::prelude::*;
+use std::collections::HashMap;
+
+/// Resource to track currently highlighted nation for visual feedback
+#[derive(Resource, Default, Debug)]
+pub struct NationHighlightState {
+    pub highlighted_nation: Option<u16>,
+}
+
+/// System that tracks hovered nation and emits highlight events
+pub fn emit_nation_highlight_system(input_state: NonSend<std::sync::Arc<std::sync::Mutex<InputState>>>, game_view: Res<GameView>, mut highlight_state: ResMut<NationHighlightState>, mut backend_messages: MessageWriter<BackendMessage>) {
+    let Ok(input) = input_state.lock() else {
+        return;
+    };
+
+    let new_highlighted = if let Some(tile_coord) = input.cursor_tile() {
+        let tile_index = tile_coord.to_index(game_view.width);
+        let owner_id = game_view.get_owner(tile_index);
+
+        // Water (65535) and unclaimed (65534) should clear highlight
+        if owner_id >= 65534 { None } else { Some(owner_id) }
+    } else {
+        None
+    };
+
+    // Only emit if highlight changed
+    if new_highlighted != highlight_state.highlighted_nation {
+        highlight_state.highlighted_nation = new_highlighted;
+        backend_messages.write(BackendMessage::HighlightNation { nation_id: new_highlighted });
+    }
+}
+
+/// Resource to track previous ship states for delta updates
+#[derive(Resource, Default)]
+pub struct ShipStateTracker {
+    /// Map of ship ID to current_path_index
+    ship_indices: HashMap<u32, u32>,
+}
+
+/// System that emits ship update variants to the frontend (delta-based)
+/// - Create: sent when ship first appears
+/// - Move: sent only when current_path_index changes
+/// - Destroy: sent when ship disappears
+pub fn emit_ships_update_system(game_view: Res<GameView>, mut ship_tracker: ResMut<ShipStateTracker>, mut backend_messages: MessageWriter<BackendMessage>) {
+    let current_ship_ids: std::collections::HashSet<u32> = game_view.ships.iter().map(|s| s.id).collect();
+
+    let mut updates = Vec::new();
+
+    // Detect destroyed ships
+    for &ship_id in ship_tracker.ship_indices.keys() {
+        if !current_ship_ids.contains(&ship_id) {
+            updates.push(ShipUpdateVariant::Destroy { id: ship_id });
+        }
+    }
+
+    // Detect new ships and moved ships
+    for ship in &game_view.ships {
+        match ship_tracker.ship_indices.get(&ship.id) {
+            None => {
+                // New ship - send Create
+                updates.push(ShipUpdateVariant::Create { id: ship.id, owner_id: ship.owner_id, path: ship.path.clone(), troops: ship.troops });
+                ship_tracker.ship_indices.insert(ship.id, ship.path_progress);
+            }
+            Some(&prev_index) if prev_index != ship.path_progress => {
+                // Ship moved to next tile - send Move
+                updates.push(ShipUpdateVariant::Move { id: ship.id, current_path_index: ship.path_progress });
+                ship_tracker.ship_indices.insert(ship.id, ship.path_progress);
+            }
+            _ => {
+                // No change, do nothing
+            }
+        }
+    }
+
+    // Clean up destroyed ships from tracker
+    ship_tracker.ship_indices.retain(|id, _| current_ship_ids.contains(id));
+
+    // Only send if there are updates
+    if !updates.is_empty() {
+        backend_messages.write(BackendMessage::ShipsUpdate(ShipsUpdatePayload { turn: game_view.turn_number, updates }));
+    }
+}

crates/borders-core/src/ui/plugin.rs

@@ -0,0 +1,50 @@
+//! Frontend plugin for UI/rendering integration
+//!
+//! This module provides the FrontendPlugin which handles all frontend communication
+//! including rendering, input, and UI updates.
+
+use bevy_ecs::prelude::*;
+use bevy_ecs::schedule::common_conditions::resource_exists;
+
+use crate::app::{App, Plugin, Update};
+use crate::networking::GameView;
+use crate::ui::protocol::{BackendMessage, FrontendMessage};
+use crate::ui::transport::{FrontendTransport, RenderBridge, emit_backend_messages_system, ingest_frontend_messages_system, send_initial_render_data, stream_territory_deltas};
+
+/// Plugin to add frontend communication and UI systems to Bevy
+pub struct FrontendPlugin<T: FrontendTransport> {
+    transport: T,
+}
+
+impl<T: FrontendTransport> FrontendPlugin<T> {
+    pub fn new(transport: T) -> Self {
+        Self { transport }
+    }
+}
+
+impl<T: FrontendTransport> Plugin for FrontendPlugin<T> {
+    fn build(&self, app: &mut App) {
+        // Register message event types
+        app.add_message::<BackendMessage>();
+        app.add_message::<FrontendMessage>();
+
+        // Insert the bridge resource
+        app.insert_resource(RenderBridge::new(self.transport.clone()));
+
+        // Add render systems
+        app.add_systems(Update, (send_initial_render_data::<T>.run_if(resource_exists::<GameView>), stream_territory_deltas::<T>.run_if(resource_exists::<GameView>)).chain());
+
+        // Add communication systems
+        app.add_systems(Update, (emit_backend_messages_system::<T>, ingest_frontend_messages_system::<T>, reset_bridge_on_quit_system::<T>));
+    }
+}
+
+/// System to reset the render bridge when a game is quit
+/// This ensures fresh initialization data is sent when starting a new game
+fn reset_bridge_on_quit_system<T: FrontendTransport>(game_view: Option<Res<GameView>>, mut bridge: ResMut<RenderBridge<T>>) {
+    // If GameView doesn't exist but bridge is initialized, reset it
+    if game_view.is_none() && bridge.initialized {
+        bridge.reset();
+        tracing::debug!("RenderBridge reset - ready for next game initialization");
+    }
+}

crates/borders-core/src/ui/protocol.rs

@@ -0,0 +1,518 @@
+//! Protocol for frontend-backend communication
+//!
+//! This module defines the bidirectional message protocol used for communication
+//! between the game core (Bevy/Rust) and the frontend (PixiJS/TypeScript).
+
+use bevy_ecs::message::Message;
+use serde::{Deserialize, Serialize};
+
+/// All messages sent from backend to frontend
+#[derive(Debug, Clone, Serialize, Deserialize, Message)]
+#[serde(tag = "msg_type")]
+pub enum BackendMessage {
+    /// Atomic initialization message containing terrain, palette, and initial territories
+    RenderInit(RenderInit),
+
+    /// Full territory snapshot (typically only sent at initialization)
+    TerritorySnapshot(TerritorySnapshot),
+    /// Incremental territory changes (sent each turn)
+    TerritoryDelta(TerritoryDelta),
+
+    /// Initial terrain data (typically sent once, now part of RenderInit)
+    TerrainInit(TerrainInit),
+    /// Terrain color palette (typically sent once, now part of RenderInit)
+    TerrainPalette(TerrainPalette),
+    /// Player color palette (typically sent once, now part of RenderInit)
+    PaletteInit(PaletteInit),
+
+    /// Camera control commands from backend to frontend
+    CameraCommand(CameraCommand),
+
+    /// Response to map queries
+    MapQueryResponse(MapQueryResponse),
+
+    /// Complete leaderboard snapshot (includes names, colors, and stats)
+    LeaderboardSnapshot(LeaderboardSnapshot),
+    /// Dynamic attacks updates
+    AttacksUpdate(AttacksUpdatePayload),
+    /// Active ships on the map
+    ShipsUpdate(ShipsUpdatePayload),
+    /// Game has ended with the specified outcome
+    GameEnded { outcome: GameOutcome },
+    /// Spawn phase update
+    /// - countdown: None = phase active, waiting for first spawn
+    /// - countdown: Some = countdown in progress with epoch timestamp
+    SpawnPhaseUpdate { countdown: Option<SpawnCountdown> },
+    /// Spawn phase has ended, game is now active
+    SpawnPhaseEnded,
+    /// Highlight a specific nation (None to clear)
+    HighlightNation { nation_id: Option<u16> },
+}
+
+/// All messages sent from frontend to backend
+#[derive(Debug, Clone, Serialize, Deserialize, Message)]
+#[serde(tag = "msg_type")]
+pub enum FrontendMessage {
+    /// Input event (mouse clicks, keyboard, hover)
+    InputEvent(RenderInputEvent),
+
+    /// Camera state update from frontend
+    CameraStateUpdate(CameraStateUpdate),
+
+    /// Query about the map state
+    MapQuery(MapQuery),
+
+    /// Start a new game
+    StartGame,
+    /// Quit the current game and return to menu
+    QuitGame,
+    /// Pause the game (local/singleplayer only)
+    PauseGame,
+    /// Resume the game (local/singleplayer only)
+    ResumeGame,
+    /// Set attack ratio (percentage of troops to use when attacking)
+    SetAttackRatio { ratio: f32 },
+}
+
+/// Terrain types for map tiles
+#[derive(Debug, Clone, Copy, Serialize, Deserialize, PartialEq, Eq)]
+#[repr(u8)]
+pub enum TerrainType {
+    Water = 0,
+    Land = 1,
+    Mountain = 2,
+}
+
+/// Initial terrain data for the entire map
+#[derive(Debug, Clone, Serialize, Deserialize)]
+pub struct TerrainInit {
+    /// Map width in tiles
+    pub width: u32,
+    /// Map height in tiles
+    pub height: u32,
+    /// Tile type IDs (one u8 per tile, referencing TerrainPalette)
+    /// Each value is an index into the terrain_palette colors array
+    #[serde(with = "serde_bytes")]
+    pub terrain_data: Vec<u8>,
+}
+
+impl TerrainInit {
+    /// Create terrain data from tile type IDs
+    pub fn from_tile_ids(width: u32, height: u32, tile_ids: Vec<u8>) -> Self {
+        assert_eq!(tile_ids.len(), (width * height) as usize, "Terrain data size mismatch");
+        Self { width, height, terrain_data: tile_ids }
+    }
+
+    /// Create terrain data from a legacy terrain enum array (for backward compatibility)
+    pub fn from_terrain(width: u32, height: u32, terrain: &[TerrainType]) -> Self {
+        let terrain_data: Vec<u8> = terrain.iter().map(|&t| t as u8).collect();
+        Self { width, height, terrain_data }
+    }
+
+    /// Extract tile type ID for a specific tile
+    pub fn get_tile_id(&self, index: usize) -> u8 {
+        self.terrain_data.get(index).copied().unwrap_or(0)
+    }
+}
+
+/// Terrain palette defining colors for each terrain shade/type
+#[derive(Debug, Clone, Serialize, Deserialize)]
+pub struct TerrainPalette {
+    /// Color definitions for each terrain shade
+    /// Index in this array corresponds to the shade value in terrain_data
+    pub colors: Vec<RgbColor>,
+}
+
+/// A single tile change in the territory map
+#[derive(Debug, Clone, Copy, Serialize, Deserialize)]
+pub struct TileChange {
+    /// Tile index (row * width + col)
+    pub index: u32,
+    /// New owner player ID (0 = unclaimed)
+    pub owner_id: u16,
+}
+
+/// Delta update containing changed tiles for efficient streaming
+#[derive(Debug, Clone, Serialize, Deserialize)]
+pub struct TerritoryDelta {
+    /// Turn number this delta applies to
+    pub turn: u64,
+    /// List of changed tiles since last update
+    pub changes: Vec<TileChange>,
+}
+
+/// Full territory snapshot for initial state (sparse binary format)
+#[derive(Debug, Clone, Serialize, Deserialize)]
+pub struct TerritorySnapshot {
+    /// Turn number for this snapshot
+    pub turn: u64,
+    /// Binary-encoded sparse territory data
+    /// Format: [count:4][changes...]
+    /// where changes = [index:4][owner:2] repeated count times
+    /// All tiles not in this list default to owner_id=0 (unclaimed)
+    #[serde(with = "serde_bytes")]
+    pub data: Vec<u8>,
+}
+
+impl TerritorySnapshot {
+    /// Create sparse binary snapshot from full territory array
+    /// Only includes claimed tiles (owner_id != 0)
+    pub fn encode(turn: u64, territories: &[u16]) -> Self {
+        // Collect claimed tiles (non-zero owner IDs)
+        let claimed_tiles: Vec<(u32, u16)> = territories.iter().enumerate().filter(|&(_, &owner)| owner != 0).map(|(index, &owner)| (index as u32, owner)).collect();
+
+        let count = claimed_tiles.len() as u32;
+        let mut data = Vec::with_capacity(4 + claimed_tiles.len() * 6);
+
+        // Encode count (4 bytes)
+        data.extend_from_slice(&count.to_le_bytes());
+
+        // Encode each claimed tile (6 bytes each)
+        for (index, owner) in claimed_tiles {
+            data.extend_from_slice(&index.to_le_bytes());
+            data.extend_from_slice(&owner.to_le_bytes());
+        }
+
+        Self { turn, data }
+    }
+
+    /// Decode binary snapshot back to list of claimed tiles
+    /// Returns list of (tile_index, owner_id) pairs
+    pub fn decode(&self) -> Option<Vec<(u32, u16)>> {
+        if self.data.len() < 4 {
+            return None; // Not enough data for count
+        }
+
+        let count = u32::from_le_bytes([self.data[0], self.data[1], self.data[2], self.data[3]]) as usize;
+
+        let expected_size = 4 + count * 6;
+        if self.data.len() != expected_size {
+            return None; // Invalid size
+        }
+
+        let mut tiles = Vec::with_capacity(count);
+        for i in 0..count {
+            let offset = 4 + i * 6;
+            let index = u32::from_le_bytes([self.data[offset], self.data[offset + 1], self.data[offset + 2], self.data[offset + 3]]);
+            let owner = u16::from_le_bytes([self.data[offset + 4], self.data[offset + 5]]);
+            tiles.push((index, owner));
+        }
+
+        Some(tiles)
+    }
+}
+
+/// Binary format for efficient territory delta streaming (Tauri)
+/// This is for the pixel streaming channel, separate from JSON messages
+#[derive(Debug)]
+pub struct BinaryTerritoryDelta {
+    /// Raw bytes: [turn:8][count:4][changes...]
+    /// Each change: [index:4][owner:2] = 6 bytes
+    pub data: Vec<u8>,
+}
+
+impl BinaryTerritoryDelta {
+    /// Create binary delta from territory changes
+    pub fn encode(turn: u64, changes: &[TileChange]) -> Vec<u8> {
+        let count = changes.len() as u32;
+        let mut data = Vec::with_capacity(12 + changes.len() * 6);
+
+        // Header: turn (8 bytes) + count (4 bytes)
+        data.extend_from_slice(&turn.to_le_bytes());
+        data.extend_from_slice(&count.to_le_bytes());
+
+        // Changes: each is index (4 bytes) + owner (2 bytes)
+        for change in changes {
+            data.extend_from_slice(&change.index.to_le_bytes());
+            data.extend_from_slice(&change.owner_id.to_le_bytes());
+        }
+
+        data
+    }
+
+    /// Decode binary delta back to structured format
+    pub fn decode(data: &[u8]) -> Option<(u64, Vec<TileChange>)> {
+        if data.len() < 12 {
+            return None; // Not enough data for header
+        }
+
+        let turn = u64::from_le_bytes([data[0], data[1], data[2], data[3], data[4], data[5], data[6], data[7]]);
+
+        let count = u32::from_le_bytes([data[8], data[9], data[10], data[11]]) as usize;
+
+        let expected_size = 12 + count * 6;
+        if data.len() != expected_size {
+            return None; // Invalid size
+        }
+
+        let mut changes = Vec::with_capacity(count);
+        for i in 0..count {
+            let offset = 12 + i * 6;
+            let index = u32::from_le_bytes([data[offset], data[offset + 1], data[offset + 2], data[offset + 3]]);
+            let owner_id = u16::from_le_bytes([data[offset + 4], data[offset + 5]]);
+            changes.push(TileChange { index, owner_id });
+        }
+
+        Some((turn, changes))
+    }
+}
+
+/// RGB color for player palette
+#[derive(Debug, Clone, Copy, Serialize, Deserialize)]
+pub struct RgbColor {
+    pub r: u8,
+    pub g: u8,
+    pub b: u8,
+}
+
+/// Initial palette data mapping player IDs to colors
+#[derive(Debug, Clone, Serialize, Deserialize)]
+pub struct PaletteInit {
+    /// Player ID to color mapping
+    /// Index in the vec corresponds to player_id
+    pub colors: Vec<RgbColor>,
+}
+
+/// Commands sent from backend to control the camera
+#[derive(Debug, Clone, Serialize, Deserialize, bevy_ecs::message::Message)]
+#[serde(tag = "type")]
+pub enum CameraCommand {
+    /// Center camera on a specific tile
+    CenterOnTile {
+        tile_index: u32,
+        #[serde(default)]
+        animate: bool,
+    },
+    /// Highlight a rectangular region
+    HighlightRegion {
+        x: u32,
+        y: u32,
+        width: u32,
+        height: u32,
+        #[serde(default = "default_highlight_duration")]
+        duration_ms: u32,
+    },
+    /// Set camera zoom level
+    SetZoom {
+        zoom: f32,
+        #[serde(default)]
+        animate: bool,
+    },
+    /// Pan camera by offset
+    PanBy {
+        dx: f32,
+        dy: f32,
+        #[serde(default)]
+        animate: bool,
+    },
+}
+
+fn default_highlight_duration() -> u32 {
+    3000 // 3 seconds
+}
+
+/// Camera state update sent from frontend to backend
+#[derive(Debug, Clone, Serialize, Deserialize)]
+pub struct CameraStateUpdate {
+    /// Current camera X position (world coordinates)
+    pub x: f32,
+    /// Current camera Y position (world coordinates)
+    pub y: f32,
+    /// Current zoom level (1.0 = normal)
+    pub zoom: f32,
+}
+
+/// Queries sent from frontend to backend about the map
+#[derive(Debug, Clone, Serialize, Deserialize)]
+#[serde(tag = "type")]
+pub enum MapQuery {
+    /// Get owner of tile at world coordinates
+    GetOwnerAt { x: f32, y: f32 },
+    /// Get detailed tile info by index
+    GetTileInfo { tile_index: u32 },
+    /// Find any tile owned by player (for camera centering)
+    FindPlayerTerritory { player_id: u16 },
+    /// Convert screen coordinates to tile index
+    ScreenToTile { screen_x: f32, screen_y: f32 },
+}
+
+/// Response to map queries
+#[derive(Debug, Clone, Serialize, Deserialize)]
+#[serde(tag = "type")]
+pub enum MapQueryResponse {
+    /// Response to GetOwnerAt
+    Owner { owner_id: u16, tile_index: Option<u32> },
+    /// Response to GetTileInfo
+    TileInfo { tile_index: u32, owner_id: u16, terrain: TerrainType, troops: u32 },
+    /// Response to FindPlayerTerritory
+    PlayerTerritory { tile_index: Option<u32> },
+    /// Response to ScreenToTile
+    TileIndex { index: Option<u32> },
+}
+
+/// Input event sent from frontend to backend
+#[derive(Debug, Clone, Serialize, Deserialize)]
+#[serde(tag = "type")]
+pub enum RenderInputEvent {
+    /// Mouse click on the map
+    MapClick {
+        /// Tile index clicked (if over a valid tile)
+        tile_index: Option<u32>,
+        /// World coordinates of click
+        world_x: f32,
+        world_y: f32,
+        /// Mouse button (0=left, 1=middle, 2=right)
+        button: u8,
+    },
+    /// Key press event
+    KeyPress {
+        /// Key code as string (e.g., "KeyC", "Digit1")
+        key: String,
+        /// Whether key is pressed (true) or released (false)
+        pressed: bool,
+    },
+    /// Mouse moved over map
+    MapHover {
+        /// Tile index under cursor (if any)
+        tile_index: Option<u32>,
+        /// World coordinates
+        world_x: f32,
+        world_y: f32,
+    },
+}
+
+/// Atomic initialization message containing all data needed to start rendering
+/// This ensures terrain, palette, and initial territory state arrive together
+#[derive(Debug, Clone, Serialize, Deserialize)]
+pub struct RenderInit {
+    pub terrain: TerrainInit,
+    pub terrain_palette: TerrainPalette,
+    pub palette: PaletteInit,
+    pub initial_territories: TerritorySnapshot,
+}
+
+/// Unified leaderboard entry containing both static and dynamic data
+#[derive(Debug, Clone, Serialize, Deserialize)]
+pub struct LeaderboardEntry {
+    pub id: u16,
+    pub name: String,
+    pub color: String, // Hex color without alpha, e.g. "0A44FF"
+    pub tile_count: u32,
+    pub troops: u32,
+    pub territory_percent: f32,
+}
+
+/// Complete leaderboard snapshot (replaces separate Init/Update)
+#[derive(Debug, Clone, Serialize, Deserialize)]
+pub struct LeaderboardSnapshot {
+    pub turn: u64,
+    pub total_land_tiles: u32,
+    pub entries: Vec<LeaderboardEntry>,
+    pub client_player_id: u16,
+}
+
+/// Outcome of the game
+#[derive(Debug, Clone, Serialize, Deserialize)]
+pub enum GameOutcome {
+    /// Player won the game
+    Victory,
+    /// Player lost the game
+    Defeat,
+}
+
+/// Single attack entry for attacks UI
+#[derive(Debug, Clone, Serialize, Deserialize)]
+pub struct AttackEntry {
+    pub attacker_id: u16,
+    pub target_id: Option<u16>, // None for unclaimed territory
+    pub troops: u32,
+    pub start_turn: u64,
+    pub is_outgoing: bool,
+}
+
+/// Attacks update payload
+#[derive(Debug, Clone, Serialize, Deserialize)]
+pub struct AttacksUpdatePayload {
+    pub turn: u64,
+    pub entries: Vec<AttackEntry>,
+}
+
+/// Ships update payload with lifecycle variants
+#[derive(Debug, Clone, Serialize, Deserialize)]
+pub struct ShipsUpdatePayload {
+    pub turn: u64,
+    pub updates: Vec<ShipUpdateVariant>,
+}
+
+/// Ship update variants for efficient delta updates
+/// NOTE: SHIP_TICKS_PER_TILE (1) must be synchronized between backend and frontend
+#[derive(Debug, Clone, Serialize, Deserialize)]
+#[serde(tag = "type")]
+pub enum ShipUpdateVariant {
+    /// Ship created - full initial state
+    Create {
+        id: u32,
+        owner_id: u16,
+        path: Vec<u32>,
+        troops: u32, // Static value, currently unused for rendering
+    },
+    /// Ship moved to next tile in path
+    Move { id: u32, current_path_index: u32 },
+    /// Ship destroyed (arrived or cancelled)
+    Destroy { id: u32 },
+}
+
+// TODO: On client reconnection/late-join, send Create variants for all active ships
+
+/// Legacy ship data (deprecated - remove after migration)
+#[derive(Debug, Clone, Serialize, Deserialize)]
+#[deprecated(note = "Use ShipUpdateVariant instead")]
+pub struct ShipData {
+    pub id: u32,
+    pub owner_id: u16,
+    pub current_tile: u32,
+    pub target_tile: u32,
+    pub troops: u32,
+    pub path_progress: u32,
+    pub ticks_until_move: u32,
+}
+
+/// Countdown state for spawn phase
+#[derive(Debug, Clone, Serialize, Deserialize)]
+pub struct SpawnCountdown {
+    pub started_at_ms: u64,
+    pub duration_secs: f32,
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn test_terrain_tile_ids() {
+        let terrain = vec![TerrainType::Water, TerrainType::Land, TerrainType::Mountain, TerrainType::Land, TerrainType::Water];
+
+        let init = TerrainInit::from_terrain(5, 1, &terrain);
+        assert_eq!(init.terrain_data.len(), 5);
+
+        assert_eq!(init.get_tile_id(0), TerrainType::Water as u8);
+        assert_eq!(init.get_tile_id(1), TerrainType::Land as u8);
+        assert_eq!(init.get_tile_id(2), TerrainType::Mountain as u8);
+        assert_eq!(init.get_tile_id(3), TerrainType::Land as u8);
+        assert_eq!(init.get_tile_id(4), TerrainType::Water as u8);
+    }
+
+    #[test]
+    fn test_binary_delta_encoding() {
+        let changes = vec![TileChange { index: 100, owner_id: 1 }, TileChange { index: 200, owner_id: 2 }, TileChange { index: 300, owner_id: 0 }];
+
+        let encoded = BinaryTerritoryDelta::encode(42, &changes);
+        assert_eq!(encoded.len(), 12 + 3 * 6);
+
+        let decoded = BinaryTerritoryDelta::decode(&encoded).unwrap();
+        assert_eq!(decoded.0, 42);
+        assert_eq!(decoded.1.len(), 3);
+        assert_eq!(decoded.1[0].index, 100);
+        assert_eq!(decoded.1[0].owner_id, 1);
+    }
+}

crates/borders-core/src/ui/transport.rs

@@ -0,0 +1,236 @@
+//! Shared render bridge infrastructure for platform-agnostic rendering
+//!
+//! This module provides the common logic for rendering bridges across platforms
+//! (WASM, Tauri, etc.), with platform-specific transport mechanisms abstracted
+//! behind the RenderBridgeTransport trait.
+
+use crate::TerrainData;
+use crate::networking::GameView;
+use crate::ui::protocol::{BackendMessage, BinaryTerritoryDelta, CameraStateUpdate, FrontendMessage, PaletteInit, RenderInit, RenderInputEvent, RgbColor, TerrainInit, TerrainPalette, TerritoryDelta, TerritorySnapshot, TileChange};
+use bevy_ecs::prelude::*;
+use tracing::{error, info, trace, warn};
+
+/// Trait for platform-specific frontend communication
+///
+/// This abstracts the actual mechanism for bidirectional frontend communication,
+/// allowing WASM (JS callbacks), Tauri (events), and other platforms to implement
+/// their own transport while sharing the core logic.
+pub trait FrontendTransport: Send + Sync + Clone + 'static {
+    /// Send a message from backend to frontend
+    fn send_backend_message(&self, message: &BackendMessage) -> Result<(), String>;
+
+    /// Send binary territory delta data (optional, mainly for Tauri)
+    ///
+    /// Default implementation does nothing - platforms that support
+    /// binary streaming can override this.
+    fn send_binary_delta(&self, _data: Vec<u8>) -> Result<(), String> {
+        Ok(()) // No-op by default
+    }
+
+    /// Try to receive a message from the frontend
+    ///
+    /// Returns `Some(message)` if a message is available, `None` if not.
+    /// This should be non-blocking and called frequently (e.g., every frame).
+    fn try_recv_frontend_message(&self) -> Option<FrontendMessage>;
+}
+
+/// Resource for managing frontend communication state
+#[derive(Resource)]
+pub struct RenderBridge<T: FrontendTransport> {
+    pub transport: T,
+    /// Track if we've sent initial data
+    pub(crate) initialized: bool,
+}
+
+impl<T: FrontendTransport> RenderBridge<T> {
+    pub fn new(transport: T) -> Self {
+        Self { transport, initialized: false }
+    }
+
+    /// Reset the bridge to allow re-initialization
+    /// This should be called when a game is quit to ensure fresh data is sent on next game start
+    pub fn reset(&mut self) {
+        self.initialized = false;
+    }
+}
+
+/// System to send initial render data (terrain, palette, initial territories)
+pub fn send_initial_render_data<T: FrontendTransport>(game_view: Option<Res<GameView>>, terrain_data: Option<Res<TerrainData>>, mut bridge: Option<ResMut<RenderBridge<T>>>) {
+    let Some(game_view) = game_view else {
+        trace!("send_initial_render_data: GameView not available yet");
+        return;
+    };
+
+    let Some(terrain_data) = terrain_data else {
+        trace!("send_initial_render_data: TerrainData not available yet");
+        return;
+    };
+
+    let Some(ref mut bridge) = bridge else {
+        error!("send_initial_render_data: RenderBridge not available");
+        return;
+    };
+
+    // Early return if already initialized - prevents duplicate sends
+    if bridge.initialized {
+        return;
+    }
+
+    // Don't send initial data for empty game view
+    if game_view.width == 0 || game_view.height == 0 || game_view.players.is_empty() {
+        trace!("send_initial_render_data: GameView not yet populated, waiting...");
+        return;
+    }
+
+    info!("Building atomic RenderInit message (map: {}x{}, {} players)", game_view.width, game_view.height, game_view.players.len());
+
+    // Build terrain component from TerrainData
+    let width = game_view.width;
+    let height = game_view.height;
+    let tile_ids = terrain_data.get_tile_ids().to_vec();
+    let terrain = TerrainInit::from_tile_ids(width, height, tile_ids);
+
+    // Build terrain palette from TerrainData
+    let palette_colors = terrain_data.get_terrain_palette_colors();
+    let terrain_palette = TerrainPalette { colors: palette_colors.into_iter().map(|[r, g, b]| RgbColor { r, g, b }).collect() };
+
+    info!("Terrain palette: {} colors", terrain_palette.colors.len());
+
+    // Build palette component
+    // Allocate only enough space for active players + a small buffer
+    // This avoids the wasteful 65K allocation (1MB+ of memory)
+    let max_player_id = game_view.players.iter().map(|p| p.id).max().unwrap_or(0) as usize;
+
+    // Allocate palette size as: max(256, max_player_id + 1) to handle typical player counts
+    // Most games have <100 players, so this is ~256 bytes instead of 1MB+
+    let palette_size = (max_player_id + 1).max(256);
+    let mut colors = vec![RgbColor { r: 0, g: 0, b: 0 }; palette_size];
+
+    for player in &game_view.players {
+        // Player color is already in [r, g, b, a] format as f32
+        colors[player.id as usize] = RgbColor { r: (player.color[0] * 255.0) as u8, g: (player.color[1] * 255.0) as u8, b: (player.color[2] * 255.0) as u8 };
+    }
+    let palette = PaletteInit { colors };
+
+    // Build initial territory snapshot (sparse binary format)
+    let initial_territories = TerritorySnapshot::encode(game_view.turn_number, &game_view.territories);
+
+    // Create atomic initialization message
+    let render_init = RenderInit { terrain, terrain_palette, palette, initial_territories };
+
+    // Send single atomic message - all or nothing
+    if let Err(e) = bridge.transport.send_backend_message(&BackendMessage::RenderInit(render_init)) {
+        error!("Failed to send atomic RenderInit message: {}", e);
+        return;
+    }
+
+    // Only mark as initialized if send succeeded
+    bridge.initialized = true;
+    info!("Atomic RenderInit sent successfully");
+}
+
+/// System to detect and stream territory changes
+pub fn stream_territory_deltas<T: FrontendTransport>(game_view: Option<Res<GameView>>, bridge: Option<Res<RenderBridge<T>>>) {
+    let Some(game_view) = game_view else {
+        return; // GameView not ready yet
+    };
+
+    let Some(bridge) = bridge else {
+        return; // Bridge not initialized
+    };
+
+    // Gate: Don't send deltas until initial render data has been sent
+    if !bridge.initialized {
+        return;
+    }
+
+    // Skip if GameView hasn't changed
+    if !game_view.is_changed() {
+        return;
+    }
+
+    let _span = tracing::debug_span!("stream_territory_deltas").entered();
+
+    // Use efficient changed_tiles from TerritoryManager's ChangeBuffer instead of scanning
+    if !game_view.changed_tiles.is_empty() {
+        let turn = game_view.turn_number;
+
+        // Build delta from the pre-tracked changes
+        let changes: Vec<TileChange> = game_view.changed_tiles.iter().map(|&index| TileChange { index: index as u32, owner_id: game_view.territories[index] }).collect();
+
+        // Send binary format for platforms that support it (e.g., Tauri)
+        let binary_data = BinaryTerritoryDelta::encode(turn, &changes);
+        if let Err(e) = bridge.transport.send_binary_delta(binary_data) {
+            error!("Failed to send binary territory delta: {}", e);
+        }
+
+        // Send structured format
+        let delta = TerritoryDelta { turn, changes };
+        if let Err(e) = bridge.transport.send_backend_message(&BackendMessage::TerritoryDelta(delta)) {
+            error!("Failed to send territory delta: {}", e);
+        }
+    }
+}
+
+/// Handle render input events from the frontend
+///
+/// This function processes input events and updates the shared InputState.
+/// It should be called from platform-specific command handlers.
+pub fn handle_render_input(event: &RenderInputEvent, input_state: &mut crate::ui::input::InputState, map_width: u32) -> Result<(), String> {
+    match event {
+        RenderInputEvent::MapClick { tile_index, world_x, world_y, button } => {
+            if let Some(button) = crate::ui::input::MouseButton::from_u8(*button) {
+                let world_pos = crate::ui::input::WorldPos { x: *world_x, y: *world_y };
+
+                let tile_coord = tile_index.map(|idx| crate::ui::input::TileCoord::from_index(idx as usize, map_width));
+
+                input_state.handle_event(crate::ui::input::InputEvent::MouseButton { button, state: crate::ui::input::ButtonState::Released, world_pos: Some(world_pos), tile: tile_coord });
+            }
+        }
+        RenderInputEvent::KeyPress { key, pressed } => {
+            if let Some(key_code) = crate::ui::input::KeyCode::from_string(key) {
+                let button_state = if *pressed { crate::ui::input::ButtonState::Pressed } else { crate::ui::input::ButtonState::Released };
+
+                input_state.handle_event(crate::ui::input::InputEvent::KeyPress { key: key_code, state: button_state });
+            }
+        }
+        RenderInputEvent::MapHover { tile_index, world_x, world_y } => {
+            let world_pos = crate::ui::input::WorldPos { x: *world_x, y: *world_y };
+
+            let tile_coord = tile_index.map(|idx| crate::ui::input::TileCoord::from_index(idx as usize, map_width));
+
+            input_state.handle_event(crate::ui::input::InputEvent::MouseMove {
+                world_pos,
+                screen_pos: crate::ui::input::ScreenPos { x: 0.0, y: 0.0 }, // Not used
+                tile: tile_coord,
+            });
+        }
+    }
+
+    Ok(())
+}
+
+/// Handle camera state updates from the frontend
+///
+/// This is a simple wrapper for consistency. Camera state is typically stored
+/// in a shared Arc<Mutex<Option<CameraStateUpdate>>> resource.
+pub fn handle_camera_update(update: CameraStateUpdate, camera_state: &mut Option<CameraStateUpdate>) -> Result<(), String> {
+    *camera_state = Some(update);
+    Ok(())
+}
+
+/// System that reads BackendMessage events and sends them through the transport
+pub(crate) fn emit_backend_messages_system<T: FrontendTransport>(mut events: MessageReader<BackendMessage>, bridge: Res<RenderBridge<T>>) {
+    for event in events.read() {
+        if let Err(e) = bridge.transport.send_backend_message(event) {
+            warn!("Failed to send backend message through transport: {}", e);
+        }
+    }
+}
+
+/// System that polls the transport for incoming frontend messages and emits them as events
+pub(crate) fn ingest_frontend_messages_system<T: FrontendTransport>(mut messages: MessageWriter<FrontendMessage>, bridge: Res<RenderBridge<T>>) {
+    while let Some(message) = bridge.transport.try_recv_frontend_message() {
+        messages.write(message);
+    }
+}

crates/borders-core/tests/terrain.rs

@@ -0,0 +1,50 @@
+use borders_core::game::terrain::{MapManifest, MapMetadata, TerrainData, TileType};
+use borders_core::game::tilemap::TileMap;
+
+fn create_test_terrain(width: usize, height: usize) -> TerrainData {
+    let tile_types = vec![TileType { name: "water".to_string(), color_base: "blue".to_string(), color_variant: 0, conquerable: false, navigable: true, expansion_time: 255, expansion_cost: 255 }, TileType { name: "land".to_string(), color_base: "green".to_string(), color_variant: 0, conquerable: true, navigable: false, expansion_time: 50, expansion_cost: 50 }];
+
+    let mut terrain_data_raw = vec![0; width * height];
+    terrain_data_raw[5] = 0x80; // Make position 5 land
+    terrain_data_raw[10] = 0x85; // Make position 10 land with magnitude 5
+
+    let tiles: Vec<u8> = terrain_data_raw.iter().map(|&byte| if byte & 0x80 != 0 { 1 } else { 0 }).collect();
+
+    let terrain_data = TileMap::from_vec(width as u32, height as u32, terrain_data_raw);
+
+    TerrainData { _manifest: MapManifest { map: MapMetadata { width, height, num_land_tiles: 2 }, name: "Test".to_string(), nations: Vec::new() }, terrain_data, tiles, tile_types }
+}
+
+#[test]
+fn test_is_land() {
+    let terrain = create_test_terrain(10, 10);
+    assert!(!terrain.is_land((0, 0)));
+    assert!(terrain.is_land((5, 0)));
+}
+
+#[test]
+fn test_is_conquerable() {
+    let terrain = create_test_terrain(10, 10);
+    assert!(!terrain.is_conquerable((0, 0)));
+    assert!(terrain.is_conquerable((5, 0)));
+}
+
+#[test]
+fn test_is_navigable() {
+    let terrain = create_test_terrain(10, 10);
+    assert!(terrain.is_navigable((0, 0)));
+    assert!(!terrain.is_navigable((5, 0)));
+}
+
+#[test]
+fn test_terrain_magnitude() {
+    let terrain = create_test_terrain(10, 10);
+    assert_eq!(terrain.terrain_magnitude((0, 1)), 5);
+}
+
+#[test]
+fn test_expansion_properties() {
+    let terrain = create_test_terrain(10, 10);
+    assert_eq!(terrain.get_expansion_time((5, 0)), 50);
+    assert_eq!(terrain.get_expansion_cost((5, 0)), 50);
+}

crates/borders-desktop/.gitignore

@@ -0,0 +1,7 @@
+# Generated by Cargo
+# will have compiled files and executables
+/target/
+
+# Generated by Tauri
+# will have schema files for capabilities auto-completion
+/gen/schemas

crates/borders-desktop/Cargo.toml

@@ -0,0 +1,29 @@
+[package]
+name = "borders-desktop"
+version.workspace = true
+edition.workspace = true
+authors.workspace = true
+
+[features]
+default = []
+tracy = ["dep:tracing-tracy", "dep:tracy-client"]
+
+[build-dependencies]
+tauri-build = { version = "2", features = [] }
+
+[dependencies]
+bevy_ecs = { version = "0.17", default-features = false, features = ["std"] }
+borders-core = { path = "../borders-core", features = ["ui"] }
+serde = { version = "1", features = ["derive"] }
+serde_json = "1"
+tauri = { version = "2", features = [] }
+tauri-plugin-opener = "2"
+tauri-plugin-process = "2"
+tokio = { version = "1", features = ["time"] }
+tracing = "0.1"
+tracing-subscriber = { version = "0.3", features = ["env-filter"] }
+tracing-tracy = { version = "0.11", default-features = false, optional = true }
+tracy-client = { version = "0.18.2", optional = true }
+
+[package.metadata.cargo-machete]
+ignored = ["tauri-build"]

crates/borders-desktop/build.rs

@@ -0,0 +1,3 @@
+fn main() {
+    tauri_build::build()
+}

crates/borders-desktop/capabilities/default.json

@@ -0,0 +1,17 @@
+{
+  "$schema": "../gen/schemas/desktop-schema.json",
+  "identifier": "default",
+  "description": "Capability for the main window",
+  "windows": ["main"],
+  "permissions": [
+    "core:default",
+    {
+      "identifier": "opener:allow-open-url",
+      "allow": [
+        {
+          "url": "https://github.com/Xevion"
+        }
+      ]
+    }
+  ]
+}

crates/borders-desktop/src/analytics.rs

@@ -0,0 +1,51 @@
+use borders_core::telemetry::{self, TelemetryEvent};
+use serde::{Deserialize, Serialize};
+use std::collections::HashMap;
+use tauri::Manager;
+
+/// Analytics event from the frontend
+#[derive(Debug, Clone, Serialize, Deserialize)]
+pub struct AnalyticsEventPayload {
+    pub event: String,
+    #[serde(default)]
+    pub properties: HashMap<String, serde_json::Value>,
+}
+
+/// Tauri command to track analytics events from the frontend
+#[tauri::command]
+pub async fn track_analytics_event(payload: AnalyticsEventPayload) -> Result<(), String> {
+    tracing::debug!("Tracking analytics event: {}", payload.event);
+
+    let event = TelemetryEvent { event: payload.event, properties: payload.properties };
+
+    // Track the event asynchronously (Tauri handles the async context)
+    telemetry::track(event).await;
+
+    Ok(())
+}
+
+/// Tauri command to flush pending analytics events
+#[tauri::command]
+pub async fn flush_analytics() -> Result<(), String> {
+    if let Some(client) = telemetry::client() {
+        client.flush().await;
+        Ok(())
+    } else {
+        Err("Telemetry client not initialized".to_string())
+    }
+}
+
+/// Tauri command to request app exit
+///
+/// Simply closes the window - analytics flush happens in ExitRequested event handler
+#[tauri::command]
+pub async fn request_exit(app_handle: tauri::AppHandle) -> Result<(), String> {
+    tracing::debug!("Exit requested via command");
+
+    // Close the window (will trigger ExitRequested event → analytics flush)
+    if let Some(window) = app_handle.get_webview_window("main") {
+        window.close().map_err(|e| e.to_string())?;
+    }
+
+    Ok(())
+}

crates/borders-desktop/src/main.rs

@@ -0,0 +1,81 @@
+// Prevents additional console window on Windows in release, DO NOT REMOVE!!
+#![cfg_attr(not(debug_assertions), windows_subsystem = "windows")]
+
+use crate::plugin::{TauriPlugin, generate_tauri_context};
+use borders_core::app::App;
+use borders_core::time::Time;
+
+mod analytics;
+mod plugin;
+mod render_bridge;
+
+#[cfg_attr(mobile, tauri::mobile_entry_point)]
+pub fn run() {
+    let mut app = App::new();
+
+    // Initialize time tracking
+    app.insert_resource(Time::new());
+
+    TauriPlugin::new(|| tauri::Builder::default().plugin(tauri_plugin_opener::init()).plugin(tauri_plugin_process::init()).invoke_handler(tauri::generate_handler![render_bridge::send_frontend_message, render_bridge::handle_render_input, render_bridge::handle_camera_update, render_bridge::handle_map_query, render_bridge::get_game_state, analytics::track_analytics_event, analytics::flush_analytics, analytics::request_exit,]).build(generate_tauri_context()).expect("error while building tauri application")).build_and_run(app);
+}
+
+fn main() {
+    // Initialize tracing before Bevy
+    #[cfg(feature = "tracy")]
+    {
+        // Initialize Tracy profiler client
+        let _client = tracy_client::Client::start();
+
+        use tracing_subscriber::layer::SubscriberExt;
+
+        tracing::subscriber::set_global_default(tracing_subscriber::registry().with(tracing_tracy::TracyLayer::default())).expect("setup tracy layer");
+    }
+
+    #[cfg(not(feature = "tracy"))]
+    {
+        use tracing_subscriber::fmt::time::FormatTime;
+        use tracing_subscriber::layer::SubscriberExt;
+        use tracing_subscriber::util::SubscriberInitExt;
+
+        #[cfg(debug_assertions)]
+        let log_filter = "borders_core=debug,borders_protocol=debug,borders_desktop=debug,iron_borders=debug,info";
+
+        #[cfg(not(debug_assertions))]
+        let log_filter = "borders_core=warn,borders_protocol=warn,iron_borders=warn,error";
+
+        struct CustomTimeFormat;
+
+        impl FormatTime for CustomTimeFormat {
+            fn format_time(&self, w: &mut tracing_subscriber::fmt::format::Writer<'_>) -> std::fmt::Result {
+                let now = std::time::SystemTime::now().duration_since(std::time::UNIX_EPOCH).unwrap();
+                let total_secs = now.as_secs();
+                let nanos = now.subsec_nanos();
+
+                let secs_in_day = total_secs % 86400;
+                let hours = secs_in_day / 3600;
+                let minutes = (secs_in_day % 3600) / 60;
+                let seconds = secs_in_day % 60;
+                let millis = nanos / 1_000_000;
+                let micros = (nanos / 1_000) % 1_000;
+
+                write!(w, "{:02}:{:02}:{:02}.{:03}{:03}", hours, minutes, seconds, millis, micros)
+            }
+        }
+
+        tracing_subscriber::registry().with(tracing_subscriber::EnvFilter::new(log_filter)).with(tracing_subscriber::fmt::layer().with_timer(CustomTimeFormat)).init();
+    }
+
+    // Log build information
+    tracing::info!("Iron Borders v{}", borders_core::build_info::VERSION);
+    tracing::info!("Git: {} | Built: {}", borders_core::build_info::git_commit_short(), borders_core::build_info::BUILD_TIME);
+    tracing::info!("© 2025 Ryan Walters. All Rights Reserved.");
+
+    // Initialize telemetry
+    tokio::runtime::Runtime::new().unwrap().block_on(async {
+        borders_core::telemetry::init(borders_core::telemetry::TelemetryConfig::default()).await;
+        borders_core::telemetry::track_session_start().await;
+    });
+    tracing::info!("Telemetry initialized");
+
+    run();
+}

crates/borders-desktop/src/plugin.rs

@@ -0,0 +1,176 @@
+//! Tauri-Bevy integration plugin
+//!
+//! This module provides the main integration between Tauri and Bevy, handling
+//! the main application loop and event bridging.
+
+use borders_core::app::{App, Plugin, Update};
+use borders_core::time::Time;
+use std::cell::RefCell;
+use std::rc::Rc;
+use std::sync::{Arc, Mutex};
+use std::time::Duration;
+use tauri::{Manager, RunEvent};
+
+#[cfg(not(target_arch = "wasm32"))]
+use std::time::Instant;
+#[cfg(target_arch = "wasm32")]
+use web_time::Instant;
+
+use crate::render_bridge::{TauriRenderBridgeTransport, cache_leaderboard_snapshot_system};
+
+const TARGET_FPS: f64 = 60.0;
+
+pub fn generate_tauri_context() -> tauri::Context {
+    tauri::generate_context!()
+}
+
+fn setup_tauri_integration(app: &mut App, tauri_app: &tauri::AppHandle, shared_render_state: Arc<Mutex<Option<borders_core::ui::protocol::RenderInit>>>, shared_leaderboard_state: Arc<Mutex<Option<borders_core::ui::protocol::LeaderboardSnapshot>>>) {
+    tracing::debug!("Setup tauri integration");
+
+    // Register state for render bridge commands
+    tauri_app.manage(Arc::new(Mutex::new(None::<borders_core::ui::protocol::CameraStateUpdate>)));
+    tauri_app.manage(Arc::new(Mutex::new(None::<borders_core::networking::GameView>)));
+
+    // InputState - shared between Tauri commands and ECS systems
+    let input_state_shared = Arc::new(Mutex::new(borders_core::ui::input::InputState::new()));
+    tauri_app.manage(input_state_shared.clone());
+    app.insert_non_send_resource(input_state_shared);
+
+    // Register shared state with Tauri (for get_game_state command)
+    tauri_app.manage(shared_render_state.clone());
+    tauri_app.manage(shared_leaderboard_state.clone());
+
+    // Get the message queue from the transport (already added as plugin)
+    let transport = app.world().get_resource::<borders_core::ui::RenderBridge<TauriRenderBridgeTransport>>().expect("RenderBridge should be added by plugin");
+    let message_queue = transport.transport.inbound_messages();
+    tauri_app.manage(message_queue);
+
+    // Store shared states in world
+    app.insert_non_send_resource(shared_leaderboard_state);
+}
+
+pub struct TauriPlugin {
+    setup: Box<dyn Fn() -> tauri::App + Send + Sync>,
+}
+
+impl TauriPlugin {
+    pub fn new<F>(setup: F) -> Self
+    where
+        F: Fn() -> tauri::App + Send + Sync + 'static,
+    {
+        Self { setup: Box::new(setup) }
+    }
+}
+
+impl TauriPlugin {
+    pub fn build_and_run(self, mut app: App) -> ! {
+        let tauri_app = (self.setup)();
+
+        // Create shared state for game state recovery
+        let shared_render_state = Arc::new(Mutex::new(None::<borders_core::ui::protocol::RenderInit>));
+        let shared_leaderboard_state = Arc::new(Mutex::new(None::<borders_core::ui::protocol::LeaderboardSnapshot>));
+
+        // Create transport for Tauri frontend (handles both render and UI communication)
+        let transport = TauriRenderBridgeTransport::new(tauri_app.handle().clone(), shared_render_state.clone());
+
+        // Add the render bridge plugin to handle all frontend communication
+        borders_core::ui::FrontendPlugin::new(transport).build(&mut app);
+
+        // Set up Tauri integration directly (no startup system needed)
+        setup_tauri_integration(&mut app, tauri_app.handle(), shared_render_state, shared_leaderboard_state);
+
+        // Add the leaderboard caching system
+        app.add_systems(Update, cache_leaderboard_snapshot_system);
+
+        // Run the app
+        run_tauri_app(app, tauri_app);
+        std::process::exit(0)
+    }
+}
+
+pub fn run_tauri_app(app: App, tauri_app: tauri::App) {
+    let app_rc = Rc::new(RefCell::new(app));
+    let mut tauri_app = tauri_app;
+    let mut is_initialized = false;
+    let mut last_frame_time = Instant::now();
+
+    let target_frame_duration = Duration::from_secs_f64(1.0 / TARGET_FPS);
+
+    loop {
+        let frame_start = Instant::now();
+
+        #[allow(deprecated)]
+        tauri_app.run_iteration(move |_app_handle, event: RunEvent| {
+            match event {
+                tauri::RunEvent::Ready => {
+                    // Event acknowledged, actual setup happens below
+                }
+                tauri::RunEvent::ExitRequested { .. } => {
+                    // Track session end and flush analytics before exit
+                    if borders_core::telemetry::client().is_some() {
+                        tracing::debug!("ExitRequested: tracking session end and flushing analytics");
+
+                        // Create a minimal runtime for blocking operations
+                        let runtime = tokio::runtime::Builder::new_current_thread().enable_time().enable_io().build().expect("Failed to create tokio runtime for flush");
+
+                        runtime.block_on(async {
+                            // Track session end event
+                            borders_core::telemetry::track_session_end().await;
+
+                            // Flush all pending events (the batch-triggered send is now synchronous)
+                            if let Some(client) = borders_core::telemetry::client() {
+                                let timeout = std::time::Duration::from_millis(500);
+                                match tokio::time::timeout(timeout, client.flush()).await {
+                                    Ok(_) => {
+                                        tracing::debug!("Analytics flushed successfully before exit")
+                                    }
+                                    Err(_) => {
+                                        tracing::warn!("Analytics flush timed out after 500ms")
+                                    }
+                                }
+                            }
+                        });
+                    }
+                }
+                _ => (),
+            }
+        });
+
+        if tauri_app.webview_windows().is_empty() {
+            tauri_app.cleanup_before_exit();
+            break;
+        }
+
+        // Initialize game plugin on first iteration after Tauri is ready
+        if !is_initialized {
+            let mut app = app_rc.borrow_mut();
+
+            // Add core game plugin
+            borders_core::GamePlugin::new(borders_core::plugin::NetworkMode::Local).build(&mut app);
+
+            app.run_startup();
+            app.finish();
+            app.cleanup();
+
+            is_initialized = true;
+            last_frame_time = Instant::now(); // Reset timer after initialization
+            tracing::info!("Game initialized");
+        }
+
+        // Update time resource with delta from PREVIOUS frame
+        let mut app = app_rc.borrow_mut();
+        let delta = frame_start.duration_since(last_frame_time);
+        if let Some(mut time) = app.world_mut().get_resource_mut::<Time>() {
+            time.update(delta);
+        }
+
+        app.update();
+
+        let frame_duration = frame_start.elapsed();
+        if frame_duration < target_frame_duration {
+            std::thread::sleep(target_frame_duration - frame_duration);
+        }
+
+        last_frame_time = frame_start;
+    }
+}

crates/borders-desktop/src/render_bridge.rs

@@ -0,0 +1,162 @@
+//! Tauri-specific frontend transport and command handlers
+//!
+//! This module provides the Tauri implementation of FrontendTransport,
+//! along with Tauri command handlers for input events, camera updates, and
+//! state recovery.
+
+use std::collections::VecDeque;
+use std::sync::{Arc, Mutex};
+
+use bevy_ecs::message::MessageReader;
+use bevy_ecs::system::NonSend;
+use borders_core::networking::GameView;
+use borders_core::ui::FrontendTransport;
+use borders_core::ui::protocol::{BackendMessage, CameraStateUpdate, FrontendMessage, LeaderboardSnapshot, MapQuery, MapQueryResponse, RenderInit, RenderInputEvent, TerrainType};
+use serde::{Deserialize, Serialize};
+use tauri::{AppHandle, Emitter};
+use tracing::trace;
+
+/// Tauri-specific frontend transport using Tauri events
+#[derive(Clone)]
+pub struct TauriRenderBridgeTransport {
+    app_handle: AppHandle,
+    /// Shared state for RenderInit (accessible from Tauri commands)
+    shared_render_state: Arc<Mutex<Option<RenderInit>>>,
+    /// Inbound messages from the frontend
+    inbound_messages: Arc<Mutex<VecDeque<FrontendMessage>>>,
+}
+
+impl TauriRenderBridgeTransport {
+    pub fn new(app_handle: AppHandle, shared_render_state: Arc<Mutex<Option<RenderInit>>>) -> Self {
+        Self { app_handle, shared_render_state, inbound_messages: Arc::new(Mutex::new(VecDeque::new())) }
+    }
+
+    /// Get a reference to the inbound messages queue (for Tauri command handler)
+    pub fn inbound_messages(&self) -> Arc<Mutex<VecDeque<FrontendMessage>>> {
+        self.inbound_messages.clone()
+    }
+}
+
+impl FrontendTransport for TauriRenderBridgeTransport {
+    fn send_backend_message(&self, message: &BackendMessage) -> Result<(), String> {
+        // Cache RenderInit for state recovery on reload
+        if let BackendMessage::RenderInit(render_init) = message
+            && let Ok(mut state) = self.shared_render_state.lock()
+        {
+            *state = Some(render_init.clone());
+        }
+
+        self.app_handle.emit("backend:message", message).map_err(|e| format!("Failed to emit backend message: {}", e))
+    }
+
+    fn send_binary_delta(&self, data: Vec<u8>) -> Result<(), String> {
+        self.app_handle.emit("render:pixel_stream", &data).map_err(|e| format!("Failed to emit pixel stream: {}", e))
+    }
+
+    fn try_recv_frontend_message(&self) -> Option<FrontendMessage> {
+        if let Ok(mut messages) = self.inbound_messages.lock() { messages.pop_front() } else { None }
+    }
+}
+
+/// Tauri command handler for receiving frontend messages
+#[tauri::command]
+pub fn send_frontend_message(message: FrontendMessage, bridge: tauri::State<Arc<Mutex<VecDeque<FrontendMessage>>>>) -> Result<(), String> {
+    tracing::info!("Frontend sent message: {:?}", message);
+    if let Ok(mut messages) = bridge.lock() {
+        messages.push_back(message);
+        tracing::debug!("Message queued, queue size: {}", messages.len());
+        Ok(())
+    } else {
+        tracing::error!("Failed to acquire lock on message queue");
+        Err("Failed to acquire lock on message queue".to_string())
+    }
+}
+
+/// Handle input events from the frontend
+#[tauri::command]
+pub fn handle_render_input(event: RenderInputEvent, input_state: tauri::State<Arc<Mutex<borders_core::ui::input::InputState>>>) -> Result<(), String> {
+    let mut state = input_state.lock().map_err(|e| format!("Failed to lock input state: {}", e))?;
+
+    // TODO: Get actual map width from GameView or TerrainData
+    let map_width = 2560; // Placeholder
+
+    borders_core::ui::handle_render_input(&event, &mut state, map_width)
+}
+
+/// Handle camera state updates from the frontend
+#[tauri::command]
+pub fn handle_camera_update(update: CameraStateUpdate, bridge: tauri::State<Arc<Mutex<Option<CameraStateUpdate>>>>) -> Result<(), String> {
+    let mut state = bridge.lock().map_err(|e| format!("Failed to lock camera state: {}", e))?;
+
+    borders_core::ui::handle_camera_update(update, &mut state)
+}
+
+/// Handle map queries from the frontend
+#[tauri::command]
+pub fn handle_map_query(query: MapQuery, game_view: tauri::State<Arc<Mutex<Option<GameView>>>>) -> Result<MapQueryResponse, String> {
+    let view = game_view.lock().map_err(|e| format!("Failed to lock game view: {}", e))?;
+
+    let Some(ref view) = *view else {
+        return Err("Game view not available".to_string());
+    };
+
+    match query {
+        MapQuery::GetOwnerAt { x: _, y: _ } => {
+            // This query is not used with Pixi.js frontend - frontend sends tile indices directly
+            Ok(MapQueryResponse::Owner { owner_id: 0, tile_index: None })
+        }
+        MapQuery::GetTileInfo { tile_index } => {
+            let index = tile_index as usize;
+            let owner_id = view.get_owner(index);
+
+            // TODO: Get actual terrain and troop data
+            Ok(MapQueryResponse::TileInfo {
+                tile_index,
+                owner_id,
+                terrain: TerrainType::Land, // Placeholder
+                troops: 0,                  // Placeholder
+            })
+        }
+        MapQuery::FindPlayerTerritory { player_id } => {
+            let tile_index = view.find_tile_owned_by(player_id).map(|i| i as u32);
+            Ok(MapQueryResponse::PlayerTerritory { tile_index })
+        }
+        MapQuery::ScreenToTile { screen_x: _, screen_y: _ } => {
+            // This would need camera state to work properly
+            Ok(MapQueryResponse::TileIndex { index: None })
+        }
+    }
+}
+
+/// Combined state for recovery after reload
+#[derive(Debug, Clone, Serialize, Deserialize)]
+pub struct GameStateRecovery {
+    pub render_init: Option<RenderInit>,
+    pub leaderboard_snapshot: Option<LeaderboardSnapshot>,
+}
+
+/// Get current game state for frontend recovery after reload
+#[tauri::command]
+pub fn get_game_state(render_state: tauri::State<Arc<Mutex<Option<RenderInit>>>>, leaderboard_state: tauri::State<Arc<Mutex<Option<LeaderboardSnapshot>>>>) -> Result<GameStateRecovery, String> {
+    let render_init = render_state.lock().map_err(|e| format!("Failed to lock render state: {}", e))?.clone();
+
+    let leaderboard_snapshot = leaderboard_state.lock().map_err(|e| format!("Failed to lock leaderboard state: {}", e))?.clone();
+
+    Ok(GameStateRecovery { render_init, leaderboard_snapshot })
+}
+
+/// System to cache leaderboard snapshots for state recovery
+pub fn cache_leaderboard_snapshot_system(mut events: MessageReader<BackendMessage>, shared_leaderboard_state: Option<NonSend<Arc<Mutex<Option<LeaderboardSnapshot>>>>>) {
+    let Some(shared_state) = shared_leaderboard_state else {
+        return;
+    };
+
+    for event in events.read() {
+        if let BackendMessage::LeaderboardSnapshot(snapshot) = event
+            && let Ok(mut state) = shared_state.lock()
+        {
+            *state = Some(snapshot.clone());
+            trace!("Cached leaderboard snapshot for state recovery");
+        }
+    }
+}

crates/borders-desktop/tauri.conf.json

@@ -0,0 +1,40 @@
+{
+  "$schema": "https://schema.tauri.app/config/2",
+  "productName": "iron-borders",
+  "version": "0.1.0",
+  "identifier": "com.xevion.iron-borders",
+  "build": {
+    "beforeDevCommand": "pnpm dev",
+    "devUrl": "http://localhost:1420",
+    "beforeBuildCommand": "pnpm build:desktop",
+    "frontendDist": "../../frontend/dist/client"
+  },
+  "app": {
+    "windows": [
+      {
+        "title": "Iron Borders",
+        "width": 1280,
+        "height": 720
+      }
+    ],
+    "security": {
+      "csp": null
+    }
+  },
+  "plugins": {
+    "process": {
+      "all": true
+    }
+  },
+  "bundle": {
+    "active": true,
+    "targets": ["appimage", "deb", "rpm", "dmg"],
+    "icon": [
+      "icons/32x32.png",
+      "icons/128x128.png",
+      "icons/128x128@2x.png",
+      "icons/icon.icns",
+      "icons/icon.ico"
+    ]
+  }
+}