feat(json): enhance error context with debug mode detailed reporting

Improve JSON parsing error messages with build-specific behavior:
- Debug builds: Show full parent object context and type mismatch details
- Release builds: Keep minimal snippets to avoid log spam

Add comprehensive test coverage for error handling and path parsing.

src/banner/json.rs

@@ -1,10 +1,14 @@
 //! JSON parsing utilities for the Banner API client.
 
 use anyhow::Result;
-use serde_json;
+use serde_json::{self, Value};
 
 /// Attempt to parse JSON and, on failure, include a contextual snippet of the
-/// line where the error occurred. This prevents dumping huge JSON bodies to logs.
+/// line where the error occurred.
+///
+/// In debug builds, this provides detailed context including the full JSON object
+/// containing the error and type mismatch information. In release builds, it shows
+/// a minimal snippet to prevent dumping huge JSON bodies to production logs.
 pub fn parse_json_with_context<T: serde::de::DeserializeOwned>(body: &str) -> Result<T> {
     let jd = &mut serde_json::Deserializer::from_str(body);
     match serde_path_to_error::deserialize(jd) {
@@ -12,27 +16,244 @@ pub fn parse_json_with_context<T: serde::de::DeserializeOwned>(body: &str) -> Re
         Err(err) => {
             let inner_err = err.inner();
             let (line, column) = (inner_err.line(), inner_err.column());
-            let snippet = build_error_snippet(body, line, column, 20);
             let path = err.path().to_string();
 
             let msg = inner_err.to_string();
             let loc = format!(" at line {line} column {column}");
             let msg_without_loc = msg.strip_suffix(&loc).unwrap_or(&msg).to_string();
 
-            let mut final_err = String::new();
-            if !path.is_empty() && path != "." {
-                final_err.push_str(&format!("for path '{}' ", path));
-            }
-            final_err.push_str(&format!(
-                "({msg_without_loc}) at line {line} column {column}"
-            ));
-            final_err.push_str(&format!("\n{snippet}"));
+            // Build error message differently for debug vs release builds
+            let final_err = if cfg!(debug_assertions) {
+                // Debug mode: provide detailed context
+                let type_info = parse_type_mismatch(&msg_without_loc);
+                let context = extract_json_object_at_path(body, err.path(), line, column);
+
+                let mut err_msg = String::new();
+                if !path.is_empty() && path != "." {
+                    err_msg.push_str(&format!("for path '{}'\n", path));
+                }
+                err_msg.push_str(&format!("({}) at line {} column {}\n\n", type_info, line, column));
+                err_msg.push_str(&context);
+
+                err_msg
+            } else {
+                // Release mode: minimal snippet to keep logs concise
+                let snippet = build_error_snippet(body, line, column, 20);
+
+                let mut err_msg = String::new();
+                if !path.is_empty() && path != "." {
+                    err_msg.push_str(&format!("for path '{}' ", path));
+                }
+                err_msg.push_str(&format!(
+                    "({}) at line {} column {}",
+                    msg_without_loc, line, column
+                ));
+                err_msg.push_str(&format!("\n{}", snippet));
+
+                err_msg
+            };
 
             Err(anyhow::anyhow!(final_err))
         }
     }
 }
 
+/// Extract type mismatch information from a serde error message.
+///
+/// Parses error messages like "invalid type: null, expected a string" to extract
+/// the expected and actual types for clearer error reporting.
+///
+/// Returns a formatted string like "(expected a string, got null)" or the original
+/// message if parsing fails.
+fn parse_type_mismatch(error_msg: &str) -> String {
+    // Try to parse "invalid type: X, expected Y" format
+    if let Some(invalid_start) = error_msg.find("invalid type: ") {
+        let after_prefix = &error_msg[invalid_start + "invalid type: ".len()..];
+
+        if let Some(comma_pos) = after_prefix.find(", expected ") {
+            let actual_type = &after_prefix[..comma_pos];
+            let expected_part = &after_prefix[comma_pos + ", expected ".len()..];
+
+            // Clean up expected part (remove " at line X column Y" if present)
+            let expected_type = expected_part
+                .split(" at line ")
+                .next()
+                .unwrap_or(expected_part)
+                .trim();
+
+            return format!("expected {}, got {}", expected_type, actual_type);
+        }
+    }
+
+    // Try to parse "expected X at line Y" format
+    if error_msg.starts_with("expected ") {
+        if let Some(expected_part) = error_msg.split(" at line ").next() {
+            return expected_part.to_string();
+        }
+    }
+
+    // Fallback: return original message without location info
+    error_msg.to_string()
+}
+
+/// Extract and pretty-print the JSON object/array containing the parse error.
+///
+/// This function navigates to the error location using the serde path and extracts
+/// the parent object or array to provide better context for debugging.
+///
+/// # Arguments
+/// * `body` - The raw JSON string
+/// * `path` - The serde path to the error (e.g., "data[0].faculty[0].displayName")
+/// * `line` - Line number of the error (for fallback)
+/// * `column` - Column number of the error (for fallback)
+///
+/// # Returns
+/// A formatted string containing the JSON object with the error, or a fallback snippet
+fn extract_json_object_at_path(
+    body: &str,
+    path: &serde_path_to_error::Path,
+    line: usize,
+    column: usize,
+) -> String {
+    // Try to parse the entire JSON structure
+    let root_value: Value = match serde_json::from_str(body) {
+        Ok(v) => v,
+        Err(_) => {
+            // If we can't parse the JSON at all, fall back to line snippet
+            return build_error_snippet(body, line, column, 20);
+        }
+    };
+
+    // Navigate to the error location using the path
+    let path_str = path.to_string();
+    let segments = parse_path_segments(&path_str);
+
+    let (context_value, context_name) = navigate_to_context(&root_value, &segments);
+
+    // Pretty-print the context value with limited depth to avoid huge output
+    match serde_json::to_string_pretty(&context_value) {
+        Ok(pretty) => {
+            // Limit output to ~50 lines to prevent log spam
+            let lines: Vec<&str> = pretty.lines().collect();
+            let truncated = if lines.len() > 50 {
+                let mut result = lines[..47].join("\n");
+                result.push_str("\n  ... (truncated, ");
+                result.push_str(&(lines.len() - 47).to_string());
+                result.push_str(" more lines)");
+                result
+            } else {
+                pretty
+            };
+
+            format!("{} at '{}':\n{}", context_name, path_str, truncated)
+        }
+        Err(_) => {
+            // Fallback to simple snippet if pretty-print fails
+            build_error_snippet(body, line, column, 20)
+        }
+    }
+}
+
+/// Parse a JSON path string into segments for navigation.
+///
+/// Converts paths like "data[0].faculty[1].displayName" into a sequence of
+/// object keys and array indices.
+fn parse_path_segments(path: &str) -> Vec<PathSegment> {
+    let mut segments = Vec::new();
+    let mut current = String::new();
+    let mut in_bracket = false;
+
+    for ch in path.chars() {
+        match ch {
+            '.' if !in_bracket => {
+                if !current.is_empty() {
+                    segments.push(PathSegment::Key(current.clone()));
+                    current.clear();
+                }
+            }
+            '[' => {
+                if !current.is_empty() {
+                    segments.push(PathSegment::Key(current.clone()));
+                    current.clear();
+                }
+                in_bracket = true;
+            }
+            ']' => {
+                if in_bracket && !current.is_empty() {
+                    if let Ok(index) = current.parse::<usize>() {
+                        segments.push(PathSegment::Index(index));
+                    }
+                    current.clear();
+                }
+                in_bracket = false;
+            }
+            _ => current.push(ch),
+        }
+    }
+
+    if !current.is_empty() {
+        segments.push(PathSegment::Key(current));
+    }
+
+    segments
+}
+
+/// Represents a segment in a JSON path (either an object key or array index).
+#[derive(Debug)]
+enum PathSegment {
+    Key(String),
+    Index(usize),
+}
+
+/// Navigate through a JSON value using path segments and return the appropriate context.
+///
+/// This function walks the JSON structure and returns the parent object/array that
+/// contains the error, providing meaningful context for debugging.
+///
+/// # Returns
+/// A tuple of (context_value, description) where context_value is the JSON to display
+/// and description is a human-readable name for what we're showing.
+fn navigate_to_context<'a>(
+    mut current: &'a Value,
+    segments: &[PathSegment],
+) -> (&'a Value, &'static str) {
+    // If path is empty or just root, return the whole value
+    if segments.is_empty() {
+        return (current, "Root object");
+    }
+
+    // Try to navigate to the parent of the error location
+    // We want to show the containing object/array, not just the failing field
+    let parent_depth = segments.len().saturating_sub(1);
+
+    for (i, segment) in segments.iter().enumerate() {
+        // Stop one level before the end to show the parent context
+        if i >= parent_depth {
+            break;
+        }
+
+        match segment {
+            PathSegment::Key(key) => {
+                if let Some(next) = current.get(key) {
+                    current = next;
+                } else {
+                    // Can't navigate further, return what we have
+                    return (current, "Partial context (navigation stopped)");
+                }
+            }
+            PathSegment::Index(idx) => {
+                if let Some(next) = current.get(idx) {
+                    current = next;
+                } else {
+                    return (current, "Partial context (index out of bounds)");
+                }
+            }
+        }
+    }
+
+    (current, "Object containing error")
+}
+
 fn build_error_snippet(body: &str, line: usize, column: usize, context_len: usize) -> String {
     let target_line = body.lines().nth(line.saturating_sub(1)).unwrap_or("");
     if target_line.is_empty() {
@@ -53,3 +274,139 @@ fn build_error_snippet(body: &str, line: usize, column: usize, context_len: usiz
 
     format!("...{slice}...\n   {indicator}")
 }
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+    use serde::Deserialize;
+
+    #[test]
+    fn test_parse_type_mismatch_invalid_type() {
+        let msg = "invalid type: null, expected a string at line 45 column 29";
+        let result = parse_type_mismatch(msg);
+        assert_eq!(result, "expected a string, got null");
+    }
+
+    #[test]
+    fn test_parse_type_mismatch_expected() {
+        let msg = "expected value at line 1 column 1";
+        let result = parse_type_mismatch(msg);
+        assert_eq!(result, "expected value");
+    }
+
+    #[test]
+    fn test_parse_path_segments_simple() {
+        let segments = parse_path_segments("data.name");
+        assert_eq!(segments.len(), 2);
+        match &segments[0] {
+            PathSegment::Key(k) => assert_eq!(k, "data"),
+            _ => panic!("Expected Key segment"),
+        }
+    }
+
+    #[test]
+    fn test_parse_path_segments_with_array() {
+        let segments = parse_path_segments("data[0].faculty[1].displayName");
+        assert_eq!(segments.len(), 5);
+        match &segments[0] {
+            PathSegment::Key(k) => assert_eq!(k, "data"),
+            _ => panic!("Expected Key segment"),
+        }
+        match &segments[1] {
+            PathSegment::Index(i) => assert_eq!(*i, 0),
+            _ => panic!("Expected Index segment"),
+        }
+    }
+
+    #[test]
+    fn test_parse_json_with_context_null_value() {
+        #[derive(Debug, Deserialize)]
+        struct TestStruct {
+            name: String,
+        }
+
+        let json = r#"{"name": null}"#;
+        let result: Result<TestStruct> = parse_json_with_context(json);
+
+        assert!(result.is_err());
+        let err_msg = result.unwrap_err().to_string();
+
+        // Should contain path info
+        assert!(err_msg.contains("name"));
+
+        // In debug mode, should contain detailed context
+        if cfg!(debug_assertions) {
+            assert!(err_msg.contains("expected"));
+        }
+    }
+
+    #[test]
+    fn test_navigate_to_context() {
+        let json = r#"{"data": [{"faculty": [{"name": "John"}]}]}"#;
+        let value: Value = serde_json::from_str(json).unwrap();
+
+        let segments = parse_path_segments("data[0].faculty[0].name");
+        let (context, _) = navigate_to_context(&value, &segments);
+
+        // Should return the faculty[0] object (parent of 'name')
+        assert!(context.is_object());
+        assert!(context.get("name").is_some());
+    }
+
+    #[test]
+    fn test_realistic_banner_error() {
+        #[derive(Debug, Deserialize)]
+        struct Course {
+            #[allow(dead_code)]
+            #[serde(rename = "courseTitle")]
+            course_title: String,
+            faculty: Vec<Faculty>,
+        }
+
+        #[derive(Debug, Deserialize)]
+        struct Faculty {
+            #[serde(rename = "displayName")]
+            display_name: String,
+            #[allow(dead_code)]
+            email: String,
+        }
+
+        #[derive(Debug, Deserialize)]
+        struct SearchResult {
+            data: Vec<Course>,
+        }
+
+        // Simulate Banner API response with null faculty displayName
+        // This mimics the actual error from SPN subject scrape
+        let json = r#"{
+            "data": [
+                {
+                    "courseTitle": "Spanish Conversation",
+                    "faculty": [
+                        {
+                            "displayName": null,
+                            "email": "instructor@utsa.edu"
+                        }
+                    ]
+                }
+            ]
+        }"#;
+
+        let result: Result<SearchResult> = parse_json_with_context(json);
+        assert!(result.is_err());
+
+        let err_msg = result.unwrap_err().to_string();
+        println!("\n=== Error output in debug mode ===\n{}\n", err_msg);
+
+        // Verify error contains key information
+        assert!(err_msg.contains("data[0].faculty[0].displayName"));
+
+        // In debug mode, should show detailed context
+        if cfg!(debug_assertions) {
+            // Should show type mismatch info
+            assert!(err_msg.contains("expected") && err_msg.contains("got"));
+            // Should show surrounding JSON context with the faculty object
+            assert!(err_msg.contains("email"));
+        }
+    }
+}