Update CLAUDE.md with reasoning trace parsing fix documentation

- Document the reasoning trace parsing fix added 2025-08-07
- Explain the problem, solution, and benefits
- Update existing reasoning trace section to note well-formed requirement
- Add technical details about the fix

CLAUDE.md

@@ -52,6 +52,8 @@ The application now supports displaying reasoning traces from models like NuMark
 **Implementation Details:**
 - New `reasoning-parser.js` module handles detection and parsing of reasoning traces
 - Supports multiple reasoning formats (`<think>`, `<thinking>`, `<reasoning>` tags)
+- **Important:** Only well-formed traces with both opening AND closing tags are parsed
+- Malformed traces (missing closing tags) are displayed as plain text
 - Formats numbered steps from reasoning content for structured display
 - Caches parsed reasoning to avoid reprocessing
 - Exports include optional reasoning trace content
@@ -329,4 +331,29 @@ The application now displays model processing information when available:
 **Implementation Notes:**
 - The model info panel only appears when `inference_info` column exists
 - Supports datasets processed with UV scripts via HF Jobs
-- Gracefully handles datasets without model metadata
+- Gracefully handles datasets without model metadata
+
+### Reasoning Trace Parsing Fix (Added 2025-08-07)
+
+Fixed an issue where reasoning traces with incomplete or malformed XML tags would cause parsing errors:
+
+**Problem:**
+- Some model outputs contained opening `<think>` tags without closing `</think>` tags
+- This appeared to be truncated or malformed model output
+- The parser would attempt to parse these incomplete traces, causing confusion
+
+**Solution:**
+- Updated `detectReasoningTrace()` to require BOTH opening and closing tags
+- Added console warnings when incomplete traces are detected
+- Malformed traces are now displayed as plain text instead of being parsed
+
+**Benefits:**
+- Cleaner handling of incomplete model outputs
+- No confusing partial reasoning panels for malformed content
+- Maintains full functionality for well-formed reasoning traces
+- Helpful console warnings for debugging
+
+**Technical Details:**
+- File: `js/reasoning-parser.js`
+- Only traces with complete XML tags (`<think>...</think>`, `<thinking>...</thinking>`, etc.) are parsed
+- Incomplete traces log: "Incomplete reasoning trace detected - missing closing tags"