fix(reference): Fix line attribution accuracy and add Claude Code model extraction #7
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… model extraction The reference implementation had two issues affecting trace accuracy: 1. Line Attribution: When processing edits with context lines (common in Claude Code's Edit tool), the entire new_string was attributed to AI, including unchanged surrounding lines. This produced inflated attribution ranges. 2. Model Identification: Claude Code does not include the model identifier in hook payloads. Traces were created with missing model_id, making it impossible to distinguish which model produced the code. Changes: - Add diffToFindChangedLines() to compute actual changed lines by comparing old_string and new_string, excluding context lines from attribution - Add extractModelFromTranscript() to parse Claude Code's JSONL transcript files and extract the model identifier from message entries - Add resolveModel() helper to transparently handle model resolution for both Cursor (direct payload) and Claude Code (transcript extraction) - Update PostToolUse, SessionStart, and SessionEnd handlers to use the new model resolution logic
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Summary
This PR fixes two correctness issues in the reference implementation affecting Claude Code trace accuracy:
model_idProblem Details
Issue 1: Line Attribution
Claude Code's
Edittool includes context lines in bothold_stringandnew_string. The previous implementation attributed the entirenew_string, incorrectly claiming ownership of unchanged lines.Before: Adding 1 line →
ranges: [{start_line: 1, end_line: 3}]After: Adding 1 line →
ranges: [{start_line: 2, end_line: 2}]Issue 2: Model Identification
Unlike Cursor, Claude Code does not include
modelin hook payloads. The model must be extracted from the transcript JSONL file atentry.message.model.Solution
trace-store.ts
diffToFindChangedLines()- Compares old/new strings to identify only changed linesextractModelFromTranscript()- Reads model from transcript tail (4KB initial read, doubles if needed)trace-hook.ts
resolveModel()- Transparently resolves model from payload (Cursor) or transcript (Claude Code)PostToolUse,SessionStart,SessionEndhandlersTest Results
Tested with alternating Cursor and Claude Code edits in a sample repository:
All traces correctly captured:
Backward Compatibility
afterFileEditunchanged (uses explicit ranges from payload)old_stringandnew_stringare present