handoff-update

Update an existing handoff document with this session's progress. ## Step 1: Resolve the Handoff File Determine which file to update, in this priority order: 1. If `$ARGUMENTS[0]` was provided, use it as the file path. 2. If this session was started via `/handoff:resume`, look in conversation history for the argument that was passed to it. 3. If neither is found, fall back to creating a new file: `claudedocs/handoffs/handoff_YYYYMMDD_HHMMSS.md`. Inform the user that no existing handoff was found. ## Step 2: Read the Existing File Read the resolved file completely. Parse all sections as the baseline for the merge. ## Step 3: Apply Section Merge Rules Rewrite the file with updated content using these merge rules: | Section | Rule | Notes | |---------|------|-------| | **Task** | Keep original | Update only if scope fundamentally changed | | **Scope** | Keep or refine | Narrow it if new understanding emerged | | **Files** | Merge | Add new files touched in this session. Keep originals. Use `path:line` format | | **Discoveries** | Append | Add new findings below existing list. Never remove prior discoveries | | **Work Done** | **Append only** | Add new completed items below existing list. Never remove entries. Include commit hashes | | **Status** | **Replace** | Write the current state: what is done now, what remains, test status | | **Next Steps** | **Replace** | Write the updated actionable checklist | | **Code** | Update | Replace with the most relevant snippets from t...