- Add _parse_triage_update_marker() parser following existing marker pattern
- Add [TRIAGE_UPDATE] instructions to system prompt with grounding rules
- Add QuestionItem.options support in question parser
- Wire triage extraction into both main and branch-aware chat paths
- Auto-PATCH session: AI only fills null fields (manual edits win)
- Evidence items: AI appends only, never modifies existing
- Return triage_update in ChatMessageResponse for frontend header sync
Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>