docs(orchestrator): Add Sprint Completion Protocol + archive M6-Fixes

Add sprint archival instructions so completed tasks.md files are
retained in docs/tasks/ for post-mortem reference. Includes recovery
behavior when an orchestrator finds no active tasks.md.

Archive M6-AgentOrchestration-Fixes: 88/90 done, 2 deferred.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

docs/claude/orchestrator.md

@@ -524,6 +524,71 @@ QA automation generates report files in `docs/reports/qa-automation/pending/`. C
 
 ---
 
+## Sprint Completion Protocol
+
+When all tasks in `docs/tasks.md` are `done` (or triaged as `deferred`), archive the sprint artifacts before stopping. This preserves them for post-mortems, variance calibration, and historical reference.
+
+### Archive Steps
+
+1. **Create archive directory** (if it doesn't exist):
+
+   ```bash
+   mkdir -p docs/tasks/
+   ```
+
+2. **Move tasks.md to archive:**
+
+   ```bash
+   mv docs/tasks.md docs/tasks/{milestone-name}-tasks.md
+   ```
+
+   Example: `docs/tasks/M6-AgentOrchestration-Fixes-tasks.md`
+
+3. **Move learnings to archive:**
+
+   ```bash
+   mv docs/orchestrator-learnings.json docs/tasks/{milestone-name}-learnings.json
+   ```
+
+4. **Commit the archive:**
+
+   ```bash
+   git add docs/tasks/
+   git rm docs/tasks.md docs/orchestrator-learnings.json 2>/dev/null || true
+   git commit -m "chore(orchestrator): Archive {milestone-name} sprint artifacts
+
+   {completed}/{total} tasks completed, {deferred} deferred.
+   Archived to docs/tasks/ for post-mortem reference."
+   git push
+   ```
+
+5. **Run final retrospective** — review variance patterns and propose updates to estimation heuristics.
+
+### Recovery
+
+If an orchestrator starts and `docs/tasks.md` does not exist, check `docs/tasks/` for the most recent archive:
+
+```bash
+ls -t docs/tasks/*-tasks.md 2>/dev/null | head -1
+```
+
+If found, this may indicate another session archived the file. The orchestrator should:
+
+1. Report what it found in `docs/tasks/`
+2. Ask whether to resume from the archived file or bootstrap fresh
+3. If resuming: copy the archive back to `docs/tasks.md` and continue
+
+### Retention Policy
+
+Keep all archived sprints indefinitely. They are small text files and valuable for:
+
+- Post-mortem analysis
+- Estimation variance calibration across milestones
+- Understanding what was deferred and why
+- Onboarding new orchestrators to project history
+
+---
+
 ## Kickstart Message Format
 
 ```markdown