quill: add incident postmortem template with example

wizard-work/quill/incident-postmortem-template.md

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+# Incident Postmortem — [Service Name]
+
+## Metadata
+- Incident ID: INC-2026-001
+- Severity: SEV-2
+- Date: 2026-10-24
+- Duration: 42 minutes
+- Author: quill
+
+## Summary
+A dependency upgrade introduced a breaking change in the authentication flow, causing a 42-minute outage affecting 18% of user sessions.
+
+## Timeline (all times UTC)
+- 14:03 — v2.4.1 deployed to prod
+- 14:05 — PagerDuty alert: auth failure rate > 5%
+- 14:07 — on-call confirmed spike, began rollback
+- 14:22 — rollback completed to v2.4.0
+- 14:35 — verification passed, all-clear sent
+- 14:45 — postmortem scheduled
+
+## Root Cause
+`auth-client` v3.1.0 changed the token refresh endpoint path from `/oauth/token` to `/v2/oauth/token`. The deploy updated the dependency but did not update the hardcoded path. All refresh attempts 404'd until rollback.
+
+## Blast Radius
+- 18% of active sessions affected
+- ~12,000 failed login/refresh attempts
+- 3 downstream services degraded (notifications, recommendations, search indexing)
+
+## Resolution
+Rollback to v2.4.0 restored service. Post-rollback, we patched the path constant and re-deployed v2.4.2 with the fix plus a regression test.
+
+## Action Items
+1. Add contract test for auth endpoint paths (owner: @alex, due: 2026-10-31)
+2. Pin auth-client in CI until path test is green (owner: @quill, due: 2026-10-27)
+3. Add dependency-change alert in deploy pipeline (owner: @bot-crew, due: 2026-11-03)
+
+## Lessons Learned
+- Do not silently bump major versions in patch deploys.
+- Path constants should be discovered, not hardcoded.
+- Rollback runbook needs a <5-min verification gate.