# 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.