chore: complete v1.0 Analytics & Monitoring milestone

Archive milestone artifacts (roadmap, requirements, audit, phase directories)
to .planning/milestones/. Evolve PROJECT.md with validated requirements and
decision outcomes. Create MILESTONES.md and RETROSPECTIVE.md.

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

.planning/milestones/v1.0-phases/02-backend-services/02-02-SUMMARY.md

@@ -0,0 +1,122 @@
+---
+phase: 02-backend-services
+plan: 02
+subsystem: infra
+tags: [health-probes, document-ai, anthropic, firebase-auth, postgres, vitest, nodemailer]
+
+# Dependency graph
+requires:
+  - phase: 01-data-foundation
+    provides: HealthCheckModel.create() for persistence
+  - phase: 02-backend-services
+    plan: 01
+    provides: Schema and model layer for service_health_checks table
+
+provides:
+  - healthProbeService with 4 real API probers (document_ai, llm_api, supabase, firebase_auth)
+  - ProbeResult interface exported for use by health endpoint
+  - runAllProbes orchestrator with fault-tolerant probe isolation
+  - nodemailer installed (needed by Plan 03 alert notifications)
+
+affects: [02-backend-services, 02-03-PLAN]
+
+# Tech tracking
+tech-stack:
+  added: [nodemailer@8.0.1, @types/nodemailer]
+  patterns:
+    - Promise.allSettled for fault-tolerant concurrent probe orchestration
+    - firebase-admin verifyIdToken probe distinguishes expected vs unexpected errors
+    - Direct PostgreSQL pool (getPostgresPool) for Supabase probe, not PostgREST
+    - LLM probe uses cheapest model (claude-haiku-4-5) with max_tokens 5
+
+key-files:
+  created:
+    - backend/src/services/healthProbeService.ts
+    - backend/src/__tests__/unit/healthProbeService.test.ts
+  modified:
+    - backend/package.json (nodemailer + @types/nodemailer added)
+
+key-decisions:
+  - "LLM probe uses claude-haiku-4-5 with max_tokens 5 (cheapest available, prevents expensive accidental probes)"
+  - "Supabase probe uses getPostgresPool().query('SELECT 1') not PostgREST client (bypasses caching/middleware)"
+  - "Firebase Auth probe uses verifyIdToken('invalid-token') — always throws, distinguished by error message content"
+  - "Promise.allSettled chosen over Promise.all to guarantee all probes run even if one throws outside try/catch"
+  - "HealthCheckModel.create failure per probe is swallowed with logger.error — probe results still returned to caller"
+
+patterns-established:
+  - "Probe pattern: record start time, try real API call, compute latency, return ProbeResult with status/latency_ms/error_message"
+  - "Firebase SDK probe: verifyIdToken always throws; 'argument'/'INVALID'/'Decoding' in message = SDK alive = healthy"
+  - "429 rate limit errors = degraded (not down) — service is alive but throttling"
+  - "vi.mock with inline vi.fn() in factory — no outer variable references (Vitest hoisting TDZ safe)"
+
+requirements-completed: [HLTH-02, HLTH-04]
+
+# Metrics
+duration: 18min
+completed: 2026-02-24
+---
+
+# Phase 02 Plan 02: Health Probe Service Summary
+
+**Four real authenticated API probers (Document AI, LLM claude-haiku-4-5, Supabase pg pool, Firebase Auth) with fault-tolerant orchestrator and Supabase persistence via HealthCheckModel**
+
+## Performance
+
+- **Duration:** 18 min
+- **Started:** 2026-02-24T14:05:00Z
+- **Completed:** 2026-02-24T14:23:55Z
+- **Tasks:** 2
+- **Files modified:** 4
+
+## Accomplishments
+
+- Created `healthProbeService.ts` with 4 individual probers each making real authenticated API calls
+- Implemented `runAllProbes` orchestrator using `Promise.allSettled` for fault isolation (one probe failure never blocks others)
+- Each probe result persisted to Supabase via `HealthCheckModel.create()` after completion
+- 9 unit tests covering all probers, fault tolerance, 429 degraded handling, Supabase pool verification, and Firebase error discrimination
+- Installed nodemailer (needed by Plan 03 alert notifications) to avoid package.json conflicts in parallel execution
+
+## Task Commits
+
+Each task was committed atomically:
+
+1. **Task 1: Install nodemailer and create healthProbeService** - `4129826` (feat)
+2. **Task 2: Create healthProbeService unit tests** - `a8ba884` (test)
+
+**Plan metadata:** (docs commit — created below)
+
+## Files Created/Modified
+
+- `backend/src/services/healthProbeService.ts` - Health probe orchestrator with ProbeResult interface and 4 individual probers
+- `backend/src/__tests__/unit/healthProbeService.test.ts` - 9 unit tests covering all probers and orchestrator
+- `backend/package.json` - nodemailer + @types/nodemailer added
+
+## Decisions Made
+
+- LLM probe uses `claude-haiku-4-5` with `max_tokens: 5` — cheapest Anthropic model prevents accidental expensive probe calls
+- Supabase probe uses `getPostgresPool().query('SELECT 1')` — bypasses PostgREST middleware/caching, tests actual DB connectivity
+- Firebase Auth probe strategy: `verifyIdToken('invalid-token-probe-check')` always throws; error message containing 'argument', 'INVALID', or 'Decoding' = SDK functioning = 'healthy'
+- `Promise.allSettled` over `Promise.all` — guarantees all 4 probes run even if one rejects outside its own try/catch
+- Per-probe persistence failure is swallowed (logger.error only) so probe results are still returned to caller
+
+## Deviations from Plan
+
+None - plan executed exactly as written.
+
+## Issues Encountered
+
+None — all probes compiled and tested cleanly on first implementation.
+
+## User Setup Required
+
+None - no external service configuration required beyond what's already in .env.
+
+## Next Phase Readiness
+
+- `healthProbeService.runAllProbes()` is ready to be called by the health scheduler (Plan 03)
+- `nodemailer` is installed and ready for Plan 03 alert notification service
+- `ProbeResult` interface exported and ready for use in health status API endpoints
+
+---
+*Phase: 02-backend-services*
+*Completed: 2026-02-24*