Feed Generator Service - Metrics/Logging

[Ashex]

Service needs structured logging, Prometheus metrics, robust graceful shutdown, request-ID tracing, and a soak test to confirm no FD leaks or unbounded memory growth.

Metrics to expose (/metrics)

Metric	Labels
feedgen_requests_total	endpoint, status
feedgen_request_duration_seconds	endpoint
feedgen_subscriptions_open	kind="service"|"actor"
feedgen_subscription_reconnects_total	kind, did (optional)
feedgen_index_posts_total	—
feedgen_blob_cache_hits_total / _misses_total	—
feedgen_boundary_cache_hits_total / _misses_total	—

To-do

• Add src/logger.ts — pino logger with Stratos service conventions
• Add request-ID middleware (src/middleware/request-id.ts): accept X-Request-Id or generate UUID; attach to AsyncLocalStorage
• Instrument all request handlers to log {requestId, viewerDid?, endpoint, durationMs, status}
• Add src/metrics.ts — Prometheus-format counter/histogram helpers; register all metrics above
• Expose /metrics endpoint
• Add src/lifecycle/shutdown.ts — SIGTERM/SIGINT handler: stop accepting connections → drain in-flight (15 s timeout) → flush actor cursors → close DB
• Enrich /health to return {ok, version, serviceStreamConnected, actorPoolSize}
• Add panic handler: catch unhandled promise rejections + exceptions; log and exit with code 1
• Add tests/shutdown.test.ts and tests/metrics.test.ts
• Soak test (can be a manual step documented in PR): 50 req/s against in-memory data for 5 min; record RSS and FD count before/after

Acceptance criteria

• Every completed request log line includes requestId, viewerDid (where available), and durationMs
• /metrics output passes promtool check metrics or equivalent programmatic validation (test)
• SIGTERM: open requests complete (up to 15 s), actor cursors flushed, DB closed cleanly (integration test)
• /health reflects actual subscription state (serviceStreamConnected, actorPoolSize)
• Handler-level error produces HTTP 500 + logged error; process does not exit (test)
• Soak test shows RSS growth < 50 MB and zero FD leak over 5 min