feat(observability): structured logs, W3C trace IDs, Sentry hooks (#18)

- TS: pino + pino-http; every HTTP request log includes traceId from
  W3C traceparent header (generated if absent); forwarded to ml/serving
  on all /score, /generate, /reward, and /api/ml proxy calls
- Python: structlog JSON; FastAPI middleware binds trace_id via
  contextvars so every log line within a request carries it
- Sentry: optional SENTRY_DSN init in both runtimes (no-op if unset)
- Replace all console.* calls across services/api with pino logger
- Update tests to spy on logger instead of console

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

services/api/src/index.ts

@@ -1,7 +1,10 @@
 import 'dotenv/config';
+import { logger } from './logger.js';
 import express from 'express';
+import { pinoHttp } from 'pino-http';
 import cookieParser from 'cookie-parser';
 import cors from 'cors';
+import { tracingMiddleware } from './middleware/tracing.js';
 import { config } from './config.js';
 import { db, runMigrations } from './db/index.js';
 import { tipScores, tipFeedback } from './db/schema.js';
@@ -26,13 +29,11 @@ import { registerProfileSubscriptions } from './profile/subscriber.js';
 await mkdir(dirname(config.DATABASE_PATH), { recursive: true });
 runMigrations();
 
-// Keep the API alive on stray async faults (e.g. a single bad admin route)
-// rather than dropping the whole process.
 process.on('unhandledRejection', (reason) => {
-  console.error('[api] unhandledRejection', reason);
+  logger.error({ err: reason }, 'unhandledRejection');
 });
 process.on('uncaughtException', (err) => {
-  console.error('[api] uncaughtException', err);
+  logger.fatal({ err }, 'uncaughtException');
 });
 
 const app = express();
@@ -43,6 +44,15 @@ app.use(
     credentials: true,
   }),
 );
+app.use(tracingMiddleware);
+app.use(
+  pinoHttp({
+    logger,
+    genReqId: (req) => req.traceId,
+    customProps: (req) => ({ traceId: req.traceId }),
+    autoLogging: { ignore: (req) => req.url === '/health' },
+  }),
+);
 app.use(express.json());
 app.use(cookieParser());
 app.use(sessionMiddleware);
@@ -56,16 +66,13 @@ app.use('/api/user', userRouter);
 app.use('/api/push', pushRouter);
 app.use('/api/admin', adminRouter);
 
-// Proxy ml/serving endpoints through the API (admin-only).
-// Allows admin UI to call /api/ml/stats/:userId, /api/ml/features/:userId
-// without needing direct access to the ml/serving port.
 app.use('/api/ml', requireAuth as any, requireAdmin as any, async (req: Request, res: Response) => {
   const mlUrl = config.ML_SERVING_URL;
   const target = `${mlUrl}${req.path}`;
   try {
     const upstream = await fetch(target, {
       method: req.method,
-      headers: { 'Content-Type': 'application/json' },
+      headers: { 'Content-Type': 'application/json', traceparent: req.traceparent },
       body: req.method !== 'GET' ? JSON.stringify(req.body) : undefined,
       signal: AbortSignal.timeout(5000),
     });
@@ -82,7 +89,7 @@ async function purgeExpiredData() {
     await db.delete(tipScores).where(lt(tipScores.servedAt, cutoff));
     await db.delete(tipFeedback).where(lt(tipFeedback.createdAt, cutoff));
   } catch (err: any) {
-    console.error(`[purge] retention cleanup failed: ${err.message}`);
+    logger.error({ err }, 'retention cleanup failed');
   }
 }
 
@@ -90,7 +97,7 @@ purgeExpiredData();
 setInterval(purgeExpiredData, 24 * 60 * 60 * 1000);
 
 app.listen(config.PORT, () => {
-  console.log(`oO API listening on http://localhost:${config.PORT}`);
+  logger.info({ port: config.PORT }, 'oO API listening');
 });
 
 if (config.NATS_URL) {