feat(api): add Prometheus metrics and OpenTelemetry instrumentation for HTTP, auth, classifications, and diagnoses

apps/api/src/routes/auth.ts

@@ -16,6 +16,7 @@ import {
   verifyPassword,
 } from '../lib/auth';
 import { env } from '../config/env';
+import { authCounter } from '../lib/telemetry';
 
 function normalizeEmail(email: unknown) {
   return typeof email === 'string' ? email.trim().toLowerCase() : '';
@@ -63,6 +64,8 @@ export const authRoutes = new Elysia({ prefix: '/api/v1/auth' })
       const token = await createSession(user.id);
       set.headers['Set-Cookie'] = createSessionCookie(token);
 
+      authCounter.labels('register', 'true').inc();
+
       return {
         user: {
           id: user.id,
@@ -90,12 +93,15 @@ export const authRoutes = new Elysia({ prefix: '/api/v1/auth' })
       const user = rows[0];
 
       if (!user?.passwordHash || !(await verifyPassword(req!.password!, user.passwordHash))) {
+        authCounter.labels('login', 'false').inc();
         return badRequest('Invalid email or password');
       }
 
       const token = await createSession(user.id);
       set.headers['Set-Cookie'] = createSessionCookie(token);
 
+      authCounter.labels('login', 'true').inc();
+
       return {
         user: {
           id: user.id,

apps/api/src/routes/classifications.ts

@@ -16,6 +16,7 @@ import { desc, eq } from 'drizzle-orm';
 import { classifyImage } from '../lib/image-model';
 import { uploadImageToStorage } from '../lib/uploader-client';
 import { toDisease } from '../lib/disease-mappers';
+import { classificationCounter } from '../lib/telemetry';
 
 function toImageClassificationRecord(row: {
   id: string;
@@ -141,6 +142,8 @@ export const classificationRoutes = new Elysia({ prefix: '/api/v1' })
         );
       }
 
+      classificationCounter.labels(classificationResult.predictedDiseaseSlug).inc();
+
       const db = createDbClient();
       let diseaseRow;
       try {

apps/api/src/routes/diagnoses.ts

@@ -9,6 +9,7 @@ import { getCurrentUser } from '../lib/auth';
 import { classifyImage } from '../lib/image-model';
 import { uploadImageToStorage } from '../lib/uploader-client';
 import { env } from '../config/env';
+import { diagnosisCounter } from '../lib/telemetry';
 
 interface ReviewRow {
   reviewId: string | null;
@@ -222,6 +223,9 @@ export const diagnosisRoutes = new Elysia({ prefix: '/api/v1' })
 
       const record = await loadDiagnosisRecord(inserted[0].id, user.id, false);
       if (!record) return serviceUnavailable('Database unavailable');
+
+      diagnosisCounter.labels(record.predictedDiseaseSlug ?? 'unknown').inc();
+
       return record;
     } catch (error) {
       const inserted = await db
@@ -240,6 +244,9 @@ export const diagnosisRoutes = new Elysia({ prefix: '/api/v1' })
 
       const record = await loadDiagnosisRecord(inserted[0].id, user.id, false);
       if (!record) return serviceUnavailable('Database unavailable');
+
+      diagnosisCounter.labels('failed').inc();
+
       return record;
     }
   })

apps/api/src/routes/metrics.ts

@@ -0,0 +1,10 @@
+import { Elysia } from 'elysia';
+import { getMetrics, getMetricsContentType } from '../lib/telemetry';
+
+export const metricsRoutes = new Elysia()
+  .get('/metrics', async () => {
+    const body = await getMetrics();
+    return new Response(body, {
+      headers: { 'Content-Type': getMetricsContentType() },
+    });
+  });