feat(backend): add GET /api/diagnostics/config route + test

- Returns sanitized config: productId, serviceName, port, nodeEnv, dbProvider, telemetryEnabled, featureFlagsEnabled
- Integration test validates response shape

backend/src/diagnostics.test.ts

@@ -3,6 +3,8 @@ import Fastify from 'fastify';
 import type { FastifyInstance } from 'fastify';
 import { getAllFlags } from './lib/feature-flags.js';
 import { getBufferedEvents, flushEvents } from './lib/telemetry.js';
+import { config } from './lib/config.js';
+import { PRODUCT_ID } from './lib/product-config.js';
 
 let app: FastifyInstance;
 
@@ -11,6 +13,15 @@ beforeAll(async () => {
   app.get('/api/diagnostics/flags', async () => getAllFlags());
   app.get('/api/diagnostics/telemetry', async () => ({ events: getBufferedEvents() }));
   app.post('/api/diagnostics/telemetry/flush', async () => ({ flushed: flushEvents().length }));
+  app.get('/api/diagnostics/config', async () => ({
+    productId: PRODUCT_ID,
+    serviceName: config.SERVICE_NAME,
+    port: config.PORT,
+    nodeEnv: config.NODE_ENV,
+    dbProvider: config.DB_PROVIDER,
+    telemetryEnabled: config.TELEMETRY_ENABLED,
+    featureFlagsEnabled: config.FEATURE_FLAGS_ENABLED,
+  }));
   await app.ready();
 });
 
@@ -42,4 +53,17 @@ describe('diagnostics routes', () => {
     expect(body).toHaveProperty('flushed');
     expect(typeof body.flushed).toBe('number');
   });
+
+  it('GET /api/diagnostics/config returns sanitized config', async () => {
+    const res = await app.inject({ method: 'GET', url: '/api/diagnostics/config' });
+    expect(res.statusCode).toBe(200);
+    const body = res.json();
+    expect(body).toHaveProperty('productId');
+    expect(body).toHaveProperty('serviceName');
+    expect(body).toHaveProperty('port');
+    expect(body).toHaveProperty('nodeEnv');
+    expect(body).toHaveProperty('dbProvider');
+    expect(typeof body.telemetryEnabled).toBe('boolean');
+    expect(typeof body.featureFlagsEnabled).toBe('boolean');
+  });
 });

backend/src/server.ts

@@ -12,7 +12,7 @@ import { initDatastore } from './lib/datastore.js';
 import { config } from './lib/config.js';
 import { getAllFlags } from './lib/feature-flags.js';
 import { getBufferedEvents, flushEvents } from './lib/telemetry.js';
-import { DISPLAY_NAME } from './lib/product-config.js';
+import { DISPLAY_NAME, PRODUCT_ID } from './lib/product-config.js';
 import type { JwtPayload } from './lib/request-context.js';
 
 const jwtSecret = new TextEncoder().encode(config.JWT_SECRET);
@@ -59,5 +59,14 @@ await registerApiPlugin(workspaceRoutes);
 app.get('/api/diagnostics/flags', async () => getAllFlags());
 app.get('/api/diagnostics/telemetry', async () => ({ events: getBufferedEvents() }));
 app.post('/api/diagnostics/telemetry/flush', async () => ({ flushed: flushEvents().length }));
+app.get('/api/diagnostics/config', async () => ({
+  productId: PRODUCT_ID,
+  serviceName: config.SERVICE_NAME,
+  port: config.PORT,
+  nodeEnv: config.NODE_ENV,
+  dbProvider: config.DB_PROVIDER,
+  telemetryEnabled: config.TELEMETRY_ENABLED,
+  featureFlagsEnabled: config.FEATURE_FLAGS_ENABLED,
+}));
 
 await startService(app, { port: config.PORT, host: config.HOST });