apps/server/src/integrations/static/static.module.spec.ts

@@ -1,3 +1,8 @@
+import * as fs from 'node:fs';
+import * as os from 'node:os';
+import { join } from 'node:path';
+import Fastify, { FastifyInstance } from 'fastify';
+import fastifyStatic from '@fastify/static';
 import { resolveStaticAssetHeaders } from './static.module';
 
 // Unit tests for the static-asset cache classifier extracted from the
@@ -33,3 +38,69 @@ describe('resolveStaticAssetHeaders', () => {
     expect(headers['vary']).toBe('Accept-Encoding');
   });
 });
+
+// Integration test proving the ACTUAL response header emitted by @fastify/static
+// with the exact registration options StaticModule uses. This is the regression
+// guard for #452: without `cacheControl: false`, @fastify/static writes its own
+// `Cache-Control: public, max-age=0` AFTER the setHeaders callback, overwriting
+// the immutable header — the /assets/ assertion below would then fail.
+describe('static.module @fastify/static registration (integration)', () => {
+  let app: FastifyInstance;
+  let tmpDir: string;
+
+  beforeAll(async () => {
+    tmpDir = fs.mkdtempSync(join(os.tmpdir(), 'static-module-spec-'));
+    fs.mkdirSync(join(tmpDir, 'assets'), { recursive: true });
+    fs.mkdirSync(join(tmpDir, 'locales'), { recursive: true });
+    fs.writeFileSync(
+      join(tmpDir, 'assets', 'index-a1b2c3.js'),
+      'console.log(1);',
+    );
+    fs.writeFileSync(join(tmpDir, 'locales', 'en.json'), '{"hello":"world"}');
+
+    app = Fastify();
+    // Mirror StaticModule.onModuleInit's registration options exactly.
+    await app.register(fastifyStatic, {
+      root: tmpDir,
+      wildcard: false,
+      preCompressed: true,
+      cacheControl: false,
+      setHeaders: (res, filePath) => {
+        for (const [name, value] of Object.entries(
+          resolveStaticAssetHeaders(filePath),
+        )) {
+          res.setHeader(name, value);
+        }
+      },
+    });
+    await app.ready();
+  });
+
+  afterAll(async () => {
+    await app.close();
+    fs.rmSync(tmpDir, { recursive: true, force: true });
+  });
+
+  it('serves a hashed /assets/ file with an immutable, 1-year cache-control', async () => {
+    const res = await app.inject({
+      method: 'GET',
+      url: '/assets/index-a1b2c3.js',
+    });
+    expect(res.statusCode).toBe(200);
+    const cacheControl = res.headers['cache-control'];
+    expect(cacheControl).toContain('immutable');
+    expect(cacheControl).toContain('max-age=31536000');
+  });
+
+  it('serves a non-hashed /locales/ file WITHOUT an immutable cache-control', async () => {
+    const res = await app.inject({ method: 'GET', url: '/locales/en.json' });
+    expect(res.statusCode).toBe(200);
+    // resolveStaticAssetHeaders sets no cache-control here and cacheControl:false
+    // stops @fastify/static from adding one, so the browser revalidates by
+    // etag/last-modified — either an absent header or one without `immutable`.
+    const cacheControl = res.headers['cache-control'];
+    if (cacheControl !== undefined) {
+      expect(cacheControl).not.toContain('immutable');
+    }
+  });
+});

apps/server/src/integrations/static/static.module.ts

@@ -115,6 +115,11 @@ export class StaticModule implements OnModuleInit {
         // Serve the build-time .br/.gz neighbour when the client accepts it
         // (see vite-plugin-compression2 in apps/client/vite.config.ts).
         preCompressed: true,
+        // @fastify/static's default cacheControl:true writes its own
+        // Cache-Control (from maxAge, default 0) AFTER the setHeaders callback,
+        // silently overwriting the immutable header that resolveStaticAssetHeaders
+        // sets — disable it so setHeaders/resolveStaticAssetHeaders own the header.
+        cacheControl: false,
         setHeaders: (res, filePath) => {
           for (const [name, value] of Object.entries(
             resolveStaticAssetHeaders(filePath),