fix(web): cache static assets

.changeset/calm-files-cache.md

@@ -0,0 +1,5 @@
+---
+"@moonshot-ai/kimi-code": patch
+---
+
+Cache web assets between page loads while revalidating the application shell.

packages/kap-server/src/routes/webAssets.ts

@@ -56,10 +56,18 @@ async function serveWebAsset(
 
   return reply
     .type(mimeType(filePath))
+    .header('Cache-Control', cacheControl(assetsDir, filePath))
     .header('Content-Length', String(fileInfo.size))
     .send(createReadStream(filePath));
 }
 
+function cacheControl(assetsDir: string, filePath: string): string {
+  const assetsRoot = resolve(assetsDir, 'assets');
+  return filePath.startsWith(`${assetsRoot}${sep}`)
+    ? 'public, max-age=31536000, immutable'
+    : 'no-cache';
+}
+
 async function resolveStaticFile(
   assetsDir: string,
   pathname: string,

packages/kap-server/test/webAssets.test.ts

@@ -0,0 +1,52 @@
+import { mkdir, mkdtemp, rm, writeFile } from 'node:fs/promises';
+import { tmpdir } from 'node:os';
+import { join } from 'node:path';
+
+import Fastify, { type FastifyInstance } from 'fastify';
+import { afterEach, beforeEach, describe, expect, it } from 'vitest';
+
+import { registerWebAssetRoutes } from '../src/routes/webAssets';
+
+describe('web asset cache policy', () => {
+  let app: FastifyInstance;
+  let assetsDir: string;
+
+  beforeEach(async () => {
+    assetsDir = await mkdtemp(join(tmpdir(), 'kimi-web-assets-'));
+    await mkdir(join(assetsDir, 'assets'));
+    await writeFile(join(assetsDir, 'index.html'), '<main>Kimi</main>');
+    await writeFile(join(assetsDir, 'assets', 'index-Dy7xs5tu.js'), 'export {};');
+
+    app = Fastify();
+    await registerWebAssetRoutes(app, assetsDir);
+    await app.ready();
+  });
+
+  afterEach(async () => {
+    await app.close();
+    await rm(assetsDir, { recursive: true, force: true });
+  });
+
+  it('caches fingerprinted Vite assets as immutable', async () => {
+    const response = await app.inject({
+      method: 'GET',
+      url: '/assets/index-Dy7xs5tu.js',
+    });
+
+    expect(response.statusCode).toBe(200);
+    expect(response.headers['cache-control']).toBe(
+      'public, max-age=31536000, immutable',
+    );
+  });
+
+  it.each(['/', '/index.html', '/sessions/current', '/assets/preview'])(
+    'revalidates HTML responses for %s',
+    async (url) => {
+      const response = await app.inject({ method: 'GET', url });
+
+      expect(response.statusCode).toBe(200);
+      expect(response.headers['cache-control']).toBe('no-cache');
+      expect(response.headers['content-type']).toBe('text/html; charset=utf-8');
+    },
+  );
+});