--- a/server/media-cache.test.js
+++ b/server/media-cache.test.js
@@ -10,6 +10,8 @@
 process.env.DB_PATH = join(root, 'test.db');
 const dbmod = await import('./db.js');
 const { createMediaCache, validateMedia, MediaSkip, HIGH, LOW, OPT_REV } = await import('./media-cache.js');
+const { initP2pSchema } = await import('./p2p-db.js');
+const { sha256File } = await import('./hash.js');
 
 const fx = (name) => join(root, name);
 const ff = (...args) => {
@@ -26,6 +28,7 @@
 
 beforeAll(async () => {
   await dbmod.initDb();
+  await initP2pSchema(); // adds media_cache.sha256
   // 10 s 640x360 H.264 + AAC — the shape of a good cached copy.
   ff('-f', 'lavfi', '-i', 'testsrc=size=640x360:rate=30:duration=10', '-f', 'lavfi', '-i', 'sine=frequency=440:duration=10',
      '-c:v', 'libx264', '-preset', 'ultrafast', '-pix_fmt', 'yuv420p', '-c:a', 'aac', '-shortest', fx('good.mp4'));
@@ -102,6 +105,7 @@
     download: async (id, out) => { calls.push(id); await sleep(30); copyFileSync(fx(state.fixture), out); return out; },
     transcode: { enabled: false },
     freeBytes: () => 100 * 1024 ** 3,
+    backfillDelayMs: -1,
     ...opts,
   });
   return { cache, dir, calls, state };
@@ -110,6 +114,35 @@
   for (const r of await dbmod.listMedia()) await dbmod.deleteMedia(r.video_id);
 }
 
+describe('content hashes (P2P cids)', () => {
+  test('a promoted copy stores the sha256 of its mp4 and reports it once', async () => {
+    await clearDb();
+    const seen = [];
+    const { cache, dir } = makeCache({ onReady: (i) => { seen.push(i); } });
+    await cache.init();
+    const row = await cache.ensureCached('hashAAAAAA1', { priority: HIGH });
+    const want = await sha256File(join(dir, `hashAAAAAA1.${row.gen}.mp4`));
+    expect((await dbmod.getMedia('hashAAAAAA1')).sha256).toBe(want);
+    expect(await until(() => seen.length === 1)).toBe(true);
+    expect(seen[0]).toMatchObject({ id: 'hashAAAAAA1', gen: row.gen, sha256: want, vcodec: 'h264' });
+    expect(seen[0].meta.title).toBe('T hashAAAAAA1');
+  });
+
+  test('backfill hashes ready copies that have no sha256 yet', async () => {
+    await clearDb();
+    const seen = [];
+    const { cache } = makeCache({ onReady: (i) => { seen.push(i); } });
+    await cache.init();
+    await cache.ensureCached('hashAAAAAA2', { priority: HIGH });
+    await dbmod.upsertMedia('hashAAAAAA2', { sha256: null });
+    seen.length = 0;
+    expect(await cache.backfillHashes()).toBe(1);
+    expect((await dbmod.getMedia('hashAAAAAA2')).sha256).toMatch(/^[0-9a-f]{64}$/);
+    expect(await until(() => seen.length === 1)).toBe(true);
+    expect(await cache.backfillHashes()).toBe(0); // nothing left
+  });
+});
+
 describe('media cache jobs', () => {
   test('fetches once, dedupes concurrent requests, then serves from disk', async () => {
     await clearDb();