fix(anime): strip disguised HLS segments and report real playback errors

Some hosts prepend a fake image header (a real 1x1 PNG) to every HLS
segment; ffmpeg probes the segment as a picture and mpv drops back to
idle with no window while the browser claims the episode is playing.

- Route bridge-served m3u8 streams through a local strip proxy that
  scans each segment for the first genuine MPEG-TS packet run and drops
  the junk in front of it; playlists get absolute origins rewritten so
  segment requests come back through the proxy. Non-TS bodies pass
  through untouched.
- Only report ok from playEpisode once mpv configures a video output;
  an end-file with reason error surfaces mpv's own message (e.g. "no
  audio or video data played") in the browser status bar instead of
  "Playing". New end-file event plumbed through the mpv IPC client.

src/anime-bridge/stream-strip-proxy.test.ts

@@ -0,0 +1,165 @@
+import test from 'node:test';
+import assert from 'node:assert/strict';
+import http from 'node:http';
+import type { AddressInfo } from 'node:net';
+import {
+  findTsSyncOffset,
+  rewritePlaylistOrigins,
+  startStreamStripProxy,
+  TS_PACKET_LENGTH,
+} from './stream-strip-proxy';
+
+/** A valid MPEG-TS payload: 0x47 sync byte every 188 bytes. */
+function makeTsPackets(count: number): Buffer {
+  const data = Buffer.alloc(count * TS_PACKET_LENGTH, 0x11);
+  for (let i = 0; i < count; i++) data[i * TS_PACKET_LENGTH] = 0x47;
+  return data;
+}
+
+/** The disguise seen in the wild: a real PNG header glued before the TS data. */
+const PNG_HEADER = Buffer.from([
+  0x89, 0x50, 0x4e, 0x47, 0x0d, 0x0a, 0x1a, 0x0a, 0x00, 0x00, 0x00, 0x0d, 0x49, 0x48, 0x44, 0x52,
+]);
+
+test('findTsSyncOffset returns 0 for clean TS data', () => {
+  assert.equal(findTsSyncOffset(makeTsPackets(6)), 0);
+});
+
+test('findTsSyncOffset finds TS data behind a PNG prefix', () => {
+  const disguised = Buffer.concat([PNG_HEADER, makeTsPackets(6)]);
+  assert.equal(findTsSyncOffset(disguised), PNG_HEADER.length);
+});
+
+test('findTsSyncOffset ignores a lone sync byte in the junk prefix', () => {
+  const junk = Buffer.alloc(64, 0x00);
+  junk[10] = 0x47; // decoy: no packet run follows it
+  const disguised = Buffer.concat([junk, makeTsPackets(6)]);
+  assert.equal(findTsSyncOffset(disguised), junk.length);
+});
+
+test('findTsSyncOffset returns null when no TS run exists', () => {
+  assert.equal(findTsSyncOffset(Buffer.alloc(4096, 0x42)), null);
+});
+
+test('findTsSyncOffset returns null when the run starts past the scan limit', () => {
+  const disguised = Buffer.concat([Buffer.alloc(600, 0x00), makeTsPackets(6)]);
+  assert.equal(findTsSyncOffset(disguised, 500), null);
+});
+
+test('rewritePlaylistOrigins swaps absolute upstream URLs and keeps relative lines', () => {
+  const body = [
+    '#EXTM3U',
+    '#EXTINF:6.006,',
+    '/video/aaa.ts',
+    '#EXTINF:4.463,',
+    'http://127.0.0.1:41569/video/bbb.ts',
+  ].join('\n');
+  const rewritten = rewritePlaylistOrigins(body, 'http://127.0.0.1:41569', 'http://127.0.0.1:9999');
+  assert.ok(rewritten.includes('http://127.0.0.1:9999/video/bbb.ts'));
+  assert.ok(rewritten.includes('\n/video/aaa.ts\n'));
+  assert.ok(!rewritten.includes('41569'));
+});
+
+/* ---------- proxy end-to-end ---------- */
+
+type Route = { status: number; contentType: string; body: Buffer };
+
+async function withProxy(
+  routes: Record<string, Route>,
+  run: (proxyOrigin: string, upstreamOrigin: string) => Promise<void>,
+): Promise<void> {
+  const upstream = http.createServer((req, res) => {
+    const route = routes[req.url ?? ''];
+    if (!route) {
+      res.writeHead(404).end('missing');
+      return;
+    }
+    res.writeHead(route.status, { 'content-type': route.contentType });
+    res.end(route.body);
+  });
+  await new Promise<void>((resolve) => upstream.listen(0, '127.0.0.1', resolve));
+  const upstreamOrigin = `http://127.0.0.1:${(upstream.address() as AddressInfo).port}`;
+
+  const proxy = await startStreamStripProxy({ upstreamOrigin: () => upstreamOrigin });
+  try {
+    await run(proxy.origin, upstreamOrigin);
+  } finally {
+    await proxy.close();
+    await new Promise<void>((resolve) => upstream.close(() => resolve()));
+  }
+}
+
+async function fetchBytes(url: string): Promise<{ status: number; body: Buffer }> {
+  const response = await fetch(url);
+  return { status: response.status, body: Buffer.from(await response.arrayBuffer()) };
+}
+
+test('proxy strips the PNG disguise off a segment', async () => {
+  const ts = makeTsPackets(8);
+  const disguised = Buffer.concat([PNG_HEADER, ts]);
+  await withProxy(
+    { '/video/seg.ts': { status: 200, contentType: 'video/mp2t', body: disguised } },
+    async (origin) => {
+      const { status, body } = await fetchBytes(`${origin}/video/seg.ts`);
+      assert.equal(status, 200);
+      assert.deepEqual(body, ts);
+    },
+  );
+});
+
+test('proxy passes a clean segment through unchanged', async () => {
+  const ts = makeTsPackets(8);
+  await withProxy(
+    { '/video/seg.ts': { status: 200, contentType: 'video/mp2t', body: ts } },
+    async (origin) => {
+      const { body } = await fetchBytes(`${origin}/video/seg.ts`);
+      assert.deepEqual(body, ts);
+    },
+  );
+});
+
+test('proxy leaves non-TS bodies alone', async () => {
+  const vtt = Buffer.from('WEBVTT\n\n00:00.000 --> 00:01.000\nhello\n');
+  await withProxy(
+    { '/video/sub.vtt': { status: 200, contentType: 'text/vtt', body: vtt } },
+    async (origin) => {
+      const { body } = await fetchBytes(`${origin}/video/sub.vtt`);
+      assert.deepEqual(body, vtt);
+    },
+  );
+});
+
+test('proxy rewrites absolute upstream playlist entries to its own origin', async () => {
+  const upstream = http.createServer((req, res) => {
+    const origin = `http://127.0.0.1:${(upstream.address() as AddressInfo).port}`;
+    if (req.url === '/video/list.m3u8') {
+      res.writeHead(200, { 'content-type': 'application/vnd.apple.mpegurl' });
+      res.end(`#EXTM3U\n#EXTINF:6,\n${origin}/video/abs.ts\n`);
+      return;
+    }
+    res.writeHead(404).end();
+  });
+  await new Promise<void>((resolve) => upstream.listen(0, '127.0.0.1', resolve));
+  const upstreamOrigin = `http://127.0.0.1:${(upstream.address() as AddressInfo).port}`;
+  const proxy = await startStreamStripProxy({ upstreamOrigin: () => upstreamOrigin });
+  try {
+    const { body } = await fetchBytes(`${proxy.origin}/video/list.m3u8`);
+    const text = body.toString('utf8');
+    assert.ok(text.includes(`${proxy.origin}/video/abs.ts`));
+    assert.ok(!text.includes(upstreamOrigin));
+  } finally {
+    await proxy.close();
+    await new Promise<void>((resolve) => upstream.close(() => resolve()));
+  }
+});
+
+test('proxy forwards error statuses without touching the body', async () => {
+  await withProxy(
+    { '/video/gone.ts': { status: 404, contentType: 'text/plain', body: Buffer.from('nope') } },
+    async (origin) => {
+      const { status, body } = await fetchBytes(`${origin}/video/gone.ts`);
+      assert.equal(status, 404);
+      assert.equal(body.toString('utf8'), 'nope');
+    },
+  );
+});