music: officer-music sidecar + /api/music streaming proxy

Adds an officer-music sidecar that owns an audio-streaming HTTP server, and a
thin authenticating proxy on the platform. All processing (path resolution,
byte-range streaming, ffprobe duration) is in the sidecar; the platform only
authenticates and forwards.

App-facing contract (handoff):
  GET /api/music/stream?path=<home-relative path>&token=<jwt>
    - auth via userMiddleware (Bearer or ?token= for media elements)
    - 200 full / 206 on Range, with Accept-Ranges, Content-Length,
      Content-Range, Content-Type, and X-Audio-Duration (seconds, ffprobe)
    - path resolved within HOME_DIR, traversal-guarded (400); 404 if missing
  Purpose: stream + seek without pre-downloading the whole file — the app can
  read X-Audio-Duration instead of scanning for VBR duration.

Pieces:
- sidecar/music/{index.ts,stream-audio.ts}: Bun.serve on a random port, /stream
  + /health, duration cached by path+mtime; reports its port via a new
  music:server sidecar event on connect.
- api/music/{sidecar-server.ts,router.ts}: capture the port; reverse-proxy
  /api/music/* → sidecar, streaming status + headers through.
- protocol.ts music:server event; hono.ts mounts /api/music; ecosystem adds
  officer-music.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

src/servers/sidecar/music/index.ts

@@ -0,0 +1,92 @@
+import type { SidecarCommand, SidecarEvent } from '../protocol';
+import { createSidecarConnector } from '../connect';
+import { streamAudioFile } from './stream-audio';
+
+// The music sidecar (officer-music). Same philosophy as the other officer-* sidecars: a singleton
+// process that registers with the API server. It OWNS an audio-streaming HTTP server (all path
+// resolution + streaming + ffprobe duration happens here); the platform API is just a thin proxy that
+// authenticates and forwards to us. The server listens on a random loopback port, reported to the API
+// on connect so it can route `/api/music/*` here.
+
+const API_URL = process.env.API_URL ?? `ws://127.0.0.1:${process.env.PORT ?? '5000'}`;
+
+// ── Audio-streaming HTTP server ──
+
+/** Grab an ephemeral free port by briefly binding one and releasing it. */
+function getFreePort(): number {
+  const probe = Bun.serve({ port: 0, hostname: '127.0.0.1', fetch: () => new Response('') });
+  const port = probe.port;
+  probe.stop(true);
+  if (port == null) throw new Error('failed to acquire a free port');
+  return port;
+}
+
+const port = getFreePort();
+
+const server = Bun.serve({
+  port,
+  hostname: '127.0.0.1',
+  async fetch(req) {
+    const url = new URL(req.url);
+    if (url.pathname === '/health') return new Response('ok');
+    if (url.pathname === '/stream') {
+      const path = url.searchParams.get('path');
+      if (!path) return new Response('path is required', { status: 400 });
+      return streamAudioFile(path, req.headers.get('range'));
+    }
+    return new Response('Not found', { status: 404 });
+  },
+});
+
+console.log(`[music] audio server listening on http://127.0.0.1:${port}`);
+
+// ── Command handlers ──
+
+type ReplyFn = (msg: SidecarEvent) => void;
+
+function handleCommand(cmd: SidecarCommand, reply: ReplyFn) {
+  switch (cmd.type) {
+    case 'ping':
+      reply({ type: 'pong', id: cmd.id });
+      break;
+
+    default:
+      reply({
+        type: 'error',
+        id: (cmd as SidecarCommand).id,
+        error: `Unknown command type: ${(cmd as Record<string, unknown>).type}`,
+      });
+  }
+}
+
+// ── Connect to API server ──
+
+const connection = createSidecarConnector({
+  apiUrl: `${API_URL}/api/sidecar/register`,
+  name: 'music',
+  capabilities: ['music'],
+  onCommand(cmd, reply) {
+    handleCommand(cmd as SidecarCommand, reply as ReplyFn);
+  },
+  onConnected() {
+    // Tell the API where our audio server is listening, so it can proxy /api/music/* here.
+    connection.send({ type: 'music:server', port });
+    console.log(`[music] reported audio server port ${port} to API`);
+  },
+});
+
+// ── Graceful shutdown ──
+
+function shutdown(signal: string) {
+  console.log(`[music] ${signal} received, shutting down...`);
+  try {
+    server.stop(true);
+  } catch {
+    /* already stopped */
+  }
+  connection.destroy();
+  process.exit(0);
+}
+
+process.on('SIGTERM', () => shutdown('SIGTERM'));
+process.on('SIGINT', () => shutdown('SIGINT'));

src/servers/sidecar/music/stream-audio.ts

@@ -0,0 +1,97 @@
+import { stat } from 'node:fs/promises';
+import { resolve, sep } from 'node:path';
+import { homedir } from 'node:os';
+
+// All processing lives here (the platform is just a proxy). Files live under the owner's home — single
+// super user, so HOME_DIR. Paths from the app are home-relative (e.g. "Music/Artist/Album/track.mp3"),
+// exactly like file-browser /raw.
+const ROOT_DIR = process.env.HOME_DIR ?? homedir();
+
+const CONTENT_TYPES: Record<string, string> = {
+  mp3: 'audio/mpeg',
+  m4a: 'audio/mp4',
+  mp4: 'audio/mp4',
+  aac: 'audio/aac',
+  flac: 'audio/flac',
+  wav: 'audio/wav',
+  ogg: 'audio/ogg',
+  opus: 'audio/opus',
+  wma: 'audio/x-ms-wma',
+};
+
+// Probe duration once per file (keyed by absolute path + mtime) — the player makes many range requests
+// per track, and we don't want to shell out to ffprobe on each one.
+const durationCache = new Map<string, number>();
+
+async function probeDuration(absPath: string, mtimeMs: number): Promise<number | undefined> {
+  const key = `${absPath}:${mtimeMs}`;
+  const cached = durationCache.get(key);
+  if (cached !== undefined) return cached;
+  try {
+    const proc = Bun.spawn(
+      ['ffprobe', '-v', 'error', '-show_entries', 'format=duration', '-of', 'default=noprint_wrappers=1:nokey=1', absPath],
+      { stdout: 'pipe', stderr: 'ignore' },
+    );
+    const out = (await new Response(proc.stdout).text()).trim();
+    await proc.exited;
+    const d = parseFloat(out);
+    if (Number.isFinite(d) && d > 0) {
+      durationCache.set(key, d);
+      return d;
+    }
+  } catch {
+    /* ffprobe missing or failed — no duration header */
+  }
+  return undefined;
+}
+
+/** Resolve a home-relative path within ROOT_DIR; null if it escapes (traversal). */
+function resolveWithinRoot(relPath: string): string | null {
+  const clean = relPath.replace(/^\/+/, '');
+  const abs = resolve(ROOT_DIR, clean);
+  if (abs !== ROOT_DIR && !abs.startsWith(ROOT_DIR + sep)) return null;
+  return abs;
+}
+
+/** Serve an audio file with byte-range support + an X-Audio-Duration header (ffprobe-derived). */
+export async function streamAudioFile(relPath: string, rangeHeader: string | null): Promise<Response> {
+  const absPath = resolveWithinRoot(relPath);
+  if (!absPath) return new Response('Invalid path', { status: 400 });
+
+  let s;
+  try {
+    s = await stat(absPath);
+  } catch {
+    return new Response('Not found', { status: 404 });
+  }
+  if (!s.isFile()) return new Response('Not a file', { status: 404 });
+
+  const total = s.size;
+  const ext = absPath.slice(absPath.lastIndexOf('.') + 1).toLowerCase();
+  const contentType = CONTENT_TYPES[ext] ?? 'application/octet-stream';
+  const duration = await probeDuration(absPath, s.mtimeMs);
+  const file = Bun.file(absPath);
+
+  const baseHeaders: Record<string, string> = {
+    'Content-Type': contentType,
+    'Accept-Ranges': 'bytes',
+    ...(duration ? { 'X-Audio-Duration': String(duration) } : {}),
+  };
+
+  if (rangeHeader) {
+    const m = rangeHeader.match(/bytes=(\d*)-(\d*)/);
+    if (m) {
+      const start = m[1] ? parseInt(m[1], 10) : 0;
+      const end = m[2] ? parseInt(m[2], 10) : total - 1;
+      if (Number.isNaN(start) || start < 0 || end >= total || start > end) {
+        return new Response('Invalid range', { status: 416, headers: { 'Content-Range': `bytes */${total}` } });
+      }
+      return new Response(file.slice(start, end + 1), {
+        status: 206,
+        headers: { ...baseHeaders, 'Content-Range': `bytes ${start}-${end}/${total}`, 'Content-Length': String(end - start + 1) },
+      });
+    }
+  }
+
+  return new Response(file, { status: 200, headers: { ...baseHeaders, 'Content-Length': String(total) } });
+}