feat: LAN Wi-Fi casting to Chromecast via local HTTP relay

Re-serve decrypted fMP4 video over HTTP on the LAN so a Chromecast can
play the stream. The relay runs in the Electron main process — same trust
boundary as downloads and MSE playback.

- cast-relay.js: HTTP server with BoxAccumulator (reassembles WebRTC
  chunks into moof+mdat pairs), ring buffer, backpressure, finish() for
  clean end-of-stream, fixed port range 19550-19553
- cast-chromecast.js: mDNS discovery (bonjour-service) + CASTV2 protocol
  (castv2-client), connect/reload/disconnect lifecycle
- Seek-aware: relay restarts on every seek, Chromecast reloads new URL;
  generation counter prevents stale async errors from killing active
  restarts; landingPlayheadRef suppresses programmatic seeking events
- Device picker in video top bar with scan, device selection, copy-URL
  fallback, and cast status indicator
- IPC bridge (main/preload/platform) for start/push/stop/finish/status/
  discover/chromecastConnect/chromecastReload/chromecastDisconnect
- Phase 3 design doc for DLNA/Smart TV in docs/cast-smart-tv.md

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

1 files changed, 59 insertions, 0 deletions

diff --git a/packages/meshbay-client/src/main.js b/packages/meshbay-client/src/main.js
index f2ec645..45e8462 100644
--- a/packages/meshbay-client/src/main.js
+++ b/packages/meshbay-client/src/main.js
@@ -351,6 +351,11 @@ function createWindow() {
 // renderer parses decrypted content from nodes, which is attacker-controlled
 // input, so it is treated as hostile even though it is our own code.
 
+const CastRelay = require('./cast-relay.js');
+const castRelay = new CastRelay();
+const CastChromecast = require('./cast-chromecast.js');
+const castChromecast = new CastChromecast();
+
 function registerBridge() {
   ipcMain.handle('hub:set', async (_e, base) => {
     const url = String(base || '').trim().replace(/\/+$/, '');
@@ -738,6 +743,60 @@ function registerBridge() {
     _nodePairingCode = code || null;
     return true;
   });
+
+  // ── LAN cast relay ──────────────────────────────────────────────────────
+  //
+  // A local HTTP server that re-serves decrypted fMP4 segments so a
+  // Chromecast or Smart TV on the same Wi-Fi can stream the video. The
+  // renderer feeds it segments via IPC; the relay serves them over HTTP.
+  // Same trust boundary as the MSE player and the download-to-disk path.
+
+  ipcMain.handle('cast:start', async (_e, opts) => {
+    return castRelay.start({
+      codec: opts.codec,
+      initSegment: opts.initSegment ? Buffer.from(opts.initSegment) : null,
+    });
+  });
+
+  ipcMain.handle('cast:push', async (_e, data) => {
+    castRelay.pushSegment(Buffer.from(data));
+    return true;
+  });
+
+  ipcMain.handle('cast:stop', async () => {
+    await castRelay.stop();
+    return true;
+  });
+
+  ipcMain.handle('cast:finish', async () => {
+    castRelay.finish();
+    return true;
+  });
+
+  ipcMain.handle('cast:status', async () => ({
+    active: castRelay.active,
+    url: castRelay.url,
+    chromecast: castChromecast.getStatus(),
+  }));
+
+  // ── Chromecast discovery + control ──────────────────────────────────────
+
+  ipcMain.handle('cast:discover', async () => {
+    return castChromecast.discover();
+  });
+
+  ipcMain.handle('cast:chromecast:connect', async (_e, { deviceId, mediaUrl }) => {
+    return castChromecast.connect(deviceId, mediaUrl);
+  });
+
+  ipcMain.handle('cast:chromecast:reload', async (_e, { mediaUrl }) => {
+    return castChromecast.reload(mediaUrl);
+  });
+
+  ipcMain.handle('cast:chromecast:disconnect', async () => {
+    await castChromecast.disconnect();
+    return true;
+  });
 }
 
 /**