fix(playback): P2P peer discovery for Blossom videos + forced-torrent URL fallback (#30)

Two torrent-path robustness fixes surfaced while testing WebTorrent peering:

- streamVideo now sets announce: [...WSS_TRACKERS]. A .torrent-buffer add (Blossom companion piece-map) has an EMPTY embedded announce list, so without this it reached no tracker, found no WebRTC peers, and streamed webseed-only (looked like a stuck '1 peer'). WebTorrent merges these with any trackers already on the source.

- A forced-torrent playback now falls back to the hosted URL when the torrent DEFINITIVELY fails (e.g. a transient companion-lookup failure under relay congestion, or a dead swarm) instead of hard-erroring 'No playable source found'. Only triggers on real failure, not a slow swarm. Rollback noted inline.

Co-Authored-By: Claude Opus 4.8 <[email protected]>

js/services/playbackService.js

@@ -1288,8 +1288,19 @@ class PlaybackSession extends SimpleEventEmitter {
           }
         }
 
-        // Fallback to URL
-        if (httpsUrl && forcedSource !== "torrent") {
+        // Fallback to URL. Even when P2P was explicitly forced, a hosted URL is a
+        // better outcome than a hard "No playable source found" if the torrent
+        // DEFINITIVELY failed (e.g. a transient companion-lookup failure or a dead
+        // swarm). The torrent-first attempt above already ran — and, when there was
+        // no URL plan B, waited indefinitely — so we only reach here on real
+        // failure, not on a slow-but-working swarm.
+        // Rollback: restore `&& forcedSource !== "torrent"` to make forced P2P hard-fail.
+        if (httpsUrl) {
+          if (forcedSource === "torrent") {
+            this.service.log(
+              "[playVideoWithFallback] Forced torrent failed; falling back to the hosted URL."
+            );
+          }
           const urlResult = await attemptHostedPlayback();
           if (urlResult && urlResult.source === "url") {
             return urlResult;

js/webtorrent.js

@@ -941,7 +941,17 @@ export class TorrentClient {
       // Cap peer connections for the streaming torrent too. 30 is plenty to
       // saturate playback bandwidth while avoiding the WebRTC-handshake storm
       // that can peg the main thread (WebTorrent's default is 55).
-      const chromeOptions = { strategy: "sequential", maxConns: 30 };
+      // Announce to the WSS trackers explicitly. The magnet path already carries
+      // trackers (playbackUtils augments it), but a .torrent-buffer add
+      // (torrentFileBytes, from a Blossom video's companion event) has an EMPTY
+      // embedded announce list — without this it would reach no tracker, discover
+      // no WebRTC peers, and stream from the webseed only (looks like "1 peer").
+      // WebTorrent merges this with any trackers already on the source, deduped.
+      const chromeOptions = {
+        strategy: "sequential",
+        maxConns: 30,
+        announce: [...WSS_TRACKERS],
+      };
       /**
        * CRITICAL: Passing `urlList` ensures the client can stream from the webseed.
        * Without this, videos with 0 P2P peers will fail to play even if a valid