Coalesce concurrent resolveStreams calls for the same video

plans/INDEX.md

@@ -11,7 +11,7 @@ green, app boots with no JS errors, P2P on by default, offline boot works).
 | 001 | 001-perf-timing-marks-105acc | Add startup, search and play timing marks plus yt-dlp duration logs | done | Add startup, search and play timing marks plus yt-dlp duration logs | baseline numbers for the rest |
 | 002 | 002-compress-and-etag-shell-bd459c | Serve the app shell gzip/brotli-compressed with ETags | done | Serve the app shell gzip/brotli-compressed with ETags | app.js 426 KB → 94 KB (br) |
 | 003 | 003-self-host-fonts-89466b | Self-host the three web fonts and drop the render-blocking Google Fonts CSS | done | Self-host the three web fonts and drop the render-blocking Google Fonts CSS | needs network once; CSP font-src fix |
-| 004 | 004-coalesce-stream-resolves-a92d40 | Coalesce concurrent resolveStreams calls for the same video | in-progress |  |  |
+| 004 | 004-coalesce-stream-resolves-a92d40 | Coalesce concurrent resolveStreams calls for the same video | done | Coalesce concurrent resolveStreams calls for the same video |  |
 | 005 | 005-warm-streams-on-intent-47b3d3 | Warm the stream cache for likely next plays | queued | | cold play 7.5 s → cached 1.2 s |
 | 006 | 006-innertube-search-48066b | Answer searches from YouTube InnerTube directly with yt-dlp fallback | queued | | search 4–5 s → ~0.8 s |
 | 007 | 007-ytdlp-worker-045800 | Keep one long-lived yt-dlp worker process instead of spawning per call | queued | | ~1 s per yt-dlp call |

plans/done/004-coalesce-stream-resolves-a92d40.md

@@ -83,3 +83,9 @@ Output ONLY the following, no other prose:
 3. `Findings:` — max 10 lines.
 
 Do not commit. Do not push. Do not touch files outside the Steps.
+
+## Execution log
+
+- Executor: in-session Agent (haiku). Attempts: 1. Fix rounds: 0.
+- Orchestrator re-ran Verification: both functions and `inflightStreams` present, `bun build` ok, `bun run test` all 5 server files 0 fail (media-cache 23 pass is the original baseline).
+- Executor Findings (verbatim): Plan executed successfully. Both renamed function and wrapper present in correct location. In-flight map correctly coalesces concurrent calls. All 58 server tests pass. Build completes with no errors. No deviations from plan requirements.

server/server.js

@@ -459,7 +459,7 @@ function parseExpiry(url) {
 // Resolve (and briefly cache) a video's playable formats via yt-dlp -J. The
 // cache spares a fresh ~2-3s yt-dlp run on every Range request the media
 // element fires; its TTL is bounded a minute inside the URLs' own expiry.
-async function resolveStreams(videoId) {
+async function resolveStreamsUncached(videoId) {
   const now = Date.now();
   const cached = streamCache.get(videoId);
   if (cached && now < cached.expiresAt) return cached;
@@ -498,6 +498,20 @@ async function resolveStreams(videoId) {
   return entry;
 }
 
+// One yt-dlp -J per video at a time: concurrent callers (warm-up + play,
+// two devices, the media cache's getInfo) share the in-flight promise.
+const inflightStreams = new Map(); // videoId -> Promise<entry>
+function resolveStreams(videoId) {
+  const cached = streamCache.get(videoId);
+  if (cached && Date.now() < cached.expiresAt) return Promise.resolve(cached);
+  let p = inflightStreams.get(videoId);
+  if (!p) {
+    p = resolveStreamsUncached(videoId).finally(() => inflightStreams.delete(videoId));
+    inflightStreams.set(videoId, p);
+  }
+  return p;
+}
+
 const isVideoFmt = (f) => f.vcodec && f.vcodec !== 'none';
 const isAudioFmt = (f) => f.acodec && f.acodec !== 'none';