004 — Coalesce concurrent resolveStreams calls

Objective

resolveStreams(videoId) checks streamCache but has no in-flight map, so two requests for the same id that arrive before the first finishes (a warm-up + the real play, two devices, the media cache's getInfo + /api/streams) each spawn a ~6 s yt-dlp -J. After this plan, concurrent callers share ONE promise; a failure is not cached (the next call retries).

Context the executor must NOT rediscover

server/server.js:457-494:

async function resolveStreams(videoId) {
  const now = Date.now();
  const cached = streamCache.get(videoId);
  if (cached && now < cached.expiresAt) return cached;

  const out = await runYtdlpResilient(['-J', '--no-warnings', `https://www.youtube.com/watch?v=${videoId}`]);
  const info = JSON.parse(out);
  ...
  streamCache.set(videoId, entry);
  return entry;
}

streamCache and STREAM_CACHE_MAX are declared just above it.

Steps

server/server.js — rename the existing function resolveStreams to resolveStreamsUncached (definition only; body unchanged).

Directly after that function add:

// 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;
}

All existing callers keep calling resolveStreams (it still returns a Promise).

Create server/streams-inflight.test.js? — NO. Keep it in-file; instead verify with the script below.

Out of scope / do NOT touch

Cache TTL logic, runYtdlpResilient, format filtering.

Verification

cd /home/user/ytplayer/server && grep -n "function resolveStreams\|function resolveStreamsUncached\|inflightStreams" server.js
bun build server.js --target=bun --outdir=/tmp/ytp-check >/dev/null && echo SERVER_OK
bun run test 2>&1 | grep -E "^ *[0-9]+ (pass|fail)"

Expected: both functions + map present, SERVER_OK, all server test files 0 fail.

Report format (executor: follow exactly)

Output ONLY the following, no other prose:

git diff (unified) of all changes.
Raw output of the Verification commands.
Findings: — max 10 lines.

Do not commit. Do not push. Do not touch files outside the Steps.

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