fix(client): a seek's first segments are held while it lands, not dropped

They are the new stream, header first. Dropped, a cast relay restarted at the
landing got no ftyp/moov and the receiver gave up; they are now replayed in
order once reinitAt/resumeAt is done.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

1 files changed, 36 insertions, 1 deletions

diff --git a/packages/meshbay-hub/src/meshbay_hub/static/video-player.js b/packages/meshbay-hub/src/meshbay_hub/static/video-player.js
index 2a4d2ea..4fa652b 100644
--- a/packages/meshbay-hub/src/meshbay_hub/static/video-player.js
+++ b/packages/meshbay-hub/src/meshbay_hub/static/video-player.js
@@ -438,6 +438,10 @@ function VideoPlayer({ entry, transportRef, gekRef, onClose, onDownload }) {
   const castRestartPendingRef = useRef(false);
   const castDeviceRef = useRef(null);
   const castRestartGenRef = useRef(0);
+  // Segments of the *new* stream that arrive while its seek is still landing
+  // (`reinitAt`/`resumeAt` wait on the SourceBuffer). Null when not holding.
+  const heldRef = useRef(null);
+  const holdGenRef = useRef(0);
   const landingPlayheadRef = useRef(false);
   // The current Screen Wake Lock sentinel, if the browser granted one — see
   // the effect below. Null on any platform/context that does not support it,
@@ -764,6 +768,7 @@ function VideoPlayer({ entry, transportRef, gekRef, onClose, onDownload }) {
           ranges: describeRanges(),
         });
         awaitingInitRef.current = true;
+        heldRef.current = null; holdGenRef.current++;
         // A seek supersedes a resume that had been asked for and not landed:
         // this one empties the buffer, and taking the resume branch on its
         // `stream_init` would leave the film we navigated away from in place.
@@ -798,6 +803,7 @@ function VideoPlayer({ entry, transportRef, gekRef, onClose, onDownload }) {
       });
       resumingRef.current = true;
       awaitingInitRef.current = true;
+      heldRef.current = null; holdGenRef.current++;
       seekTargetRef.current = null;
       outstandingRef.current = STREAM_WINDOW;
       console.log('[resume] request', +target.toFixed(1));
@@ -1064,7 +1070,23 @@ function VideoPlayer({ entry, transportRef, gekRef, onClose, onDownload }) {
             castRestartPendingRef.current = true;
           }
           const land = resuming ? resumeAt : reinitAt;
-          land(msg.start || 0).catch(() => {
+          // What follows this message on the ordered channel is the new
+          // stream, its header first. The landing waits on the SourceBuffer,
+          // and those segments used to arrive in that gap and be dropped as
+          // the old film's: the player kept its header from the start of the
+          // film and never noticed, but a cast relay restarted here got a
+          // stream beginning at a moof — no ftyp, no moov — and the receiver
+          // gave up on it within a second (measured on a phone). So they are
+          // held, and taken in order once the landing is done.
+          const hold = ++holdGenRef.current;
+          heldRef.current = [];
+          land(msg.start || 0).then(async () => {
+            while (holdGenRef.current === hold && heldRef.current && heldRef.current.length) {
+              await consumeSegment(heldRef.current.shift());
+            }
+            if (holdGenRef.current === hold) heldRef.current = null;
+          }).catch(() => {
+            if (holdGenRef.current === hold) heldRef.current = null;
             setError(t('video.err_transport'));
             setPhase('error');
           });
@@ -1178,6 +1200,12 @@ function VideoPlayer({ entry, transportRef, gekRef, onClose, onDownload }) {
         // for credit that cannot come. A race, which is why the same seek
         // worked twice and hung on the third.
         outstandingRef.current = Math.max(0, outstandingRef.current - 1);
+        // The new stream, arriving while its seek lands: kept, not dropped.
+        // Counted above already, so the replay must not count it again.
+        if (heldRef.current) {
+          if (!msg.file_id || msg.file_id === entry.id) heldRef.current.push(msg);
+          return;
+        }
         if (awaitingInitRef.current) {
           console.log('[seek] dropping segment (awaitingInit), outstanding:', outstandingRef.current);
         }
@@ -1190,6 +1218,13 @@ function VideoPlayer({ entry, transportRef, gekRef, onClose, onDownload }) {
         // would otherwise be decrypted against the wrong file — which fails,
         // loudly, in the console, for something that is simply not ours.
         if (msg.file_id && msg.file_id !== entry.id) return;
+        await consumeSegment(msg);
+      };
+
+      // Everything a segment goes through once it is known to belong to the
+      // stream being played: by arrival, or replayed after a landing.
+      const consumeSegment = async (msg) => {
+        if (cancelled) return;
         try {
           const plaintext = await window.MeshBayCrypto.decryptChunkBin(
             gekRef.current, entry.id, msg.segment_index, msg.nonce, msg.ct);