Restructure step 5: one media pipeline on a player host

- PlayerHost port (MediaKitHost): players by role, pins, hwdec policy,
  render probe, log routing, disposal order; the only media_kit user.
- MediaPipeline: plan (one pure switch over state, origin, caps,
  presence) -> resolve -> open (prepared player promoted, else fresh)
  -> ready; commands queued during a switch apply once (P15); viewers
  play the buffer and wait for a dropped source without seek loops (D6).
- Every web page resolved by our yt-dlp into an EDL with headers and
  cookies (danmaku excluded); mpv's ytdl_hook no longer used (ytdl=no).
- D11: sign-in errors say which cookies were used and whether they hold
  any for the site.
- Relay: 256 KiB slices read as they fill, superseded pulls released
  (seek-to-play ~4.2 s -> ~2.8 s, P29); own Jellyfin relay channel only
  when someone needs it (P28).
- STARSYNC_SMOKE run and a Windows CI smoke step after the build.

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

apps/desktop/lib/src/session/status.dart

@@ -210,6 +210,20 @@ StatusLine? _line(StatusFacts f, StateBroadcast? r, MemberView? self, SourceTrou
     return StatusLine(StatusKind.problem, "Can't play this: ${f.playerError}",
         level: StatusLevel.error, action: StatusAction.reload, short: "Can't play this");
   }
+  // The server holds everyone for the relay's source (D6): a viewer's
+  // buffer ran dry while it is gone.
+  if (r.transport == 'held' && r.hold?.reason == HoldReason.source) {
+    final relayed = stateMediaRelay(r);
+    final id = relayed?.source ?? '';
+    final name = source?.name ??
+        r.members.where((m) => m.id == id).firstOrNull?.name ??
+        f.names?[id] ??
+        'the member passing it on';
+    return StatusLine(StatusKind.waiting, 'Waiting for $name',
+        detail: "$name's connection dropped; what the server had has played",
+        level: StatusLevel.warn,
+        short: 'Waiting for $name');
+  }
   // The relay: what everyone reads comes through the server.
   final relay = f.ownPlan ? null : stateMediaRelay(r);
   if (relay != null && relay.source != f.selfId) {