No buffering rings at the end of short videos; links never guess an AniList show

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

packages/core/lib/src/protocol.dart

@@ -559,12 +559,17 @@ class StateBroadcast {
   /// Buffer an in-set member needs before playback can go on, as the
   /// server's gate counts it: [RelayConstants.minBufferSecs], less near the
   /// end (mpv cannot buffer past it), none once finished.
-  double get bufferNeed {
+  double get bufferNeed => bufferNeedAt(DateTime.now().toUtc());
+
+  /// [bufferNeed] at [now]: while playing the position has moved on since
+  /// [serverTime] (the local clock is close enough for this).
+  double bufferNeedAt(DateTime now) {
     if (transport == 'finished') return 0;
     final d = (media?['duration'] as num?)?.toDouble() ?? 0;
     const full = RelayConstants.minBufferSecs;
     if (d <= 0) return full;
-    return (d - position - RelayConstants.endSlackSecs).clamp(0.0, full).toDouble();
+    final moved = transport == 'playing' ? now.difference(serverTime).inMilliseconds / 1000 : 0;
+    return (d - (position + moved) - RelayConstants.endSlackSecs).clamp(0.0, full).toDouble();
   }
 
   final int eventId;

packages/core/test/core_test.dart

@@ -193,4 +193,21 @@ void main() {
       expect((r.duration, r.mediaId), (0.0, 0));
     });
   });
+
+  test('bufferNeed counts the time played since the last event', () {
+    final t0 = DateTime.utc(2026, 1, 1);
+    final s = StateBroadcast(
+      eventId: 1,
+      transport: 'playing',
+      position: 0,
+      serverTime: t0,
+      mediaId: 1,
+      media: const {'name': 'clip', 'duration': 6.0},
+      members: const [],
+    );
+    expect(s.bufferNeedAt(t0), 4.0);
+    // 3 s in: 3 s left, minus the 2 s end slack.
+    expect(s.bufferNeedAt(t0.add(const Duration(seconds: 3))), closeTo(1.0, 1e-9));
+    expect(s.bufferNeedAt(t0.add(const Duration(seconds: 5))), 0);
+  });
 }