21.3 review fixes: guard superseded-seek failures; restore post-recovery retry

C6/AC8: IsStillActiveSeek() predicate guards all three SeekBeyondBuffer
failure exits, so a superseded seek never recovers over a newer seek's
state. AC6: empty scheduler routes to seekBeyondBuffer so a same-target
retry (seek or play) refetches instead of no-oping.

DeepDrftPublic.Client/Services/AudioPlayerService.cs

@@ -118,6 +118,16 @@ public abstract class AudioPlayerService : IPlayerService, IAsyncDisposable
                     IsPlaying = true;
                     IsPaused = false;
                 }
+                else if (IsPaused)
+                {
+                    // Play failed while the player is paused — the scheduler may be empty after a
+                    // failed refill (AC6 recovery). Re-issue a seek at the current position: the
+                    // seek path routes to seekBeyondBuffer when the scheduler is empty (Phase 21.3
+                    // fix), triggering a real refetch rather than returning "Streaming not ready".
+                    // We return early here; Seek owns its own state mutations and NotifyStateChanged.
+                    await Seek(CurrentTime);
+                    return;
+                }
             }
 
             if (!result.Success)
@@ -128,7 +138,7 @@ public abstract class AudioPlayerService : IPlayerService, IAsyncDisposable
             {
                 ErrorMessage = null;
             }
-            
+
             await NotifyStateChanged();
         }
         catch (Exception ex)