fix(session): confirm routed delivery and keep playback state with the owner

Emby.Server.Implementations/Session/RemoteSessionController.cs

@@ -13,7 +13,7 @@ namespace Emby.Server.Implementations.Session;
 
 /// <summary>
 /// Stands in for the websocket of a session another instance holds: messages are forwarded to that
-/// instance, which writes them to the connection it owns.
+/// instance, which writes them to the connection it owns and reports back whether it did.
 /// </summary>
 public sealed class RemoteSessionController : ISessionController
 {
@@ -56,7 +56,7 @@ public sealed class RemoteSessionController : ISessionController
             Data = JsonSerializer.Serialize(data, JsonDefaults.Options)
         };
 
-        var delivered = await _bus.PublishAsync(
+        var delivered = await _bus.RequestAsync(
             _ownerPod,
             new PodMessage
             {
@@ -65,12 +65,12 @@ public sealed class RemoteSessionController : ISessionController
             },
             cancellationToken).ConfigureAwait(false);
 
-        if (delivered == 0)
+        if (!delivered)
         {
-            _logger.LogWarning("Instance {OwnerPod} holds session {SessionId} but is not listening; the {MessageType} message was not delivered.", _ownerPod, _sessionId, name);
+            _logger.LogWarning("Instance {OwnerPod} did not write the {MessageType} message for session {SessionId} to a connection.", _ownerPod, name, _sessionId);
 
             throw new ResourceNotFoundException(
-                string.Format(CultureInfo.InvariantCulture, "The instance holding session {0} is unreachable.", _sessionId));
+                string.Format(CultureInfo.InvariantCulture, "No instance holds a connection to session {0}.", _sessionId));
         }
     }
 }