fix(session): tie directory ownership to the live connection

Ownership is claimed with a Lua check-and-set keyed on the instance holding
the websocket, routing prefers a live controller over a local copy, the
session list deduplicates by owner, removal is ownership-checked, undelivered
routed messages surface, single-session lookups stop scanning the keyspace and
directory writes leave the request path bounded by a timeout.

Emby.Server.Implementations/Session/RemoteSessionController.cs

@@ -1,10 +1,13 @@
 using System;
+using System.Globalization;
 using System.Text.Json;
 using System.Threading;
 using System.Threading.Tasks;
 using Jellyfin.Extensions.Json;
+using MediaBrowser.Common.Extensions;
 using MediaBrowser.Controller.Session;
 using MediaBrowser.Model.Session;
+using Microsoft.Extensions.Logging;
 
 namespace Emby.Server.Implementations.Session;
 
@@ -15,6 +18,7 @@ namespace Emby.Server.Implementations.Session;
 public sealed class RemoteSessionController : ISessionController
 {
     private readonly IPodMessageBus _bus;
+    private readonly ILogger _logger;
     private readonly string _ownerPod;
     private readonly string _sessionId;
 
@@ -22,27 +26,27 @@ public sealed class RemoteSessionController : ISessionController
     /// Initializes a new instance of the <see cref="RemoteSessionController"/> class.
     /// </summary>
     /// <param name="bus">The cross-instance bus.</param>
+    /// <param name="logger">The logger.</param>
     /// <param name="ownerPod">The instance holding the connection.</param>
     /// <param name="sessionId">The session identifier.</param>
-    /// <param name="isSessionActive">Whether the owner reported the session as active.</param>
     /// <param name="supportsMediaControl">Whether the owner reported the session as controllable.</param>
-    public RemoteSessionController(IPodMessageBus bus, string ownerPod, string sessionId, bool isSessionActive, bool supportsMediaControl)
+    public RemoteSessionController(IPodMessageBus bus, ILogger logger, string ownerPod, string sessionId, bool supportsMediaControl)
     {
         _bus = bus;
+        _logger = logger;
         _ownerPod = ownerPod;
         _sessionId = sessionId;
-        IsSessionActive = isSessionActive;
         SupportsMediaControl = supportsMediaControl;
     }
 
     /// <inheritdoc />
-    public bool IsSessionActive { get; }
+    public bool IsSessionActive => true;
 
     /// <inheritdoc />
     public bool SupportsMediaControl { get; }
 
     /// <inheritdoc />
-    public Task SendMessage<T>(SessionMessageType name, Guid messageId, T data, CancellationToken cancellationToken)
+    public async Task SendMessage<T>(SessionMessageType name, Guid messageId, T data, CancellationToken cancellationToken)
     {
         var routed = new RoutedSessionMessage
         {
@@ -52,14 +56,21 @@ public sealed class RemoteSessionController : ISessionController
             Data = JsonSerializer.Serialize(data, JsonDefaults.Options)
         };
 
-        _bus.Publish(
+        var delivered = await _bus.PublishAsync(
             _ownerPod,
             new PodMessage
             {
                 Kind = RoutedSessionMessage.Kind,
                 Payload = JsonSerializer.Serialize(routed, JsonDefaults.Options)
-            });
+            },
+            cancellationToken).ConfigureAwait(false);
 
-        return Task.CompletedTask;
+        if (delivered == 0)
+        {
+            _logger.LogWarning("Instance {OwnerPod} holds session {SessionId} but is not listening; the {MessageType} message was not delivered.", _ownerPod, _sessionId, name);
+
+            throw new ResourceNotFoundException(
+                string.Format(CultureInfo.InvariantCulture, "The instance holding session {0} is unreachable.", _sessionId));
+        }
     }
 }