refactor(app): compose session and player startup

Move streaming, live-session, hydration, local-player, combat, and teleport construction behind the typed Phase-7 boundary. Add exact-owner runtime bindings and focused spawn-claim classification so partial startup rolls back without retaining old session targets while preserving the accepted construction and frame dependencies.

Co-authored-by: Codex <codex@openai.com>

src/AcDream.App/Streaming/LocalPlayerTeleportController.cs

@@ -41,6 +41,17 @@ internal sealed class DeferredLocalPlayerTeleportNetworkSink
             throw new InvalidOperationException("The local teleport sink is already bound.");
     }
 
+    public IDisposable BindOwned(ILocalPlayerTeleportNetworkSink inner)
+    {
+        Bind(inner);
+        return new Binding(this, inner);
+    }
+
+    private void Unbind(ILocalPlayerTeleportNetworkSink expected)
+    {
+        _ = Interlocked.CompareExchange(ref _inner, null, expected);
+    }
+
     public void OnTeleportStarted(uint sequence) => Required().OnTeleportStarted(sequence);
 
     public void OfferDestination(
@@ -53,6 +64,23 @@ internal sealed class DeferredLocalPlayerTeleportNetworkSink
     private ILocalPlayerTeleportNetworkSink Required() =>
         _inner ?? throw new InvalidOperationException(
             "The local teleport sink was used before composition completed.");
+
+    private sealed class Binding : IDisposable
+    {
+        private DeferredLocalPlayerTeleportNetworkSink? _owner;
+        private readonly ILocalPlayerTeleportNetworkSink _expected;
+
+        public Binding(
+            DeferredLocalPlayerTeleportNetworkSink owner,
+            ILocalPlayerTeleportNetworkSink expected)
+        {
+            _owner = owner;
+            _expected = expected;
+        }
+
+        public void Dispose() =>
+            Interlocked.Exchange(ref _owner, null)?.Unbind(_expected);
+    }
 }
 
 internal interface ILocalPlayerTeleportInputLifetime