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/World/LiveEntityHydrationPorts.cs

@@ -41,9 +41,37 @@ internal sealed class DeferredLiveEntityParentAcceptance
             throw new InvalidOperationException("Live parent acceptance is already bound.");
     }
 
+    public IDisposable BindOwned(Func<ParentEvent.Parsed, bool> accept)
+    {
+        Bind(accept);
+        return new Binding(this, accept);
+    }
+
+    private void Unbind(Func<ParentEvent.Parsed, bool> expected)
+    {
+        _ = Interlocked.CompareExchange(ref _accept, null, expected);
+    }
+
     public bool TryAccept(ParentEvent.Parsed update) =>
         (_accept ?? throw new InvalidOperationException(
             "Live parent acceptance must be bound before a session starts."))(update);
+
+    private sealed class Binding : IDisposable
+    {
+        private DeferredLiveEntityParentAcceptance? _owner;
+        private readonly Func<ParentEvent.Parsed, bool> _expected;
+
+        public Binding(
+            DeferredLiveEntityParentAcceptance owner,
+            Func<ParentEvent.Parsed, bool> expected)
+        {
+            _owner = owner;
+            _expected = expected;
+        }
+
+        public void Dispose() =>
+            Interlocked.Exchange(ref _owner, null)?.Unbind(_expected);
+    }
 }
 
 internal sealed class LiveEntityReadyPublisher : ILiveEntityReadyPublisher