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/Input/CameraPointerInputController.cs

@@ -245,6 +245,20 @@ internal sealed class CameraPointerInputController
         _gameplayFrame = gameplayFrame;
     }
 
+    public IDisposable BindGameplayFrameOwned(
+        GameplayInputFrameController gameplayFrame)
+    {
+        ArgumentNullException.ThrowIfNull(gameplayFrame);
+        if (_gameplayFrame is not null)
+        {
+            throw new InvalidOperationException(
+                "The raw pointer owner already has a gameplay frame.");
+        }
+
+        _gameplayFrame = gameplayFrame;
+        return new GameplayFrameBinding(this, gameplayFrame);
+    }
+
     public void UnbindGameplayFrame(GameplayInputFrameController gameplayFrame)
     {
         ArgumentNullException.ThrowIfNull(gameplayFrame);
@@ -252,6 +266,24 @@ internal sealed class CameraPointerInputController
             _gameplayFrame = null;
     }
 
+    private sealed class GameplayFrameBinding : IDisposable
+    {
+        private CameraPointerInputController? _owner;
+        private readonly GameplayInputFrameController _expected;
+
+        public GameplayFrameBinding(
+            CameraPointerInputController owner,
+            GameplayInputFrameController expected)
+        {
+            _owner = owner;
+            _expected = expected;
+        }
+
+        public void Dispose() =>
+            Interlocked.Exchange(ref _owner, null)?
+                .UnbindGameplayFrame(_expected);
+    }
+
     public void HandleFocusChanged(bool focused)
     {
         if (!focused)