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/Composition/SessionPlayerRuntimeBindings.cs

@@ -0,0 +1,95 @@
+using AcDream.App.Rendering;
+using AcDream.App.World;
+
+namespace AcDream.App.Composition;
+
+/// <summary>
+/// Named Phase-7 external edges. Releases run in reverse order; completed
+/// edges are removed immediately so an incomplete cleanup retries only the
+/// remaining work.
+/// </summary>
+internal sealed class SessionPlayerRuntimeBindings : IDisposable
+{
+    private readonly List<(string Name, IDisposable Binding)> _bindings = [];
+    private bool _deactivationStarted;
+
+    public void Adopt(string name, IDisposable binding)
+    {
+        ArgumentException.ThrowIfNullOrWhiteSpace(name);
+        ArgumentNullException.ThrowIfNull(binding);
+        ObjectDisposedException.ThrowIf(_deactivationStarted, this);
+        _bindings.Add((name, binding));
+    }
+
+    public void BindEntityReady(
+        EquippedChildRenderController source,
+        Action<LiveEntityReadyCandidate> handler)
+    {
+        ArgumentNullException.ThrowIfNull(source);
+        ArgumentNullException.ThrowIfNull(handler);
+        source.EntityReady += handler;
+        Adopt(
+            "equipped-child entity ready",
+            new DelegateBinding(() => source.EntityReady -= handler));
+    }
+
+    public void BindAppearanceApplied(
+        LiveEntityHydrationController source,
+        Action<uint> handler)
+    {
+        ArgumentNullException.ThrowIfNull(source);
+        ArgumentNullException.ThrowIfNull(handler);
+        source.AppearanceApplied += handler;
+        Adopt(
+            "live appearance applied",
+            new DelegateBinding(() => source.AppearanceApplied -= handler));
+    }
+
+    public void Dispose()
+    {
+        if (_deactivationStarted && _bindings.Count == 0)
+            return;
+        _deactivationStarted = true;
+
+        List<Exception>? failures = null;
+        for (int i = _bindings.Count - 1; i >= 0; i--)
+        {
+            (string name, IDisposable binding) = _bindings[i];
+            try
+            {
+                binding.Dispose();
+                _bindings.RemoveAt(i);
+            }
+            catch (Exception failure)
+            {
+                (failures ??= []).Add(new InvalidOperationException(
+                    $"Session/player binding '{name}' did not detach.",
+                    failure));
+            }
+        }
+
+        if (failures is not null)
+        {
+            throw new AggregateException(
+                "Session/player binding cleanup remains incomplete.",
+                failures);
+        }
+    }
+
+    private sealed class DelegateBinding : IDisposable
+    {
+        private Action? _release;
+
+        public DelegateBinding(Action release) =>
+            _release = release ?? throw new ArgumentNullException(nameof(release));
+
+        public void Dispose()
+        {
+            Action? release = _release;
+            if (release is null)
+                return;
+            release();
+            _release = null;
+        }
+    }
+}