refactor(world): extract live entity teardown

src/AcDream.App/Physics/RemoteMovementObservationTracker.cs

@@ -0,0 +1,27 @@
+using System.Numerics;
+
+namespace AcDream.App.Physics;
+
+/// <summary>
+/// Session-scoped observation timestamps used to infer when a remote
+/// locomotion cycle has stopped. Canonical live identity remains in
+/// <c>LiveEntityRuntime</c>; this owner contains only derived observer state.
+/// </summary>
+internal sealed class RemoteMovementObservationTracker
+{
+    private readonly Dictionary<uint, (Vector3 Pos, DateTime Time)> _lastMove = new();
+
+    internal (Vector3 Pos, DateTime Time) this[uint serverGuid]
+    {
+        set => _lastMove[serverGuid] = value;
+    }
+
+    internal bool TryGetValue(
+        uint serverGuid,
+        out (Vector3 Pos, DateTime Time) observation) =>
+        _lastMove.TryGetValue(serverGuid, out observation);
+
+    internal bool Remove(uint serverGuid) => _lastMove.Remove(serverGuid);
+
+    internal void Clear() => _lastMove.Clear();
+}