checkpoint: preserve user-gated FW closeout fixes

src/AcDream.App/Rendering/Walk/WalkProductionFrameContext.cs

@@ -25,8 +25,9 @@ namespace AcDream.App.Rendering.Walk;
 /// true eye ray (near/far unprojection) are observably equivalent to
 /// retail's exact construction for this contract.
 ///
-/// One instance is a per-frame value (like <c>WalkTraceReplayContext</c>):
-/// construct fresh each frame with that frame's camera pose.
+/// Production retains one instance per renderer and rebinds its frame-local
+/// camera values through <see cref="Reset"/>. The registries and grow-only
+/// active-view scratch remain renderer-lifetime owners.
 /// </summary>
 public sealed class WalkProductionFrameContext : IWalkFrameContext, IRetailFrameWalkContext
 {
@@ -35,19 +36,28 @@ public sealed class WalkProductionFrameContext : IWalkFrameContext, IRetailFrame
 
     private sealed class InverseViewProjectionRayCaster : IWalkRayCaster
     {
-        private readonly Matrix4x4 _inverseViewProjection;
-        private readonly float _viewportWidth;
-        private readonly float _viewportHeight;
+        private Matrix4x4 _inverseViewProjection;
+        private float _viewportWidth;
+        private float _viewportHeight;
 
         public InverseViewProjectionRayCaster(
             Matrix4x4 viewProjection, float viewportWidth, float viewportHeight)
+            => Reset(viewProjection, viewportWidth, viewportHeight);
+
+        internal void Reset(
+            Matrix4x4 viewProjection, float viewportWidth, float viewportHeight)
         {
-            if (!Matrix4x4.Invert(viewProjection, out _inverseViewProjection))
+            if (!Matrix4x4.Invert(viewProjection, out Matrix4x4 inverseViewProjection))
             {
                 throw new ArgumentException(
                     "The walk's view-projection matrix must be invertible.",
                     nameof(viewProjection));
             }
+            // Publish only after validation succeeds. Matrix4x4.Invert writes
+            // its out value even on failure; assigning the field directly
+            // would silently corrupt the retained ray caster for the next
+            // report-and-continue frame.
+            _inverseViewProjection = inverseViewProjection;
             _viewportWidth = viewportWidth;
             _viewportHeight = viewportHeight;
         }
@@ -72,8 +82,8 @@ public sealed class WalkProductionFrameContext : IWalkFrameContext, IRetailFrame
 
     private readonly CellVisibility _cells;
     private readonly WalkBuildingRegistry _buildings;
-    private readonly Matrix4x4 _viewProjection;
-    private readonly IWalkRayCaster _rays;
+    private Matrix4x4 _viewProjection;
+    private readonly InverseViewProjectionRayCaster _rays;
 
     private Vector2[] _activeViewVerts = new Vector2[32];
     private int _activeViewVertCount;
@@ -89,19 +99,39 @@ public sealed class WalkProductionFrameContext : IWalkFrameContext, IRetailFrame
     {
         _cells = cells ?? throw new ArgumentNullException(nameof(cells));
         _buildings = buildings ?? throw new ArgumentNullException(nameof(buildings));
+        _rays = new InverseViewProjectionRayCaster(
+            viewProjection, viewportWidth, viewportHeight);
+        Reset(worldViewpoint, forward, viewProjection, viewportWidth, viewportHeight);
+    }
+
+    /// <summary>
+    /// FW6 allocation closeout: rebind this retained context to one frame's
+    /// camera values while preserving its active-view scratch. The cell and
+    /// building registries are lifetime owners and therefore never change.
+    /// </summary>
+    internal void Reset(
+        Vector3 worldViewpoint,
+        Vector3 forward,
+        Matrix4x4 viewProjection,
+        float viewportWidth,
+        float viewportHeight)
+    {
+        // Validate/invert before publishing any new frame value so a bad
+        // camera matrix leaves the previous usable binding intact.
+        _rays.Reset(viewProjection, viewportWidth, viewportHeight);
         WorldViewpoint = worldViewpoint;
         _viewProjection = viewProjection;
         ViewportWidth = viewportWidth;
         ViewportHeight = viewportHeight;
-        _rays = new InverseViewProjectionRayCaster(viewProjection, viewportWidth, viewportHeight);
+        _activeViewVertCount = 0;
         // The retail CY near plane: N = forward, d = -dot(eye, forward) - znear.
         CyPlane = new WalkPlane(forward, -Vector3.Dot(worldViewpoint, forward) - ZNear);
     }
 
-    public Vector3 WorldViewpoint { get; }
-    public float ViewportWidth { get; }
-    public float ViewportHeight { get; }
-    public WalkPlane CyPlane { get; }
+    public Vector3 WorldViewpoint { get; private set; }
+    public float ViewportWidth { get; private set; }
+    public float ViewportHeight { get; private set; }
+    public WalkPlane CyPlane { get; private set; }
     public IWalkRayCaster Rays => _rays;
     public IWalkFrameContext CellContext => this;