feat(render): Phase A8.F — RetailChaseCamera consumes the camera-collision probe

Add ICameraCollisionProbe? CollisionProbe { get; init; } to RetailChaseCamera.
Extend Update() with optional cellId/selfEntityId params (default 0) so all
existing callers compile unchanged. After the exponential-damping block (step 5)
and before publishing Position/View (step 6), sweep _dampedEye through the
probe when CameraDiagnostics.CollideCamera is true and a probe is wired in
(step 5b). The fade computation in step 7 then naturally uses the collided eye.
Null probe and cellId=0 both short-circuit cleanly. Three new xUnit tests
cover: probe-wired+flag-on publishes collided eye, flag-off skips probe,
null probe doesn't throw. All 30 RetailChaseCameraTests pass.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

src/AcDream.App/Rendering/RetailChaseCamera.cs

@@ -52,6 +52,14 @@ public sealed class RetailChaseCamera : ICamera
     /// <summary>Height of look-at anchor above the player's feet (m). Retail default 1.5.</summary>
     public float PivotHeight { get; set; } = 1.5f;
 
+    /// <summary>
+    /// Optional spring-arm collision probe. When set (and
+    /// <see cref="CameraDiagnostics.CollideCamera"/> is true), the damped eye
+    /// is swept from the head-pivot and stopped at the first wall. Null leaves
+    /// the eye uncollided (the default for tests and the legacy path).
+    /// </summary>
+    public ICameraCollisionProbe? CollisionProbe { get; init; }
+
     /// <summary>Computed translucency for the player mesh (0 = opaque, 1 = invisible). Read by GameWindow.</summary>
     public float PlayerTranslucency { get; private set; }
 
@@ -89,7 +97,9 @@ public sealed class RetailChaseCamera : ICamera
         Vector3 playerVelocity,
         bool isOnGround,
         Vector3 contactPlaneNormal,
-        float dt)
+        float dt,
+        uint cellId = 0,
+        uint selfEntityId = 0)
     {
         // 1. Push velocity into 5-frame ring, get average.
         PushVelocity(_velocityRing, ref _velocityCount, playerVelocity);
@@ -132,6 +142,14 @@ public sealed class RetailChaseCamera : ICamera
             _dampedForward = Vector3.Normalize(Vector3.Lerp(_dampedForward, targetForward, rAlpha));
         }
 
+        // 5b. Spring-arm collision (A8.F). Retail SmartBox::update_viewer
+        //     (0x00453ce0) sweeps viewer_sphere from the head-pivot to the
+        //     desired eye and uses the stopped position. Keeps the eye out of
+        //     walls so the A8.F camera-cell + portal side-tests stay stable.
+        //     A null probe or disabled flag leaves the eye unchanged.
+        if (CameraDiagnostics.CollideCamera && CollisionProbe is not null)
+            _dampedEye = CollisionProbe.SweepEye(pivotWorld, _dampedEye, cellId, selfEntityId);
+
         // 6. Publish renderer surface.
         Position = _dampedEye;
         View     = Matrix4x4.CreateLookAt(_dampedEye, _dampedEye + _dampedForward, new Vector3(0f, 0f, 1f));