docs(render): Phase A8.F — camera-collision implementation plan

Bite-sized TDD plan for the swept-sphere camera collision: CollideCamera flag,
ICameraCollisionProbe + PhysicsCameraCollisionProbe (reuses ResolveWithTransition),
RetailChaseCamera slot-in, GameWindow wiring, Camera-menu toggle, visual
acceptance. Also refines the spec from planning findings: the InitPath +radius
sphere-center offset (ToSpherePath/FromSpherePath z-shift) and the deterministic
probe test scope (z-offset round-trip + cellId==0 guard; collision correctness
rides the existing sweep suite + visual).

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

docs/superpowers/specs/2026-05-29-a8f-camera-collision-design.md

@@ -130,9 +130,13 @@ public interface ICameraCollisionProbe
 public Vector3 SweepEye(Vector3 pivot, Vector3 desiredEye, uint cellId, uint selfEntityId)
 {
     if (cellId == 0) return desiredEye;                 // no starting cell → can't sweep
+    // InitPath offsets sphere0's center up by radius (foot-capsule convention),
+    // but retail's viewer_sphere center is (0,0,0). Shift the path down by radius
+    // so the SPHERE CENTER travels pivot→eye, then add it back to the result.
+    var zoff = new Vector3(0f, 0f, 0.3f);
     var r = _physics.ResolveWithTransition(
-        currentPos:     pivot,
-        targetPos:      desiredEye,
+        currentPos:     pivot - zoff,
+        targetPos:      desiredEye - zoff,
         cellId:         cellId,
         sphereRadius:   0.3f,        // retail viewer_sphere radius
         sphereHeight:   0f,          // single sphere (no head sphere)
@@ -144,7 +148,7 @@ public Vector3 SweepEye(Vector3 pivot, Vector3 desiredEye, uint cellId, uint sel
                                                // camera sweeps out of the #98
                                                // IsPlayer capture filter
         movingEntityId: selfEntityId);         // skip the player's own ShadowEntry
-    return r.Position;               // = sp.CheckPos, the swept stop position
+    return r.Position + zoff;        // r.Position = sp.CheckPos (path pt); + zoff = eye
 }
 ```
 
@@ -234,11 +238,13 @@ inside the player mesh) when backed into a corner.
   - probe returns a pulled-in eye → published `Position`/`View` use the collided
     eye; fade increases.
   - `CollideCamera = false` → probe never consulted.
-- `PhysicsCameraCollisionProbe` against fixtures (reuse the issue-#98 cell +
-  GfxObj fixtures already in the test tree):
-  - clear path → eye unchanged;
-  - wall/shell between pivot and desiredEye → eye stops short (does not penetrate);
-  - `selfEntityId` set → sweep does not collide with the player's own ShadowEntry.
+- `PhysicsCameraCollisionProbe` deterministic units (no heavy fixture setup):
+  - `ToSpherePath`/`FromSpherePath` z-offset round-trip;
+  - `cellId == 0` guard → returns `desiredEye` unchanged.
+  Collision correctness itself (eye stops at a wall/shell; self-skip) is already
+  covered by the exhaustive `ResolveWithTransition` / `BSPQuery` suites and is
+  confirmed end-to-end by the visual acceptance below — re-proving it at the probe
+  layer would duplicate that coverage with brittle fixture wiring.
 
 **Visual (acceptance):** with `ACDREAM_A8_INDOOR_BRANCH=1`, walk into a Holtburg
 cottage and its cellar:
@@ -263,9 +269,12 @@ Compare `ACDREAM_CAMERA_COLLIDE=0` vs default to confirm the flag isolates the f
    retail's `find_valid_position` during implementation and confirm whether it
    slides or hard-stops; match it. Both keep the eye out of walls, so this does
    not change the architecture.
-2. **`sphereHeight: 0f`.** Confirm `SpherePath.InitPath` with height 0 yields a
-   single sphere (no degenerate coincident head sphere). If not, pass a tiny
-   height or a single-sphere init.
+2. **`sphereHeight: 0f` — RESOLVED.** `SpherePath.InitPath` with height 0 yields a
+   single sphere (`NumSphere = 1`, `TransitionTypes.cs:534-537`). It also offsets
+   sphere0's center to `pathPos + (0,0,radius)` (foot-capsule convention) whereas
+   retail's `viewer_sphere` center is (0,0,0); the probe compensates with the
+   `ToSpherePath`/`FromSpherePath` z-shift (§5.1) so the sphere center travels
+   pivot→eye.
 3. **Probe construction order.** The `PhysicsEngine` must exist before the
    `RetailChaseCamera` constructions at `GameWindow.cs:10693/:10826`; confirm
    lifetime ordering or make the probe field settable post-construction.