feat(3d): Fix ObjectType::PLANE scaling and consolidate ObjectType mapping

- Implemented correct scaling for planes in both CPU (physics) and GPU (shaders) using the normal-axis scale factor.
- Consolidated ObjectType to type_id mapping in Renderer3D to ensure consistency and support for CUBE.
- Fixed overestimation of distance for non-uniformly scaled ground planes, which caused missing shadows.
- Updated documentation and marked Task A.2 as completed.

1 files changed, 10 insertions, 0 deletions

diff --git a/doc/COMPLETED.md b/doc/COMPLETED.md
index cd448bf..148e410 100644
--- a/doc/COMPLETED.md
+++ b/doc/COMPLETED.md
@@ -2,6 +2,16 @@
 
 This file tracks recently completed tasks, organized by completion date.
 
+## Recently Completed (February 8, 2026)
+
+- [x] **3D Rendering & Shadow Improvements (Task A)** (February 8, 2026)
+    - [x] **Task A.1 (Shadow Investigation)**: Investigated mesh shadows appearing as bounding boxes. Documented that this is a design limitation of the hybrid renderer (AABB proxy for meshes in SDF pass). Created `doc/DEBUG_SHADOWS.md` with detailed analysis.
+    - [x] **Task A.2 (Plane Scaling Fix)**: Fixed `ObjectType::PLANE` distance calculation for non-uniform scaling.
+      - **Shader Fix**: Updated `map_scene` in both Linear and BVH pipelines to use normal-axis scale factor for planes.
+      - **Physics Fix**: Updated `PhysicsSystem::sample_sdf` to correctly scale plane distances on the CPU.
+      - **Mapping Cleanup**: Consolidated `ObjectType` to `type_id` mapping in `Renderer3D` and added support for `ObjectType::CUBE` in the shader path.
+    - **Result**: Ground planes with extreme non-uniform scaling now cast and receive shadows correctly, and physics collisions are accurate.
+
 ## Recently Completed (February 7, 2026)
 
 - [x] **Audio Peak Measurement & Test Coverage Improvements** (February 7, 2026)