docs: update scene runtime and debug toggles

- Drop SceneShadowWarmup section, document centralized shadow config.
- Document the localized Suspense boundaries in World.tsx.
- Document the new player model and octree debug visualizations.
- Open note about intermittent first-load shadow rendering.

docs/technical/three-debugging.md

@@ -20,3 +20,50 @@ If DevTools still opens a bundled file, stop the dev server, clear Vite's cached
 rm -rf node_modules/.vite
 npm run dev:three-debug
 ```
+
+## Visual debug toggles
+
+The `Debug` folder of the runtime debug GUI exposes inspection toggles backed by
+`src/managers/stores/useDebugVisualsStore.ts`:
+
+- **Show Player Model** — renders the main character GLTF in front of the
+  current camera (`src/components/debug/DebugPlayerModel.tsx`). The model is
+  positioned in camera-local space so it stays visible regardless of pitch.
+- **Show Octree** — overlays the collision octree as colored line segments,
+  one wireframe per spatial cell (`src/components/debug/DebugOctreeVisualization.tsx`).
+  Cells are colored by depth. Use it to inspect collision precision around
+  doorways or passages.
+- **Octree Max Depth** — caps how deep the octree visualization recurses
+  (default 6). Increase to see leaf-level subdivisions; decrease to keep the
+  scene readable when the tree is large.
+
+The octree visualization reads the live `Octree` instance from `World`. The
+mesh uses `depthTest: false` and a high `renderOrder`, so cells stay visible
+through opaque geometry.
+
+## Shadow rendering intermittence (open investigation)
+
+Shadows occasionally fail to render on initial load even though the
+`Lighting` configuration runs to completion (verified through diagnostic logs).
+The issue is not deterministic across runs with identical config. Suspected
+contributors:
+
+- WebGL context restoration timing (`webglcontextrestored` rebinds shadow map
+  state in `src/pages/page.tsx`).
+- First-frame shadow map being rendered before any mesh has its
+  `castShadow`/`receiveShadow` flag set; `autoUpdate=true` should fix it on the
+  next frame, but a single dropped frame is still visible at very first paint.
+- HMR/state interactions in dev mode that do not occur in production builds.
+
+Mitigations already applied:
+
+- Shadow config centralized in `src/data/world/lightingConfig.ts`
+  (`bias=0`, `normalBias=0`, `cameraSize=95`, matching the historically working
+  values from `develop`).
+- Late-suspension Suspense boundaries in `World.tsx` to prevent global scene
+  remounts that would re-run shadow setup mid-load.
+
+If the issue reproduces in production, capture a screenshot plus the
+`[diag]`-style logs from `useOctreeGraphNode`, `Lighting`, and `GameMapCollision`
+to confirm whether the third configuration pass is happening (which would
+indicate a remaining suspending hook outside the existing Suspense boundaries).