fix(cnn_v3): shadow pass — 5 bugs fixed, labels in gbuf_viewHEADmain

1. Camera Y-inversion: proj.m[5] = -proj.m[5] in upload_scene_data
   + WGPUFrontFace_CCW on raster pipeline.
2. Shadow formula: replace shadowWithStoredDistance with 64-step
   IQ soft shadow (8*d/t, unbounded).
3. Local→world SDF scale: d *= length(obj.model[0].xyz).
4. Shadow bias: use rasterized normal from normal_mat_tex (binding 4)
   instead of light direction — fixes terminator self-shadow on spheres.
5. ShaderComposer: GBufViewEffect now resolves #include via
   ShaderComposer::Get().Compose().

Also: per-tile channel labels in gbuf_view.wgsl via debug_str.
Scene simplified to 1 cube + 1 sphere for debugging (restore TODO).
Scale propagation for pulsating sphere confirmed correct end-to-end.

handoff(Gemini): shadow validated. Next: restore full scene in
GBufferEffect::set_scene() (20 cubes + 4 spheres, 2 lights), then
run training pass per cnn_v3/docs/HOWTO.md §3.

1 files changed, 8 insertions, 0 deletions

diff --git a/doc/COMPLETED.md b/doc/COMPLETED.md
index 072c92f..a3a988c 100644
--- a/doc/COMPLETED.md
+++ b/doc/COMPLETED.md
@@ -36,6 +36,14 @@ Completed task archive. See `doc/archive/` for detailed historical documents.
 
 ## March 2026
 
+- [x] **CNN v3 shadow pass debugging** — Fixed 5 independent bugs in `gbuf_shadow.wgsl` + `gbuffer_effect.cc`:
+  1. **Camera Y-inversion**: `mat4::perspective` negates Y for post-process chain; fixed with `proj.m[5] = -proj.m[5]` in `upload_scene_data` + `WGPUFrontFace_CCW` on raster pipeline.
+  2. **Shadow formula**: replaced `shadowWithStoredDistance` (20 steps, bounded) with 64-step IQ soft shadow (`res = min(res, 8.0*d/t)`, unbounded march).
+  3. **Local→world SDF scale**: `sdBox/sdSphere` return local-space distance; fixed with `d *= length(obj.model[0].xyz)`.
+  4. **Shadow bias**: replaced light-direction bias (fails at terminator) with rasterized surface normal from `normal_mat_tex` (binding 4); `bias_pos = world + nor * 0.05`.
+  5. **ShaderComposer**: `GBufViewEffect` needed `ShaderComposer::Get().Compose()` to resolve `#include "debug/debug_print"`.
+  - Added per-tile labels to `gbuf_view.wgsl` via `debug_str`. Scale propagation for pulsating sphere confirmed correct end-to-end. 36/36 tests.
+
 - [x] **CNN v3 Phase 7: Validation tools** — `GBufViewEffect` (C++ 4×5 channel grid, `cnn_v3/shaders/gbuf_view.wgsl`, `cnn_v3/src/gbuf_view_effect.{h,cc}`): renders all 20 G-buffer feature channels tiled on screen; custom BGL with `WGPUTextureSampleType_Uint`, bind group rebuilt per frame via `wgpuRenderPipelineGetBindGroupLayout`. Web tool "Load sample directory" (`cnn_v3/tools/tester.js` + `shaders.js`): `webkitdirectory` picker, `FULL_PACK_SHADER` compute (matches `gbuf_pack.wgsl`), `runFromFeat()` inference, PSNR vs `target.png`. 36/36 tests.
 
 - [x] **CNN v3 Phase 5: Parity validation** — `test_cnn_v3_parity.cc` (2 tests: zero_weights, random_weights). Root cause: intermediate nodes declared at full res instead of W/2, W/4. Fix: `NodeRegistry::default_width()/default_height()` getters + fractional resolution in `declare_nodes()`. Final max_err=4.88e-4 ✓. 36/36 tests.