docs: session handoff — CNN v3 Phase 4 complete

- TODO.md: mark Phase 4 done, add FiLM MLP training details (blocked on
  train_cnn_v3.py), clarify what 'real' set_film_params() requires
- COMPLETED.md: archive Phase 4 with alignment fix note (vec3u→64/96 bytes)

handoff(Gemini): next up CNN v3 Phase 5 (parity validation) or train_cnn_v3.py

1 files changed, 2 insertions, 0 deletions

diff --git a/doc/COMPLETED.md b/doc/COMPLETED.md
index 42e4bc6..6868484 100644
--- a/doc/COMPLETED.md
+++ b/doc/COMPLETED.md
@@ -36,6 +36,8 @@ Completed task archive. See `doc/archive/` for detailed historical documents.
 
 ## March 2026
 
+- [x] **CNN v3 Phase 4: C++ CNNv3Effect + FiLM uniform upload** — `cnn_v3/src/cnn_v3_effect.{h,cc}`. 5 compute passes (enc0→enc1→bottleneck→dec1→dec0), shared f16 weights buffer, per-pass uniform buffers, `set_film_params()` API. Key fix: WGSL `vec3u` has align=16, so `CnnV3Params4ch`=64B and `CnnV3ParamsEnc1`=96B (not 48/80). Weight offsets as explicit formulas. FiLM γ/β identity defaults; real values await `train_cnn_v3.py`. 35/35 tests.
+
 - [x] **NTSC post-process effect** — Fisheye distortion + NTSC scan-line simulation as `WgslEffect` thin wrappers. Common logic in `render/ntsc_common` snippet (`sample_ntsc_signal` hook). Two variants: `ntsc_rgb.wgsl` (RGB→YIQ internally, `Ntsc`) and `ntsc_yiq.wgsl` (YIQ passthrough, `NtscYiq`, for RotatingCube output). Files: `src/effects/ntsc_rgb.wgsl`, `ntsc_yiq.wgsl`, `src/shaders/render/ntsc_common.wgsl`, `ntsc_effect.h`. Tests: 36/36.
 
 - [x] **Scratch post-process effect** — Film-scratch overlay effect. Scratch logic extracted into reusable snippet `src/shaders/render/scratch_lines.wgsl` (`#include "render/scratch_lines"`). Applied to first two timeline sequences. Tests: 35/35.