feat(cnn_v3): Phase 4 complete — CNNv3Effect C++ + FiLM uniform upload

- cnn_v3/src/cnn_v3_effect.{h,cc}: full Effect subclass with 5 compute
  passes (enc0→enc1→bottleneck→dec1→dec0), shared weights storage buffer,
  per-pass uniform buffers, set_film_params() API
- Fixed WGSL/C++ struct alignment: vec3u has align=16, so CnnV3Params4ch
  is 64 bytes and CnnV3ParamsEnc1 is 96 bytes (not 48/80)
- Weight offsets computed as explicit formulas (e.g. 20*4*9+4) for clarity
- Registered in CMake, shaders.h/cc, demo_effects.h, test_demo_effects.cc
- 35/35 tests pass

handoff(Gemini): CNN v3 Phase 5 next — parity validation (Python ref vs WGSL)

1 files changed, 2 insertions, 2 deletions

diff --git a/PROJECT_CONTEXT.md b/PROJECT_CONTEXT.md
index f42ccf4..4767185 100644
--- a/PROJECT_CONTEXT.md
+++ b/PROJECT_CONTEXT.md
@@ -36,7 +36,7 @@
 - **Audio:** Sample-accurate sync. Zero heap allocations per frame. Variable tempo. OLA-IDCT synthesis (v2 .spec): Hann analysis window, rectangular synthesis, 50% overlap, click-free. V1 (raw DCT-512) preserved for generated notes. .spec files regenerated as v2.
 - **Shaders:** Parameterized effects (UniformHelper, .seq syntax). Beat-synchronized animation support (`beat_time`, `beat_phase`). Modular WGSL composition with ShaderComposer. 27 shared common shaders (math, render, compute). Reusable snippets: `render/scratch_lines`, `render/ntsc_common` (NTSC signal processing, RGB and YIQ input variants via `sample_ntsc_signal` hook), `math/color` (YIQ/NTSC), `math/color_c64` (C64 palette, Bayer dither, border animation).
 - **3D:** Hybrid SDF/rasterization with BVH. Binary scene loader. Blender pipeline.
-- **Effects:** CNN post-processing: CNNEffect (v1) and CNNv2Effect operational. CNN v2: sigmoid activation, storage buffer weights (~3.2 KB), 7D static features, dynamic layers. Training stable, convergence validated. **CNN v3 Phase 3 complete:** 5 WGSL inference shaders (enc0/enc1/bottleneck/dec1/dec0) + `cnn_v3/common` snippet. Zero-pad convs, AvgPool down, NearestUp, FiLM, skip-concat, sigmoid output. Registered in assets + shaders.cc. See `cnn_v3/docs/HOWTO.md` §7.
+- **Effects:** CNN post-processing: CNNEffect (v1) and CNNv2Effect operational. CNN v2: sigmoid activation, storage buffer weights (~3.2 KB), 7D static features, dynamic layers. Training stable, convergence validated. **CNN v3 Phase 4 complete:** `CNNv3Effect` C++ class (5 compute passes, FiLM uniform upload, identity γ/β defaults). `set_film_params()` modulates all layers via beat/audio. WGSL params struct alignment fix (vec3u align=16 → 64/96-byte C++ mirrors). Registered in CMake, shaders.h/cc, demo_effects.h, tests. See `cnn_v3/docs/HOWTO.md`.
 - **Tools:** CNN test tool operational. Texture readback utility functional. Timeline editor (web-based, beat-aligned, audio playback).
 - **Build:** Asset dependency tracking. Size measurement. Hot-reload (debug-only). WSL (Windows 10) supported: native Linux build and cross-compile to `.exe` via `mingw-w64`.
 - **Sequence:** DAG-based effect routing with explicit node system. Python compiler with topological sort and ping-pong optimization. 12 effects operational (Passthrough, Placeholder, GaussianBlur, Heptagon, Particles, RotatingCube, Hybrid3D, Flash, PeakMeter, Scene1, Scene2, Scratch). Effect times are absolute (seq_compiler adds sequence start offset). See `doc/SEQUENCE.md`.
@@ -46,7 +46,7 @@
 
 ## Next Up
 
-**Active:** CNN v3 Phase 4 (C++ CNNv3Effect + FiLM uniform), Spectral Brush Editor
+**Active:** CNN v3 Phase 5 (parity validation), Spectral Brush Editor
 **Ongoing:** Test infrastructure maintenance (35/35 passing)
 **Future:** Size optimization (64k target), 3D enhancements