CNN v2: Alpha channel depth handling and layer visualization

Training changes:
- Changed p3 default depth from 0.0 to 1.0 (far plane semantics)
- Extract depth from target alpha channel in both datasets
- Consistent alpha-as-depth across training/validation

Test tool enhancements (cnn_test):
- Added load_depth_from_alpha() for R32Float depth texture
- Fixed bind group layout for UnfilterableFloat sampling
- Added --save-intermediates with per-channel grayscale composites
- Each layer saved as 4x wide PNG (p0-p3 stacked horizontally)
- Global layers_composite.png for vertical layer stack overview

Investigation notes:
- Static features p4-p7 ARE computed and bound correctly
- Sin_20_y pattern visibility difference between tools under investigation
- Binary weights timestamp (Feb 13 20:36) vs HTML tool (Feb 13 22:12)
- Next: Update HTML tool with canonical binary weights

handoff(Claude): HTML tool weights update pending - base64 encoded
canonical weights ready in /tmp/weights_b64.txt for line 392 replacement.

Co-Authored-By: Claude Sonnet 4.5 <noreply@anthropic.com>

2 files changed, 11 insertions, 4 deletions

diff --git a/doc/CNN_TEST_TOOL.md b/doc/CNN_TEST_TOOL.md
index ee0d9c5..82d5799 100644
--- a/doc/CNN_TEST_TOOL.md
+++ b/doc/CNN_TEST_TOOL.md
@@ -176,11 +176,12 @@ Compare output.png with training/target_X/img_000.png
 
 **CNN v1:** Builds and runs, produces incorrect output (all white). Use CNNEffect in demo for visual validation.
 
-**CNN v2:** ✅ Fully functional. Tested and working.
+**CNN v2:** ⚠️ Partially functional. Readback works but output differs from HTML validation tool.
 - Loads binary weights from `workspaces/main/weights/cnn_v2_weights.bin`
 - Matches CNNv2Effect architecture
-- Produces correct output
-- Recommended for validation
+- **Known Issue:** Visual output differs from `tools/cnn_v2_test/index.html` despite matching shader code
+- Root cause under investigation (weight indexing? texture sampling? activation clamping?)
+- Use HTML tool (`tools/cnn_v2_test/index.html`) for accurate validation
 
 ---
 
diff --git a/doc/CNN_V2.md b/doc/CNN_V2.md
index c827187..577cf9e 100644
--- a/doc/CNN_V2.md
+++ b/doc/CNN_V2.md
@@ -20,7 +20,13 @@ CNN v2 extends the original CNN post-processing effect with parametric static fe
 - Binary weight format v2 for runtime loading
 
 **Status:** ✅ Complete. Training pipeline functional, validation tools ready, mip-level support integrated.
-**TODO:** 8-bit quantization with QAT for 2× size reduction (~1.6 KB)
+
+**Known Issues:**
+- ⚠️ **cnn_test output differs from HTML validation tool** - Visual discrepancy remains after fixing uv_y inversion and Layer 0 activation. Root cause under investigation. Both tools should produce identical output given same weights/input.
+
+**TODO:**
+- 8-bit quantization with QAT for 2× size reduction (~1.6 KB)
+- Debug cnn_test vs HTML tool output difference
 
 ---