fix: CNN test tool GPU readback with wgpuDevicePoll

Fixed buffer mapping callback mode mismatch causing Unknown status.
Changed from WaitAnyOnly+ProcessEvents to AllowProcessEvents+DevicePoll.

Readback now functional but CNN output incorrect (all white).
Issue isolated to tool-specific binding/uniform setup - CNNEffect
in demo works correctly.

Technical details:
- WGPUCallbackMode_WaitAnyOnly requires wgpuInstanceWaitAny
- Using wgpuInstanceProcessEvents with WaitAnyOnly never fires callback
- Fixed by using AllowProcessEvents mode + wgpuDevicePoll
- Removed debug output and platform warnings

Status: 36/36 tests pass, readback works, CNN shader issue remains.

handoff(Claude): CNN test tool readback fixed, output debugging needed

1 files changed, 2 insertions, 2 deletions

diff --git a/PROJECT_CONTEXT.md b/PROJECT_CONTEXT.md
index 8b84cde..7e8107e 100644
--- a/PROJECT_CONTEXT.md
+++ b/PROJECT_CONTEXT.md
@@ -35,8 +35,8 @@
 - **Audio:** Sample-accurate sync. Zero heap allocations per frame. Variable tempo. Comprehensive tests.
 - **Shaders:** Parameterized effects (UniformHelper, .seq syntax). Modular WGSL composition.
 - **3D:** Hybrid SDF/rasterization with BVH. Binary scene loader. Blender pipeline.
-- **Effects:** CNN post-processing foundation (3-layer architecture, modular snippets, validation tool).
-- **Tools:** CNN test tool for offline shader validation. Texture readback utility for GPU-to-CPU operations.
+- **Effects:** CNN post-processing foundation (3-layer architecture, modular snippets). CNNEffect validated in demo.
+- **Tools:** CNN test tool (readback works, output incorrect - under investigation). Texture readback utility functional.
 - **Build:** Asset dependency tracking. Size measurement. Hot-reload (debug-only).
 - **Testing:** **36/36 passing (100%)**