feat(cnn_v3): G-buffer phase 1 + training infrastructure

G-buffer (Phase 1):
- Add NodeTypes GBUF_ALBEDO/DEPTH32/R8/RGBA32UINT to NodeRegistry
- GBufferEffect: MRT raster pass (albedo+normal_mat+depth) + pack compute
- Shaders: gbuf_raster.wgsl (MRT), gbuf_pack.wgsl (feature packing, 32B/px)
- Shadow/SDF passes stubbed (placeholder textures), CMake integration deferred

Training infrastructure (Phase 2):
- blender_export.py: headless EXR export with all G-buffer render passes
- pack_blender_sample.py: EXR → per-channel PNGs (oct-normals, 1/z depth)
- pack_photo_sample.py: photo → zero-filled G-buffer sample layout

handoff(Gemini): G-buffer phases 3-5 remain (U-Net shaders, CNNv3Effect, parity)

2 files changed, 31 insertions, 1 deletions

diff --git a/src/gpu/sequence.cc b/src/gpu/sequence.cc
index 1e3be6c..91ca187 100644
--- a/src/gpu/sequence.cc
+++ b/src/gpu/sequence.cc
@@ -181,6 +181,30 @@ void NodeRegistry::create_texture(Node& node) {
     usage = (WGPUTextureUsage)(WGPUTextureUsage_StorageBinding |
                                WGPUTextureUsage_TextureBinding);
     break;
+  case NodeType::GBUF_ALBEDO:
+    format = WGPUTextureFormat_RGBA16Float;
+    usage = (WGPUTextureUsage)(WGPUTextureUsage_RenderAttachment |
+                               WGPUTextureUsage_TextureBinding |
+                               WGPUTextureUsage_StorageBinding |
+                               WGPUTextureUsage_CopySrc);
+    break;
+  case NodeType::GBUF_DEPTH32:
+    format = WGPUTextureFormat_Depth32Float;
+    usage = (WGPUTextureUsage)(WGPUTextureUsage_RenderAttachment |
+                               WGPUTextureUsage_TextureBinding |
+                               WGPUTextureUsage_CopySrc);
+    break;
+  case NodeType::GBUF_R8:
+    format = WGPUTextureFormat_RGBA8Unorm;
+    usage = (WGPUTextureUsage)(WGPUTextureUsage_StorageBinding |
+                               WGPUTextureUsage_TextureBinding |
+                               WGPUTextureUsage_RenderAttachment);
+    break;
+  case NodeType::GBUF_RGBA32UINT:
+    format = WGPUTextureFormat_RGBA32Uint;
+    usage = (WGPUTextureUsage)(WGPUTextureUsage_StorageBinding |
+                               WGPUTextureUsage_TextureBinding);
+    break;
   }
 
   WGPUTextureDescriptor desc = {};
@@ -201,7 +225,8 @@ void NodeRegistry::create_texture(Node& node) {
   view_desc.mipLevelCount = 1;
   view_desc.baseArrayLayer = 0;
   view_desc.arrayLayerCount = 1;
-  view_desc.aspect = (node.type == NodeType::DEPTH24)
+  view_desc.aspect = (node.type == NodeType::DEPTH24 ||
+                      node.type == NodeType::GBUF_DEPTH32)
                          ? WGPUTextureAspect_DepthOnly
                          : WGPUTextureAspect_All;
 
diff --git a/src/gpu/sequence.h b/src/gpu/sequence.h
index a515d1f..4592082 100644
--- a/src/gpu/sequence.h
+++ b/src/gpu/sequence.h
@@ -20,6 +20,11 @@ enum class NodeType {
   F16X8,
   DEPTH24,
   COMPUTE_F32,
+  // G-buffer types for CNN v3
+  GBUF_ALBEDO,    // rgba16float: RENDER_ATTACHMENT | TEXTURE_BINDING | STORAGE_BINDING | COPY_SRC
+  GBUF_DEPTH32,   // depth32float: RENDER_ATTACHMENT | TEXTURE_BINDING | COPY_SRC
+  GBUF_R8,        // rgba8unorm (4ch for compat): STORAGE_BINDING | TEXTURE_BINDING | RENDER_ATTACHMENT
+  GBUF_RGBA32UINT, // rgba32uint: STORAGE_BINDING | TEXTURE_BINDING
 };
 
 struct Node {