refactor(gpu): move RenderPipelineBuilder impl to pipeline_builder.cc

Keeps .h as declarations only; moves all method bodies to .cc.
Adds pipeline_builder.cc to COMMON_GPU_EFFECTS in DemoSourceLists.cmake.

handoff(Claude): pipeline_builder split to .h/.cc, builds clean.

2 files changed, 100 insertions, 90 deletions

diff --git a/src/gpu/pipeline_builder.cc b/src/gpu/pipeline_builder.cc
new file mode 100644
index 0000000..b3fa5f8
--- /dev/null
+++ b/src/gpu/pipeline_builder.cc
@@ -0,0 +1,91 @@
+// WGPU render pipeline builder - implementation
+#include "gpu/pipeline_builder.h"
+#include "util/fatal_error.h"
+
+RenderPipelineBuilder::RenderPipelineBuilder(WGPUDevice device)
+    : device_(device) {
+  desc_.primitive.topology = WGPUPrimitiveTopology_TriangleList;
+  desc_.primitive.cullMode = WGPUCullMode_None;
+  desc_.multisample.count = 1;
+  desc_.multisample.mask = 0xFFFFFFFF;
+}
+
+RenderPipelineBuilder& RenderPipelineBuilder::shader(const char* wgsl,
+                                                      bool compose) {
+  shader_text_ = compose ? ShaderComposer::Get().Compose({}, wgsl) : wgsl;
+  if (device_ == nullptr)
+    return *this;
+  WGPUShaderSourceWGSL wgsl_src{};
+  wgsl_src.chain.sType = WGPUSType_ShaderSourceWGSL;
+  wgsl_src.code = str_view(shader_text_.c_str());
+  WGPUShaderModuleDescriptor shader_desc{};
+  shader_desc.nextInChain = &wgsl_src.chain;
+  shader_module_ = wgpuDeviceCreateShaderModule(device_, &shader_desc);
+  desc_.vertex.module = shader_module_;
+  desc_.vertex.entryPoint = str_view("vs_main");
+  return *this;
+}
+
+RenderPipelineBuilder& RenderPipelineBuilder::bind_group_layout(
+    WGPUBindGroupLayout layout) {
+  layouts_.push_back(layout);
+  return *this;
+}
+
+RenderPipelineBuilder& RenderPipelineBuilder::format(WGPUTextureFormat fmt) {
+  color_.format = fmt;
+  return *this;
+}
+
+RenderPipelineBuilder& RenderPipelineBuilder::blend_alpha() {
+  has_blend_ = true;
+  blend_.color.operation = WGPUBlendOperation_Add;
+  blend_.color.srcFactor = WGPUBlendFactor_SrcAlpha;
+  blend_.color.dstFactor = WGPUBlendFactor_OneMinusSrcAlpha;
+  blend_.alpha.operation = WGPUBlendOperation_Add;
+  blend_.alpha.srcFactor = WGPUBlendFactor_One;
+  blend_.alpha.dstFactor = WGPUBlendFactor_OneMinusSrcAlpha;
+  return *this;
+}
+
+RenderPipelineBuilder& RenderPipelineBuilder::depth(
+    WGPUTextureFormat depth_fmt) {
+  has_depth_ = true;
+  depth_.format = depth_fmt;
+  depth_.depthWriteEnabled = WGPUOptionalBool_True;
+  depth_.depthCompare = WGPUCompareFunction_Less;
+  return *this;
+}
+
+RenderPipelineBuilder& RenderPipelineBuilder::cull_back() {
+  desc_.primitive.cullMode = WGPUCullMode_Back;
+  return *this;
+}
+
+WGPURenderPipeline RenderPipelineBuilder::build() {
+  HEADLESS_RETURN_VAL_IF_NULL(device_, nullptr);
+
+  color_.writeMask = WGPUColorWriteMask_All;
+  if (has_blend_)
+    color_.blend = &blend_;
+
+  WGPUFragmentState fragment{};
+  fragment.module = shader_module_;
+  fragment.entryPoint = str_view("fs_main");
+  fragment.targetCount = 1;
+  fragment.targets = &color_;
+
+  WGPUPipelineLayoutDescriptor pl_desc{};
+  pl_desc.bindGroupLayoutCount = layouts_.size();
+  pl_desc.bindGroupLayouts = layouts_.data();
+  WGPUPipelineLayout layout = wgpuDeviceCreatePipelineLayout(device_, &pl_desc);
+
+  desc_.layout = layout;
+  desc_.fragment = &fragment;
+  if (has_depth_)
+    desc_.depthStencil = &depth_;
+
+  WGPURenderPipeline pipeline = wgpuDeviceCreateRenderPipeline(device_, &desc_);
+  wgpuPipelineLayoutRelease(layout);
+  return pipeline;
+}
diff --git a/src/gpu/pipeline_builder.h b/src/gpu/pipeline_builder.h
index 937c55f..9fd76f9 100644
--- a/src/gpu/pipeline_builder.h
+++ b/src/gpu/pipeline_builder.h
@@ -3,7 +3,6 @@
 #include <string>
 #include <vector>
 
-// Forward declarations (users must include gpu.h and shader_composer.h)
 struct WGPUDeviceImpl;
 typedef struct WGPUDeviceImpl* WGPUDevice;
 struct WGPUBindGroupLayoutImpl;
@@ -15,7 +14,6 @@ typedef struct WGPUShaderModuleImpl* WGPUShaderModule;
 
 #include "gpu/shader_composer.h"
 #include "platform/platform.h"
-#include "util/fatal_error.h"
 
 class RenderPipelineBuilder {
   WGPUDevice device_;
@@ -30,93 +28,14 @@ class RenderPipelineBuilder {
   bool has_depth_ = false;
 
  public:
-  explicit RenderPipelineBuilder(WGPUDevice device) : device_(device) {
-    desc_.primitive.topology = WGPUPrimitiveTopology_TriangleList;
-    desc_.primitive.cullMode = WGPUCullMode_None;
-    desc_.multisample.count = 1;
-    desc_.multisample.mask = 0xFFFFFFFF;
-  }
+  explicit RenderPipelineBuilder(WGPUDevice device);
 
-  RenderPipelineBuilder& shader(const char* wgsl, bool compose = true) {
-    shader_text_ = compose ? ShaderComposer::Get().Compose({}, wgsl) : wgsl;
-    // Headless mode: skip shader module creation (compiled out in STRIP_ALL)
-    if (device_ == nullptr) {
-      return *this;
-    }
-    WGPUShaderSourceWGSL wgsl_src{};
-    wgsl_src.chain.sType = WGPUSType_ShaderSourceWGSL;
-    wgsl_src.code = str_view(shader_text_.c_str());
-    WGPUShaderModuleDescriptor shader_desc{};
-    shader_desc.nextInChain = &wgsl_src.chain;
-    shader_module_ = wgpuDeviceCreateShaderModule(device_, &shader_desc);
-    desc_.vertex.module = shader_module_;
-    desc_.vertex.entryPoint = str_view("vs_main");
-    return *this;
-  }
-
-  RenderPipelineBuilder& bind_group_layout(WGPUBindGroupLayout layout) {
-    layouts_.push_back(layout);
-    return *this;
-  }
-
-  RenderPipelineBuilder& format(WGPUTextureFormat fmt) {
-    color_.format = fmt;
-    return *this;
-  }
-
-  RenderPipelineBuilder& blend_alpha() {
-    has_blend_ = true;
-    blend_.color.operation = WGPUBlendOperation_Add;
-    blend_.color.srcFactor = WGPUBlendFactor_SrcAlpha;
-    blend_.color.dstFactor = WGPUBlendFactor_OneMinusSrcAlpha;
-    blend_.alpha.operation = WGPUBlendOperation_Add;
-    blend_.alpha.srcFactor = WGPUBlendFactor_One;
-    blend_.alpha.dstFactor = WGPUBlendFactor_OneMinusSrcAlpha;
-    return *this;
-  }
-
-  RenderPipelineBuilder&
-  depth(WGPUTextureFormat depth_fmt = WGPUTextureFormat_Depth24Plus) {
-    has_depth_ = true;
-    depth_.format = depth_fmt;
-    depth_.depthWriteEnabled = WGPUOptionalBool_True;
-    depth_.depthCompare = WGPUCompareFunction_Less;
-    return *this;
-  }
-
-  RenderPipelineBuilder& cull_back() {
-    desc_.primitive.cullMode = WGPUCullMode_Back;
-    return *this;
-  }
-
-  WGPURenderPipeline build() {
-    // Headless mode: skip pipeline creation (compiled out in STRIP_ALL)
-    HEADLESS_RETURN_VAL_IF_NULL(device_, nullptr);
-
-    color_.writeMask = WGPUColorWriteMask_All;
-    if (has_blend_)
-      color_.blend = &blend_;
-
-    WGPUFragmentState fragment{};
-    fragment.module = shader_module_;
-    fragment.entryPoint = str_view("fs_main");
-    fragment.targetCount = 1;
-    fragment.targets = &color_;
-
-    WGPUPipelineLayoutDescriptor pl_desc{};
-    pl_desc.bindGroupLayoutCount = layouts_.size();
-    pl_desc.bindGroupLayouts = layouts_.data();
-    WGPUPipelineLayout layout =
-        wgpuDeviceCreatePipelineLayout(device_, &pl_desc);
-
-    desc_.layout = layout;
-    desc_.fragment = &fragment;
-    if (has_depth_)
-      desc_.depthStencil = &depth_;
-
-    WGPURenderPipeline pipeline =
-        wgpuDeviceCreateRenderPipeline(device_, &desc_);
-    wgpuPipelineLayoutRelease(layout);
-    return pipeline;
-  }
+  RenderPipelineBuilder& shader(const char* wgsl, bool compose = true);
+  RenderPipelineBuilder& bind_group_layout(WGPUBindGroupLayout layout);
+  RenderPipelineBuilder& format(WGPUTextureFormat fmt);
+  RenderPipelineBuilder& blend_alpha();
+  RenderPipelineBuilder& depth(
+      WGPUTextureFormat depth_fmt = WGPUTextureFormat_Depth24Plus);
+  RenderPipelineBuilder& cull_back();
+  WGPURenderPipeline build();
 };