fix(headless): add nullptr checks for GPU resource creation

- NodeRegistry::create_texture: skip texture creation when device is nullptr
- Post-process helpers: skip pipeline/bind group creation in headless mode
- SamplerCache: return nullptr for headless mode
- BindGroupLayoutBuilder/BindGroupBuilder: skip creation with null device
- RenderPipelineBuilder: skip shader module and pipeline creation in headless
- PlaceholderEffect: skip sampler creation in headless mode
- RotatingCubeEffect: early return in constructor for headless mode

WIP: Some effects (GaussianBlur, etc.) still need headless checks

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

1 files changed, 16 insertions, 8 deletions

diff --git a/src/gpu/pipeline_builder.h b/src/gpu/pipeline_builder.h
index 87b9190..a258b49 100644
--- a/src/gpu/pipeline_builder.h
+++ b/src/gpu/pipeline_builder.h
@@ -38,14 +38,17 @@ class RenderPipelineBuilder {
 
   RenderPipelineBuilder& shader(const char* wgsl, bool compose = true) {
     shader_text_ = compose ? ShaderComposer::Get().Compose({}, wgsl) : wgsl;
-    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");
+    // Headless mode: skip shader module creation
+    if (device_ != nullptr) {
+      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;
   }
 
@@ -85,6 +88,11 @@ class RenderPipelineBuilder {
   }
 
   WGPURenderPipeline build() {
+    // Headless mode: skip pipeline creation
+    if (device_ == nullptr) {
+      return nullptr;
+    }
+
     color_.writeMask = WGPUColorWriteMask_All;
     if (has_blend_)
       color_.blend = &blend_;