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>

6 files changed, 102 insertions, 8 deletions

diff --git a/src/gpu/bind_group_builder.h b/src/gpu/bind_group_builder.h
index 55b7291..3b25ba9 100644
--- a/src/gpu/bind_group_builder.h
+++ b/src/gpu/bind_group_builder.h
@@ -93,6 +93,10 @@ class BindGroupLayoutBuilder {
   }
 
   WGPUBindGroupLayout build(WGPUDevice device) {
+    // Headless mode: skip bind group layout creation
+    if (device == nullptr) {
+      return nullptr;
+    }
     WGPUBindGroupLayoutDescriptor desc{};
     desc.entryCount = entries_.size();
     desc.entries = entries_.data();
@@ -130,6 +134,10 @@ class BindGroupBuilder {
   }
 
   WGPUBindGroup build(WGPUDevice device, WGPUBindGroupLayout layout) {
+    // Headless mode: skip bind group creation
+    if (device == nullptr) {
+      return nullptr;
+    }
     WGPUBindGroupDescriptor desc{};
     desc.layout = layout;
     desc.entryCount = entries_.size();
diff --git a/src/gpu/headless_gpu.cc b/src/gpu/headless_gpu.cc
index c4de577..e6995b2 100644
--- a/src/gpu/headless_gpu.cc
+++ b/src/gpu/headless_gpu.cc
@@ -78,6 +78,57 @@ WGPUSurface gpu_get_surface() {
   return nullptr;
 }
 
+TextureWithView gpu_create_texture_2d(WGPUDevice device, uint32_t width,
+                                      uint32_t height, WGPUTextureFormat format,
+                                      WGPUTextureUsage usage,
+                                      uint32_t mip_levels) {
+  (void)device;
+  (void)width;
+  (void)height;
+  (void)format;
+  (void)usage;
+  (void)mip_levels;
+  return {nullptr, nullptr};
+}
+
+TextureWithView gpu_create_storage_texture_2d(WGPUDevice device, uint32_t width,
+                                              uint32_t height,
+                                              WGPUTextureFormat format) {
+  (void)device;
+  (void)width;
+  (void)height;
+  (void)format;
+  return {nullptr, nullptr};
+}
+
+TextureWithView gpu_create_post_process_texture(WGPUDevice device,
+                                                uint32_t width, uint32_t height,
+                                                WGPUTextureFormat format) {
+  (void)device;
+  (void)width;
+  (void)height;
+  (void)format;
+  return {nullptr, nullptr};
+}
+
+WGPUTextureView gpu_create_mip_view(WGPUTexture texture,
+                                    WGPUTextureFormat format,
+                                    uint32_t mip_level) {
+  (void)texture;
+  (void)format;
+  (void)mip_level;
+  return nullptr;
+}
+
+WGPUTextureView gpu_create_texture_view_2d(WGPUTexture texture,
+                                           WGPUTextureFormat format,
+                                           uint32_t mip_levels) {
+  (void)texture;
+  (void)format;
+  (void)mip_levels;
+  return nullptr;
+}
+
 #if !defined(STRIP_ALL)
 void gpu_simulate_until(float time, float bpm) {
   (void)time;
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_;
diff --git a/src/gpu/post_process_helper.cc b/src/gpu/post_process_helper.cc
index 5f2ff56..6026f6e 100644
--- a/src/gpu/post_process_helper.cc
+++ b/src/gpu/post_process_helper.cc
@@ -14,6 +14,11 @@
 WGPURenderPipeline create_post_process_pipeline(WGPUDevice device,
                                                 WGPUTextureFormat format,
                                                 const char* shader_code) {
+  // Headless mode: skip pipeline creation
+  if (device == nullptr) {
+    return nullptr;
+  }
+
   WGPUBindGroupLayout bgl =
       BindGroupLayoutBuilder()
           .sampler(PP_BINDING_SAMPLER, WGPUShaderStage_Fragment)
@@ -40,6 +45,11 @@ WGPURenderPipeline create_post_process_pipeline(WGPUDevice device,
 WGPURenderPipeline create_post_process_pipeline_simple(WGPUDevice device,
                                                        WGPUTextureFormat format,
                                                        const char* shader_code) {
+  // Headless mode: skip pipeline creation
+  if (device == nullptr) {
+    return nullptr;
+  }
+
   WGPUBindGroupLayout bgl =
       BindGroupLayoutBuilder()
           .sampler(PP_BINDING_SAMPLER, WGPUShaderStage_Fragment)
@@ -67,6 +77,11 @@ static GpuBuffer g_dummy_buffer = {nullptr, 0};
 void pp_update_bind_group(WGPUDevice device, WGPURenderPipeline pipeline,
                           WGPUBindGroup* bind_group, WGPUTextureView input_view,
                           GpuBuffer uniforms, GpuBuffer effect_params) {
+  // Headless mode: skip bind group creation
+  if (device == nullptr || pipeline == nullptr) {
+    return;
+  }
+
   if (!g_dummy_buffer.buffer) {
     g_dummy_buffer = gpu_create_buffer(device, 32, WGPUBufferUsage_Uniform);
   }
diff --git a/src/gpu/sampler_cache.h b/src/gpu/sampler_cache.h
index 7149921..b3fdb19 100644
--- a/src/gpu/sampler_cache.h
+++ b/src/gpu/sampler_cache.h
@@ -39,6 +39,11 @@ class SamplerCache {
   }
 
   WGPUSampler get_or_create(WGPUDevice device, const SamplerSpec& spec) {
+    // Headless mode: skip sampler creation
+    if (device == nullptr) {
+      return nullptr;
+    }
+
     auto it = cache_.find(spec);
     if (it != cache_.end())
       return it->second;
diff --git a/src/gpu/sequence.cc b/src/gpu/sequence.cc
index 38a6866..578fc01 100644
--- a/src/gpu/sequence.cc
+++ b/src/gpu/sequence.cc
@@ -130,6 +130,13 @@ void NodeRegistry::set_external_view(const std::string& name,
 }
 
 void NodeRegistry::create_texture(Node& node) {
+  // Headless mode: skip texture creation
+  if (device_ == nullptr) {
+    node.texture = nullptr;
+    node.view = nullptr;
+    return;
+  }
+
   WGPUTextureFormat format;
   WGPUTextureUsage usage;