refactor(headless): convert nullptr checks to strippable macros

Added HEADLESS_RETURN_IF_NULL/HEADLESS_RETURN_VAL_IF_NULL macros
that compile to no-ops in STRIP_ALL/FINAL_STRIP modes.

Files updated:
- fatal_error.h: New headless check macros
- sequence.cc: NodeRegistry::create_texture
- post_process_helper.cc: Pipeline creation functions
- sampler_cache.h: SamplerCache::get_or_create
- bind_group_builder.h: Layout/group builders
- pipeline_builder.h: Shader and pipeline builders
- All effect constructors (7 files)

Headless tests passing. STRIP_ALL builds will have zero overhead.

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

1 files changed, 3 insertions, 4 deletions

diff --git a/src/gpu/sampler_cache.h b/src/gpu/sampler_cache.h
index b3fdb19..7d88109 100644
--- a/src/gpu/sampler_cache.h
+++ b/src/gpu/sampler_cache.h
@@ -9,6 +9,7 @@ struct WGPUSamplerImpl;
 typedef struct WGPUSamplerImpl* WGPUSampler;
 
 #include "platform/platform.h"
+#include "util/fatal_error.h"
 
 struct SamplerSpec {
   WGPUAddressMode u, v;
@@ -39,10 +40,8 @@ class SamplerCache {
   }
 
   WGPUSampler get_or_create(WGPUDevice device, const SamplerSpec& spec) {
-    // Headless mode: skip sampler creation
-    if (device == nullptr) {
-      return nullptr;
-    }
+    // Headless mode: skip sampler creation (compiled out in STRIP_ALL)
+    HEADLESS_RETURN_VAL_IF_NULL(device, nullptr);
 
     auto it = cache_.find(spec);
     if (it != cache_.end())