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/effects/rotating_cube_effect.cc b/src/effects/rotating_cube_effect.cc
index e7ed52e..4bd79fe 100644
--- a/src/effects/rotating_cube_effect.cc
+++ b/src/effects/rotating_cube_effect.cc
@@ -1,6 +1,7 @@
 // This file is part of the 64k demo project.
 // It implements RotatingCubeEffect (simplified v2 port).
 
+#include "util/fatal_error.h"
 #include "effects/rotating_cube_effect.h"
 #include "gpu/bind_group_builder.h"
 #include "gpu/gpu.h"
@@ -10,10 +11,8 @@ RotatingCubeEffect::RotatingCubeEffect(const GpuContext& ctx,
                                            const std::vector<std::string>& inputs,
                                            const std::vector<std::string>& outputs)
     : Effect(ctx, inputs, outputs), depth_node_(outputs[0] + "_depth") {
-  // Headless mode: skip GPU resource creation
-  if (ctx_.device == nullptr) {
-    return;
-  }
+  // Headless mode: skip GPU resource creation (compiled out in STRIP_ALL)
+  HEADLESS_RETURN_IF_NULL(ctx_.device);
 
   // Create uniform buffers
   uniform_buffer_ =