fix(headless): add missing sampler/texture stubs to gpu_headless.cc

gpu_create_linear_sampler, gpu_create_nearest_sampler, and
gpu_create_dummy_scene_texture were defined only in gpu.cc, causing
link errors in DEMO_HEADLESS mode.

handoff(Gemini): headless mode link error fixed, 35/35 tests should still pass.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

1 files changed, 15 insertions, 0 deletions

diff --git a/src/gpu/gpu_headless.cc b/src/gpu/gpu_headless.cc
index e6995b2..547ca18 100644
--- a/src/gpu/gpu_headless.cc
+++ b/src/gpu/gpu_headless.cc
@@ -129,6 +129,21 @@ WGPUTextureView gpu_create_texture_view_2d(WGPUTexture texture,
   return nullptr;
 }
 
+WGPUSampler gpu_create_linear_sampler(WGPUDevice device) {
+  (void)device;
+  return nullptr;
+}
+
+WGPUSampler gpu_create_nearest_sampler(WGPUDevice device) {
+  (void)device;
+  return nullptr;
+}
+
+TextureWithView gpu_create_dummy_scene_texture(WGPUDevice device) {
+  (void)device;
+  return {nullptr, nullptr};
+}
+
 #if !defined(STRIP_ALL)
 void gpu_simulate_until(float time, float bpm) {
   (void)time;