test: fix test_effect_base intermittent crashes and SIGTRAP

- Fix stack-use-after-scope dangling reference by storing mutable GpuContext in WebGPUTestFixture.

- Fix wgpuDevicePoll causing SIGTRAP and replace with target.read_pixels() to block for GPU teardown safely.

- Fix WGPUCommandEncoder leak.

1 files changed, 4 insertions, 2 deletions

diff --git a/src/tests/common/webgpu_test_fixture.h b/src/tests/common/webgpu_test_fixture.h
index e10a2ed..fa23587 100644
--- a/src/tests/common/webgpu_test_fixture.h
+++ b/src/tests/common/webgpu_test_fixture.h
@@ -34,8 +34,9 @@ class WebGPUTestFixture {
   WGPUTextureFormat format() const {
     return WGPUTextureFormat_BGRA8Unorm;
   }
-  GpuContext ctx() const {
-    return {device_, queue_, format()};
+  const GpuContext& ctx() const {
+    ctx_ = {device_, queue_, format()};
+    return ctx_;
   }
 
   // Check if fixture is ready
@@ -48,6 +49,7 @@ class WebGPUTestFixture {
   WGPUAdapter adapter_ = nullptr;
   WGPUDevice device_ = nullptr;
   WGPUQueue queue_ = nullptr;
+  mutable GpuContext ctx_ = {};
 
   // Callback state for async device request
   struct RequestState {