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/gpu/test_effect_base.cc b/src/tests/gpu/test_effect_base.cc
index 68aabe3..64e5fa4 100644
--- a/src/tests/gpu/test_effect_base.cc
+++ b/src/tests/gpu/test_effect_base.cc
@@ -164,9 +164,11 @@ static void test_sequence_render() {
   WGPUCommandBuffer commands = wgpuCommandEncoderFinish(encoder, nullptr);
   wgpuQueueSubmit(fixture.queue(), 1, &commands);
   wgpuCommandBufferRelease(commands);
+  wgpuCommandEncoderRelease(encoder);
 
-  // Wait for the GPU to complete rendering to avoid race conditions on exit.
-  wgpuDevicePoll(fixture.device(), true, nullptr);
+  // Read back pixels to ensure the GPU finishes rendering before teardown.
+  // This avoids intermittent crashes on shutdown.
+  target.read_pixels();
 
   fprintf(stdout, "  ✓ Sequence rendered without error\n");
 }