ci: make CUDA conditional lane GPU-capable

tests/test_conditional_gate_scripts.py

@@ -37,6 +37,18 @@ def test_committed_conditional_policy_is_complete():
     ) == []
 
 
+def test_cuda_job_replaces_locked_cpu_torch_with_same_version_cuda_build():
+    workflow = (ROOT / ".github" / "workflows" / "conditional-tests.yml").read_text()
+    cuda_job = workflow.split("  cuda:\n", maxsplit=1)[1].split("  mps:\n", maxsplit=1)[0]
+
+    assert "torch.__version__.split" in cuda_job
+    assert "UV_TORCH_BACKEND=cu130 uv pip install" in cuda_job
+    assert "--reinstall-package torch" in cuda_job
+    assert '"torch==$CUDA_TORCH_VERSION"' in cuda_job
+    assert "assert torch.version.cuda is not None" in cuda_job
+    assert 'uv pip check --python "$CONDITIONAL_ENV/bin/python"' in cuda_job
+
+
 def test_policy_rejects_unknown_cpu_exclusion_gate(tmp_path):
     policy = json.loads((ROOT / "ci" / "conditional-test-policy.json").read_text())
     quality = {