Issue: #

Requirements for PR author:

• [ ] All missing test coverage is tracked with “TODO” or .unimplemented().
• [ ] New helpers are /** documented */ and new helper files are found in helper_index.txt.
• [ ] Test behaves as expected in a WebGPU implementation. (If not passing, explain above.)
• [ ] Test have be tested with compatibility mode validation enabled and behave as expected. (If not passing, explain above.)

Requirements for reviewer sign-off:

• [ ] Tests are properly located.
• [ ] Test descriptions are accurate and complete.
• [ ] Tests provide complete coverage (including validation control cases). Missing coverage MUST be covered by TODOs.
• [ ] Tests avoid over-parameterization (see case count report).

When landing this PR, be sure to make any necessary issue status updates.