Fix a failing test case

Scope

• Work on one concrete failing test at a time.
• Keep the repro small and isolated under tests/.
• Do not try to fix failures that are due to changing the source layout; add them to EXPECTED_FAILURE.md instead.
• If a failure is due to shifting line numbers or changed source content (literal tracebacks, linecache, etc.), add it to EXPECTED_FAILURE.md.

Workflow

1. Reproduce the failure

   • Re-run the failing test directly (use the narrowest command possible, e.g. uvx pytest tests/test_file.py -k "test_name").
   • Capture the exact error, traceback, and any assertion mismatch.

2. Identify the root cause

   • Inspect the failing code path and surrounding logic.
   • Map the failure back to the minimal incorrect behavior (state mismatch, wrong transform, missing edge case).
   • If needed, use the python-debug skill for pdb stepping or the python-monitoring-trace skill for a sys.monitoring trace.

3. Always add a minimal repro under tests/

   • Create a new test file or extend the most relevant existing test file.
   • Keep the input as small as possible while still reproducing the failure.
   • Prefer integration-style tests consistent with existing tests/ conventions.

4. Explain the cause

   • Summarize the bug in one or two sentences.
   • Point to the relevant code path and why it misbehaves.

5. Implement the fix

   • Apply the smallest change that makes the repro pass.
   • Avoid unrelated refactors or behavior changes.
   • Never change the cpython source to fix a test.
   • The goal is to transform python to a minimal form, so do not selectively disable that to fix the tests.

6. Re-run the test

   • Re-run the specific failing test and the new repro.
   • If it uncovers additional failures, summarize them and continue iterating.

7. Final verification

   • Run the full required test commands (cargo test and uvx pytest tests/).

Output expectations

• Provide a short cause explanation and the fix rationale.
• List the exact tests re-run and the results.
• If more failures appear, list them with a brief classification (ERROR/FAIL/TIMEOUT/CRASHED).