Fix the injected bug in /testbed. The source tree is the only thing scored.

Score: the share of hidden checks that pass against the source tree at /testbed when the episode ends. Zero-regression rule: if any check that passed before now fails, the episode scores zero regardless of what was fixed. Budget: 30 minutes, 100 tool turns, 600,000 tokens.

1. Read the issue. List its named symbols, symptoms, and expected outputs. Each is one site to fix — these bugs often carry several.
2. search_files the first symbol. Read the function it lives in and the surviving tests that exercise it — they show the intended behavior.
3. By your tenth tool call, apply your best-candidate fix. A fix you later refine costs nothing; an unfixed tree scores zero.
4. Fix every remaining symptom. Check the whole function for the same pattern twice (swapped pairs, dropped guards, twisted expressions).
5. Prove it: run the issue's snippet in /tmp and confirm the output matches exactly. A passing exit code is not proof — the output is.
6. Run the tests nearest each fix. If a passing test now fails, narrow or undo your edit.
7. Make the smallest edit that restores the described behavior. No refactors, no renames, no drive-by fixes. Do not "correct" a line next to the bug.
8. If a test fails with ModuleNotFoundError: never install anything. Prove the fix with the issue's snippet and the tests that DO import. One install attempt scores zero for the whole episode.
9. Never touch test files, test data, conftest.py, pytest.ini, tox.ini, setup.cfg, pyproject.toml, or any test-runner config. No network, no pip, no URLs. Write only inside /testbed (scratch in /tmp). No pytest.main, _pytest, importlib.machinery, sys.meta_path, sitecustomize, or .pth in source. No git commands except git diff and git checkout --.
10. Stop when the repro and the nearest tests pass. Time-outs are not failures: the checks you already fixed still count.

Check every branch against what its condition promises. Check whether two paired names (open/close, start/end, min/max) are used swapped. A fresh docstring on a rewritten function describes the ORIGINAL behavior — treat it as the spec. Compare with the sibling implementation. Exact strings, output order, and tuple shape are contracts. Fix the general rule, not the visible example.