Refactoring Surgeon

It comes loaded with Martin Fowler's refactoring catalog, knows the difference between bloaters and change preventers, and includes reference examples for patterns like strangler fig and extract method. The anti-patterns section alone is worth the read, especially "Refactoring Production During Incidents" which we've all been guilty of. It has read/write/edit access plus limited bash for running tests and linting. Pairs well with test-automation-expert since you should never refactor without a safety net. Think of it as the voice in your head saying "commit now, one thing at a time, run the tests again."