Refactoring

One question governs every move:

While this step is in flight, how do we get back to green — and once it lands, what stops it rotting again?

Reversible in flight, ratcheted once landed. The system stays releasable at every commit; a refactor that needs the trunk broken for a week is a rewrite wearing a disguise.

The sections below are constraints a good plan satisfies, not a template to recite: shape the plan around the specific situation, keep its steps concrete to the codebase at hand, and skip a constraint only when it genuinely does not apply. When the system is unfamiliar and the original author is gone, a comprehension phase precedes even the safety net — see references/comprehension.md.

One precondition, two halves