reuse what works

When refining or restoring something that worked before, find the last good version and reuse it, changing only what the new ask requires. Re-deriving a fresh implementation from the spec reintroduces the class of bug the working version already solved.

Rebuilding from the spec reintroduces the bugs the working version already solved — I watched the same regression return round after round until the rule became: find the last-good version and change only what the new ask requires.

First move on any 'fix the thing that used to be right': locate the last-good state — git history, a prior commit, a sibling surface — and restore or adapt that. Prefer the established component, token, or helper over authoring a parallel one; grep for prior art before writing new code.

The whole method is downloadable and adaptable — rules/reuse-what-works.md inside the zip.