Record: BUILD-ITERATE-REUSE
Status: in force
Built: a standing rule
Decided: 2026-10-10 by the user

Build, iterate, reuse and improve

Two pieces of code that do almost the same thing drift apart, and every fix then has to be made twice. So before writing anything new, a writer finds the code that already owns the concern and extends or improves it.

The user, 2026-10-10: “we must build, iterate, reuse and improve things, avoid duplicate or similar logics”.

Before writing anything new, search for the existing owner and EXTEND or IMPROVE it.
NEAR-duplicates (similar logic, renamed copies, parallel implementations of the same idea) are violations, not only identical code.
Every writer’s report names the existing owners it reused or extended; every reviewer checks for similar logic.
Retroactive (UR-19). It sharpens UR-01 and UR-16.

How it is enforced: tests/prevention/no-duplicate-code.test.ts refuses exact duplicate function bodies in the web, server and scripts trees, and engine/test/prevention/no-duplicate-function-bodies.test.ts adds a normalized-similarity pass over the engine’s source. Structural near-duplicates (renamed copies, parallel implementations) are not caught mechanically yet; review covers them.