The load-bearing logic of a thing lives in exactly one tested place, and every consumer reads it identically. A second copy — or a fallback each consumer must remember to prefer — is a latent bug: sooner or later one consumer diverges and silently ships stale behavior.
The sharpest instance here: the linter and the fixer share one scanner, so the linter can never demand a rewrite the fixer wouldn’t make. Two implementations of “what counts as a bare reference” would drift within a month, and the failure mode is the worst kind — a CI failure whose suggested remedy doesn’t work.
The same reasoning rejected threading configuration through every entry point (ADR-006): the second caller forgets an argument, and the two checks quietly cover different files.
“The new thing overrides the old at one site” is the smell; “the new thing replaces the old everywhere” is the fix.