One thing for everything

“The one thing for everything is a principle that must apply everywhere” (user, 2026-10-07). Every concern has exactly ONE implementation that everything else uses: one parser per format, one store per kind of data (no second copy of content: references, not copies), one process launcher and supervisor, one HTTP client, one logger, one settings reader, one approval primitive, one scope model, one serializer per format, one test runner door, one build and toolchain per language.

• Never introduce a second implementation “for now”, never defer consolidation, never ship a dual path.
• A task that touches a concern with duplicates consolidates them onto the one owner and deletes the rest in the same change.
• An exception must be proven necessary (code that physically runs in the browser, a declared test-only oracle) and still shares the single source of its definitions.

It sharpens UR-01 and UR-04, applies to every existing owner as well as new code (UR-19), and is enforced by mechanical guards, never by vigilance alone (UR-18).