D479 - A differential runs against whichever reachable implementation is published

Status: decided Date: 2026-09-02

The differential check runs against any reachable, published implementation of the same interface, naming which one it used, rather than requiring the target's own documented ancestor specifically.

Why: the nearest lawful analogue is not always available to provision locally, and a differential record already has to name its source. Using a reachable implementation and citing it satisfies that obligation without blocking the check on an environment that cannot be provisioned.

Rejected:

• Requiring the exact documented ancestor implementation: correct in principle, but unavailable without an elevated environment or a large third-party download, which blocks the check entirely.