D399 - A diagnostic that varies an entry condition must declare which one

Status: decided Date: 2026-08-30

A tool that changes what a guest is entered with (for example, which structure or argument convention its entry point receives) must select that convention explicitly rather than assuming a single fixed one, and every setting that can change a run's behavior is registered wherever this project checks whether a run was ordinary.

Why: An instrument that poisons one input and assumes every other input is some fixed shape draws a false "nothing reached" conclusion when the guest was never given that shape to begin with. A setting missing from the ordinary-run registry lets an intervened run silently report itself as unremarkable, which has happened before.

Rejected:

• One fixed entry convention for every diagnostic: correct for one guest shape and silently wrong for every other.