D008 - Unimplemented stubs refuse by default

Status: decided Date: 2026-08-19

An unimplemented function answers Unimplemented, never success. The stub policy is a runtime TOML file keyed by symbol name, so relaxing one function is an edit and a relaunch.

Why: a stub that reports success is indistinguishable from working code until the guest corrupts something much later. Editing the policy and relaunching is the bisection workflow, and it must not need a rebuild.

Rejected:

• Default success: plausible behaviour that hides the missing implementation.
• Policy compiled into the binary: every experiment becomes a rebuild.