D009 - Placeholder error codes avoid the high bit

Status: decided Date: 2026-08-19

GuestError placeholders never set the high bit, which real platform error codes set.

Why: a placeholder leaking into guest-visible behaviour must be recognisable in a trace and in a fault address, not plausible. A placeholder used as a pointer faults at an address that names the placeholder.

Rejected:

• Real-looking error codes: a leaked stub reads as a genuine platform failure.