The broker, the supervisor and the manager each copy the grant map at
start. An Authority answers what an add-on may call right now, so a
later change can apply to the next call without a restart.
Add the interface, the Reason type and EffectiveSet, with a static
implementation over today's prefix map. Nothing uses it yet and
behavior does not change.
Assisted-by: Claude:claude-sonnet-5-5 go