An additive, behavior-neutral callback. A buffered async message
(Received.isMessage — a pushed event from a provider this service
subscribed to) carries a payload in the receive buffer; run() now hands
it to on_buffered_message before falling through to on_notification with
the badge, so a coalesced timer/exit riding the same wake is not lost. A
service that does not set the callback (all of them today) is unchanged:
the isMessage branch is a no-op and on_notification still runs, exactly
as before.
This is the seam the volume manager needs to consume block
medium_changed: the event's reserved op number collides with the volume
manager's own hello, so it must be decoded by hand here, never through
the protocol dispatch. Full suite neutral (the lone device-authority
miss is a known child-cleanup race that passes on rerun).
Daniel Samson
0faa0fd21b