An immediate user message — joins the active loop, or (idle) wakes or
persists; a persist no agent memory can hold answers memory-unavailable.
A durable AGENT inbox notification. Owners best-effort persist it for the next host-started turn; non-owners record it for the host dispatch tick.
A system signal (ifActive/ifIdle deliver/persist/discard/wake); a persist
no agent memory can hold answers memory-unavailable.
A durable thread-state lane (snapshot/delta, cacheKey dedupe). Owner gates
can return principal-mismatch or persistence-forbidden, missing memory
returns memory-unavailable, and an unbranded agent marks successful
non-skipped responses as degraded: 'not-runtime-driven'.
A message persisted for the next host-started turn.