ctx.subagents.interrupt() stops one live continuable child's current turn
via Agent.cancel(cause, { keepInbox: true }) under either a human durable
parent address or an exact live ancestor Agent. Fire-and-return: admission
is synchronous, quiescence is not awaited. Pending inbox work, the
Activation, and published descendants are preserved; only a later waking
send resumes the parked FIFO queue. Absent, one-shot, and disposing
targets are accepted no-ops.
The new Host RPC subagent.interrupt calls only that primitive with user
authority — no catalog, history, persistence, or parent-registry lookup —
so a live child stays stoppable while its parent Agent is offline.
Refs #1535
subagents.history drops its session-query read: a live child serves its
in-memory events with the registry watermark snapshot, a cold child goes
through inspectServable with a detached fold, and the retired
SESSION_QUERY_* arms disappear while every wire face stays put. The
design note records the shared read source.