- listChildren() takes an optional AbortSignal and rechecks it after every
un-signalled session-query await (the cold-resume cooperative-cancellation
boundary); list_agents forwards exec.signal so the registry's drain of
started tool bodies cannot block on a slow or large catalog.
- The list_agents description now presents running/complete as a stored-record
snapshot and defers deliverability to send_message, matching the ownership-
conflict semantics the service tests pin.
Implements the durable-subagent-catalog RFC: SubagentControlService.listChildren()
enumerates a parent's direct continuable children from one sessionQuery trace,
validates each child's sole subagent/descriptor event (now carrying the durable
creation label), and returns one ordered SubagentListEntry[] with per-child
corrupt/unsupported/unavailable diagnostics. The list_agents tool ships as a
separately loadable plugin of dsh-tool-subagent-control requiring sessionQuery
at load; send_message stays usable without it.