Get a synthetic tool

Each step carries read-only connection_state, computed on read: ok (the connection exists and the caller can see it; connection_name is its display name), missing (the connection was deleted; the step keeps its connection_id and cannot run until it is pointed at another connection) or unavailable (the connection exists but the caller cannot see it, so it is not named). A step with no connection_id has neither field. Request bodies never accept these; they are stripped if echoed back. broken_step_count (steps whose state is missing) rides along, as on the list.