close

Establishes an orderly shutdown boundary: rejects new work, bounds manager-job cancellation, admitted manager-operation draining, and admitted-writer draining, waits for the last serialized switch/association to finalize, then closes every manager-owned Room instance. If a cancelled child, admitted operation, writer, or pool close cannot finish successfully, ownership is retained and physical cleanup is skipped so a later close call can retry without losing track of live resources. Retried attempts may call Room's idempotent close() again for pools that completed during an earlier partial attempt.