Add an explicit _closing guard to both owned executors so the
recreate-on-shutdown path only recovers from an *external* teardown of
the loop default — never resurrects a pool the gateway/adapter itself
stopped. _shutdown_*executor() sets the flag; _get_*executor() raises if
closing; feishu connect() re-arms on reconnect. Updates the gateway
recreate test to assert the refusal contract and adds feishu coverage.
7ee0b68973