BUG #19488: Standby connection fails after dropping on login event trigger enabled always

The following bug has been logged on the website:

Bug reference: 19488
Logged by: Egor Chindyaskin
Email address: kyzevan23(at)mail(dot)ru
PostgreSQL version: 18.4
Operating system: Ubuntu 26.04
Description:

Hello!
In a master + physical standby setup, connection to the standby fails after
creating a login event trigger on the master, enabling it as always, and
then dropping it without reconnecting to the master.
Also reproduces on master branch.
Steps to reproduce:

1. Run the following SQL script on the master:
CREATE OR REPLACE FUNCTION init_session()
RETURNS event_trigger SECURITY DEFINER
LANGUAGE plpgsql AS
$$
BEGIN
RAISE NOTICE 'init_session';
END;
$$;

CREATE EVENT TRIGGER init_session
ON login
EXECUTE FUNCTION init_session();

ALTER EVENT TRIGGER init_session ENABLE ALWAYS;

DROP EVENT TRIGGER init_session;

2. Try to connect to the standby:
psql -p5433

Result:
psql: error: connection to server on socket "/tmp/.s.PGSQL.5433" failed:
FATAL: cannot acquire lock mode AccessExclusiveLock on database objects
while recovery is in progress
HINT: Only RowExclusiveLock or less can be acquired on database objects
during recovery.

--
With best regards,
Egor Chindyaskin

Postgres Professional: https://postgrespro.com