Review (fa45b0e6): paho's connect() does not wait for the CONNACK, so C0
could read protocol_levels before the broker had handled the second
CONNECT, and the `before` slice could take in a previous test's connection.
- _Client waits for CONNACK (and UNSUBACK, instead of sleeping 0.3 s);
C0 checks the levels of its own two client ids (stats() levels_by_client).
- The local broker now routes and stores a PUBLISH before its PUBACK, so a
publisher holding the ack may rely on the retained state it asked for
(late subscriber replay, retained delete).
- test_c0_holds_when_the_broker_is_slow runs C0 with CONNECT/UNSUBSCRIBE
delayed and PUBLISH routed late; the old C0 fails it ([] == [4, 4]), as do
an ack-before-route broker and a fixed-sleep unsubscribe.
Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
GodopuandClaude Opus 5.5
b58edace11