MqttMessageRouter matched purely on topic with no endpoint predicate, and
RouteAsync was not even passed an endpoint id. Topic filters routinely overlap
between brokers — every Tasmota install publishes tele/+/SENSOR — so with two
brokers a message on A was ingested by a source bound to B. HA enforced the
binding on both workers; MQTT enforced it only at subscribe time.
Pass the endpoint id through: MQTTnet's event args carry the topic but not the
delivering connection, so CreateClient captures the id in the handler closure.
ResolveTopicsAsync drops its `|| EndpointId == null` clause to match, since an
unbound source is no longer routed and subscribing its topic everywhere would
only invite traffic nothing consumes.
That last part would silently kill unbound sources that work today, so a data
migration binds them to the single broker when exactly one exists — the case
where old and new behaviour coincide. Two or more brokers is left alone: the
old behaviour was already ambiguous and a guess could route a meter's data to
the wrong broker. HA sources are excluded; they have always required an
endpoint, so binding them would activate ingestion never previously running.
Claude-Session: https://claude.ai/code/session_01V6joyergfvVLFEizH1hJLd
