SparkplugRebirthScope (the AdminUI's typed input) rejects '+'/'#' and its own
remarks say it is 'advisory, not the gate' because MqttBrowseSession
.ResolveRebirthTargets 'refuses an unusable one BEFORE any message leaves'. That
claim was false: the bare {group}/{edgeNode} branch — honoured on purpose, since a
node that has not birthed is the prime rebirth target — gated on IsUsableLabel,
which checks length and control characters only. A scope of 'Plant1/#' therefore
published spBv1.0/Plant1/NCMD/# , a PUBLISH the MQTT spec forbids and a conformant
broker answers by closing the browse connection; '+' would have fanned one
operator click across every matching edge node.
The check is a separate IsUsableRebirthSegment rather than a tightening of
IsUsableLabel: that helper also judges Sparkplug METRIC names, which are arbitrary
publisher-chosen UTF-8 and never part of a topic, so tightening it there would drop
legitimate metrics from the tree. Cases 1 and 2 cannot reach this shape — their ids
come off SparkplugTopic.TryParse, which already rejects both characters.
Driver.Mqtt.Tests 724 (was 708).
Joseph Doherty
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