The MxGateway alarm mapper emits the SnapshotComplete framing sentinel with
empty SourceReference/SourceObjectReference. HandleAlarmTransitionReceived
routed every transition by prefix match against the subscriber's source, so
the empty-ref sentinel ('' .StartsWith("<src>.") == false) was dropped for
any specific source. The NativeAlarmActor buffers snapshot conditions and only
flushes them on SnapshotComplete, so statically-active native alarms delivered
only in the initial snapshot (no later live transition) never surfaced.
Broadcast the SnapshotComplete sentinel to all alarm subscribers (bypassing the
source match + type filter) so each NativeAlarmActor's snapshot swap completes.
Adds a regression test using the real empty-ref sentinel against a specific
(prefix) source.
Joseph Doherty