Design §3.6 invariants #1/#2. A Sparkplug alias is scoped to ONE birth: after a
rebirth an edge node may point alias 5 at a different metric. So authored tags
bind by the stable metric NAME and the alias is a per-birth cache only —
RebuildFromBirth builds both indexes fresh and publishes them in one assignment,
never merging or upserting, including for an empty birth (which legitimately
clears the scope).
BirthCache keys scopes by the full (group, edgeNode, device?) triple and applies
the spec's node→device rules: an NBIRTH invalidates every DBIRTH under that node
(returning their metric sets for the STALE fan-out), a death evicts rather than
blanks so data-before-rebirth stays detectable. Reads are lock-free on MQTTnet's
dispatcher thread — an immutable snapshot swapped atomically per scope, the same
discipline MqttSubscriptionManager.AuthoredTable uses, with rebuilds landing in
place so a held table reference always observes the newest birth.
Running values are deliberately NOT stored here — LastValueCache owns those,
keyed by RawPath. SparkplugMetricBinding.Reinterpret exposes the birth datatype
to the codec's two's-complement fix, since a DATA metric carries no datatype.
Falsifiability: mutating RebuildFromBirth to merge reddened 5/19 tests (both
plan invariants); making the alias carry metric identity across a birth reddened
3/19, including the headline alias-reuse case.
Claude-Session: https://claude.ai/code/session_01GASWkNEi68FSCtvr6rLoEW
Joseph Doherty
2afef00eaa