OtOpcUaTelemetry (Commons/Observability) centralizes the project's Meter
+ ActivitySource so all instrumentation points emit through a single
named surface. Counters cover the hot paths:
otopcua.deploy.applied (outcome=ack|reject)
otopcua.deploy.apply.duration (s, histogram)
otopcua.driver.lifecycle (event=spawn|spawn_stub|stop|fault)
otopcua.virtualtag.eval (outcome=ok|fail|skip)
otopcua.scriptedalarm.transition (state=activated|acknowledged|cleared)
otopcua.opcua.sink.write (kind=value|alarm|rebuild)
otopcua.redundancy.service_level_change (level=byte)
Plus two ActivitySource spans:
otopcua.deploy.apply wraps DriverHostActor.ApplyAndAck
otopcua.opcua.address_space_rebuild wraps OpcUaPublishActor.HandleRebuild
Instruments are no-op until a listener attaches, so tests + dev hosts
pay nothing for unread telemetry.
Host Program.cs gains AddOtOpcUaObservability() (binds the OtOpcUa Meter
+ ActivitySource to OpenTelemetry, attaches a Prometheus exporter) and
MapOtOpcUaMetrics() (mounts /metrics scrape endpoint). Driver-side
internals + ASP.NET request metrics deliberately stay off — the scrape
payload is scoped to OtOpcUa signals only.
Tests use MeterListener + ActivityListener to verify
VirtualTagActor.eval, OpcUaPublishActor.AttributeValueUpdate, and
RebuildAddressSpace actually emit on the central instruments. Runtime
suite is 72 / 72 green (+3).
Closes#105. Path A (F13b/c/d) complete; next batch options: #85 UNS
folder hierarchy in SDK, or F8b/F9b production engine bindings.
