Replaces the Ok=true stub with a TCP connect to the peer's OPC UA port (4840
default) with a 2s timeout. A successful connect indicates the OPC UA server
process is up + accepting connections — enough for the redundancy calculator
to treat the peer as live. A full secure-channel Hello/Acknowledge handshake
is overkill for what the redundancy calc consumes and would pull in the OPC
UA Client SDK + a PKI setup. Upgrade later if a deeper liveness signal is ever
required.
Probe extracts the host from NodeId by stripping the :port suffix (commit
5cfbe8b encoded host:port into NodeId for cluster-member identity).
Tests: 2 new tests — Ok=true against a live TcpListener on a chosen port,
Ok=false against an unreachable endpoint. All 17 Runtime tests pass (was 16
covering only the message-contract surface).
Mirrors WithOtOpcUaControlPlaneSingletons for the driver role. Spawns
DriverHostActor + DbHealthProbeActor on the host's ActorSystem and
registers both under marker keys. Host's Program.cs now calls it when
the node carries the driver role, so driver-only and admin+driver
deployments both auto-bootstrap the per-node actors.
Integration test covers the registration round-trip via Microsoft.Extensions.Hosting
+ Akka.Hosting AddAkka.
