fix(opcua,drivers): carry driver status sub-codes to clients (#519) + health-write ordering (#517)

#519 — a driver's OPC UA status code now reaches a client with its sub-code intact.
DriverInstanceActor projected the driver's uint onto a 3-state Good/Uncertain/Bad enum
and OtOpcUaNodeManager re-expanded Bad to a bare 0x80000000, so BadNoCommunication,
BadTypeMismatch and BadNotSupported were indistinguishable on the wire and every
driver's status constants (incl. the 16 #497 had just corrected) were diagnostic in
logs only. Resolved by option (b): the raw uint rides AttributeValuePublished ->
AttributeValueUpdate -> IOpcUaAddressSpaceSink.WriteValue, OpcUaQuality is deleted, and
severity classification is a helper (OpcUaStatus.IsGood/IsUncertain/IsBad).

The surface was wider than the issue costed (41 files, not "the sink and 3
implementations"): OpcUaQuality had non-driver producers with no uint to carry.
Each got its natural code — BadInternalError for a failed virtual-tag script,
BadNoCommunication for driver comms loss — and ScriptedAlarmHostActor's pair of
mutually-inverse uint<->enum mappers is deleted, having round-tripped a code the
engine already held. AddressSpaceApplier's removal writes deliberately keep the
generic Bad: not losing a code the driver had is this issue; inventing one for the
deploy path is a separate call.

Behaviour change: WriteAlarmQuality fires its Part 9 event on a status-code change
rather than a severity-bucket change. While the annotation was 3-state those were the
same predicate; now a move between two Bad reasons changes what a subscriber reads.

New SDK-free named constants live on Commons.OpcUa.OpcUaStatus, and
StatusCodeParityTests is widened to cover them — that guard is reflection-driven, so
it can only see a named constant, never an inline literal.

#517 — the symptom is real but the issue named the wrong path and its fix was unsafe.
ShutdownAsync cannot race: DriverInstanceActor calls it from PostStop, after the
mailbox drains. (Core/Hosting/DriverHost, the one class with a concurrent GetHealth,
has no production call site.) InitializeAsync can: it runs on a fire-and-forget
Task.Run, and MTConnectDriver writes Healthy then starts loops that can throw into a
catch which disposes the client before writing Faulted.

Moving the write earlier, as suggested, inverts the terminal state — teardown drains
in-flight loops that write health as they unwind, so a late loop could leave Healthy at
rest with every connection closed. The fix is a bracket (conservative before, terminal
after), applied to MTConnect's init-failure path only; shutdown keeps its single
trailing write, and the rule plus the reachability table are documented on
IDriver.ShutdownAsync.

CalculationDriver.GetHealth returned a hard-coded Healthy that consulted nothing —
Healthy before initialize, after shutdown and after dispose. Now derived from _running.
Its test, named Health_is_always_Connected, asserted the defect and is replaced.

Every new guard was falsified by breaking the production code and watching it go red.
The two sub-code tests each assert two different Bad codes, since a single-code
assertion could pass against a hard-coded constant under the old projection.

Pre-existing failures, verified unchanged on a stashed tree and not chased: 4 in
Driver.AbLegacy.IntegrationTests (slc500/micrologix/plc5 fixtures not up) and 3 in
Host.IntegrationTests.

Closes #517
Closes #519

Claude-Session: https://claude.ai/code/session_015p7wGqy3YpZNCpDzTpGMKo

src/Core/ZB.MOM.WW.OtOpcUa.Core.Abstractions/IDriver.cs

@@ -38,11 +38,30 @@ public interface IDriver
     Task ReinitializeAsync(string driverConfigJson, CancellationToken cancellationToken);
 
     /// <summary>Stop the driver, close connections, release resources. Called on shutdown or driver removal.</summary>
+    /// <remarks>
+    ///     <para><b>Land the terminal health value AFTER the teardown, never only before it</b> (Gitea #517).
+    ///     Teardown drains in-flight poll / probe loops, and those loops write health as they unwind — so a
+    ///     driver that wrote <see cref="DriverState.Unknown"/> first and then tore down could have a late
+    ///     loop overwrite it with <see cref="DriverState.Healthy"/> and leave THAT as the resting state,
+    ///     with every connection already closed. This is why the fleet writes last, and it is the reason
+    ///     #517's original suggestion — "write the transitional value before disposing" — is only safe as an
+    ///     ADDITIONAL write, bracketing the teardown, rather than as a move.</para>
+    ///     <para>Bracketing matters wherever a <see cref="GetHealth"/> can land mid-teardown. It cannot on
+    ///     this path today: <c>DriverInstanceActor</c> calls this from <c>PostStop</c>, on the actor thread,
+    ///     after the mailbox has drained, so its health poll is serialised against it. It CAN on the
+    ///     initialize path, which the same actor runs on a fire-and-forget <c>Task.Run</c> while the health
+    ///     tick keeps firing — so a driver whose <see cref="InitializeAsync"/> disposes anything on its
+    ///     failure path must write the failed state before disposing as well as after.</para>
+    /// </remarks>
     /// <param name="cancellationToken">Cancellation token for the operation.</param>
     /// <returns>A task that represents the asynchronous operation.</returns>
     Task ShutdownAsync(CancellationToken cancellationToken);
 
-    /// <summary>Current health snapshot, polled by Core for the status dashboard and ServiceLevel.</summary>
+    /// <summary>Current health snapshot, polled by Core for the status dashboard and ServiceLevel.
+    /// <para>Must reflect the driver's ACTUAL state rather than a constant — a hard-coded
+    /// <see cref="DriverState.Healthy"/> reports a healthy driver after shutdown and before initialize
+    /// alike, which is what Gitea #517 found in <c>CalculationDriver</c>. A driver with no transport still
+    /// has a running / not-running distinction worth reporting.</para></summary>
     /// <returns>The driver's current health snapshot.</returns>
     DriverHealth GetHealth();