fix(runtime): evict a stopped driver's retained values from the dependency mux

DriverHostActor now tells the mux SourceRemoved(driverInstanceId)
wherever a driver object ends: StopChild (deploy removal and the stop
half of a config-change respawn) and an operator Restart. It is not
sent on a supervision restart, which re-uses the same driver. Before
this nothing sent it, so a removed driver's last Good stayed in the
mux and replayed to the next replay-opting subscriber as current.

DriverHostActorSourceRemovedTests drives a real mux with two real
driver children: after a deploy drops DI-1 only DI-2's value replays
(positive control: both replay before the removal), and a supervision
restart of DI-1 leaves its value replayable.

Residual (documented on EvictRetainedValues): a burst the old child
enqueued just before it stopped can still be forwarded after the
eviction; the next publish, a comms-loss fan or the grace sweep
bounds it.

Refs #731 #734
Claude-Session: https://claude.ai/code/session_01Ub9hGmYLQvn9XETzw7CMsT

src/Server/ZB.MOM.WW.OtOpcUa.Runtime/Drivers/DriverHostActor.cs

@@ -3840,6 +3840,7 @@ public sealed class DriverHostActor : ReceiveActor, IWithTimers, IWithUnboundedS
         StopDependencyAdapter(driverInstanceId);
         Context.Stop(entry.Actor);
         _children.Remove(driverInstanceId);
+        EvictRetainedValues(driverInstanceId);
         // The instance left the plan (StopChild is only reached via plan.ToStop), so its cached
         // Health/Resilience snapshots must not replay to new telemetry subscribers. Release the shared
         // resilience state FIRST: the resilience publisher re-emits the tracker's snapshots every tick, so
@@ -3858,6 +3859,25 @@ public sealed class DriverHostActor : ReceiveActor, IWithTimers, IWithUnboundedS
         _log.Info("DriverHost {Node}: stopped driver child {Id}", _localNode, driverInstanceId);
     }
 
+    /// <summary>
+    ///     Tells the dependency mux to drop every retained value this driver instance produced, so a stopped
+    ///     driver's last Good is never replayed to a later replay-opting subscriber as if it were current. Sent
+    ///     wherever a driver OBJECT ends: a deploy removal, the stop half of a config-change respawn
+    ///     (<see cref="StopChild"/>) and an operator Restart (a new driver object). Deliberately NOT sent on a
+    ///     supervision restart (<see cref="HandleReprovisionRequested"/>): that re-uses the same driver, whose last value is
+    ///     still its current one. Sent before any respawn, on the same host→mux pair the new incarnation's
+    ///     values travel, so the eviction is ordered ahead of them.
+    /// </summary>
+    /// <remarks>
+    ///     Residual: a burst the old child enqueued on this host just before it stopped can still be forwarded
+    ///     after the eviction and re-retain a value. The window is one mailbox drain; a comms-loss fan or the
+    ///     next real publish overwrites it, and the mux's grace sweep bounds it once no replay subscriber holds
+    ///     the ref.
+    /// </remarks>
+    /// <param name="driverInstanceId">The driver instance that ended.</param>
+    private void EvictRetainedValues(string driverInstanceId) =>
+        _dependencyMux?.Tell(new DependencyMuxActor.SourceRemoved(driverInstanceId));
+
     private static string ActorNameFor(string driverInstanceId, long generation)
     {
         // Akka actor names cannot contain '/', ':', or whitespace. Mangle defensively. The monotonic
@@ -3905,6 +3925,9 @@ public sealed class DriverHostActor : ReceiveActor, IWithTimers, IWithUnboundedS
         StopDependencyAdapter(msg.DriverInstanceId);
         Context.Stop(entry.Actor);
         _children.Remove(msg.DriverInstanceId);
+        // An operator Restart builds a NEW driver object, so the old one's retained values are evicted like a
+        // removal's; the respawned driver republishes its own.
+        EvictRetainedValues(msg.DriverInstanceId);
         // The old incarnation's health must not read as the new one's until it publishes its own.
         _healthPublisher.Forget(msg.DriverInstanceId);