Keep subtag acks and alarm reads safe on the managed ack path

Review fixes for the opt-in managed GUID ack:

- Subtag-mode GUID acks (forced subtag, or failover on the standby) stay on
  the consumer; their GUIDs are synthetic and only the subtag consumer can
  resolve them. Forced-subtag sessions no longer build a managed client.
- A failed managed Initialize/Register/Subscribe drops back to the wnwrap
  ack path instead of failing the alarm subscription.
- Drop stale crefs to a nonexistent Unverified member in
  WnalNativeAckConsumer.
- Unit tests for routing, fallback, and disposal; document
  MXGATEWAY_USE_MANAGED_ALARM_ACK.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

docs/AlarmClientDiscovery.md

@@ -793,6 +793,28 @@ in the codebase for the forward-compat shape, but the gateway-side
 `AcknowledgeAlarmByName` when the public RPC supplies a recognizable
 `Provider!Group.Tag` reference.
 
+**Opt-in managed GUID ack.** Setting `MXGATEWAY_USE_MANAGED_ALARM_ACK=1`
+in the gateway's environment (workers inherit it) routes GUID-keyed acks
+through `aaAlarmManagedClient.AlarmClient.AlarmAckByGUID` instead of the
+wnwrap method. That managed method is implemented on this build and
+carries operator domain and full name natively. The worker reaches it by
+reflection (`AaManagedAlarmAckConsumer`) because the members are
+non-public, and runs its own Initialize → Register → Subscribe lifecycle
+against the alarm subscription expression. The path is deliberately
+conservative:
+
+- If the DLL cannot load or the lifecycle returns a non-zero status, the
+  worker drops back to the wnwrap ack path; alarm reads never fail
+  because of it.
+- Subtag-mode acks (forced subtag, or failover currently on the standby)
+  stay on the subtag consumer: their GUIDs are synthetic and only it can
+  resolve them.
+- By-name acks stay on wnwrap — `AlarmClient` has no by-name ack.
+
+A zero return still means *accepted*, not *applied*; a secured
+(`MxSecurityOperate`) alarm needs an authenticated operator. The skip-gated
+`AlarmManagedGuidAckLiveSmokeTests` asserts the ack actually lands.
+
 ### 5. STA / threading — resolved
 
 The wnwrap COM is `ThreadingModel=Apartment`. The consumer's