Resolve all high-severity architecture review findings

src/ZB.MOM.WW.ScadaBridge.Communication/Grpc/CentralControlGrpcService.cs

@@ -56,8 +56,9 @@ namespace ZB.MOM.WW.ScadaBridge.Communication.Grpc;
 /// to the peer central node only when the call provably never ran. So:
 /// </para>
 /// <list type="bullet">
-///   <item><see cref="StatusCode.Unavailable"/> — this node is not ready; nothing was dispatched,
-///   so a cross-node retry is safe and correct.</item>
+///   <item><see cref="StatusCode.Unavailable"/> plus the server-owned not-started trailer — this
+///   node is not ready; nothing was dispatched, so a cross-node retry is safe. Unavailable alone
+///   can also be generated by a transport after application and does not prove retry safety.</item>
 ///   <item><see cref="StatusCode.DeadlineExceeded"/> — the <c>Ask</c> timed out. The message WAS
 ///   delivered and may have been processed; retrying it on the other node would duplicate work.</item>
 ///   <item><see cref="StatusCode.Internal"/> — the handler faulted (a piped
@@ -170,7 +171,7 @@ public sealed class CentralControlGrpcService : CentralControlService.CentralCon
         var central = RequireReady(context);
         var response = await AskAsync<NotificationStatusResponse>(
             central,
-            CentralControlDtoMapper.FromDto(request),
+            CentralControlDtoMapper.FromDto(request) with { VerifiedSourceSiteId = CentralControlSiteIdentity.RequireVerified(context) },
             _options.NotificationForwardTimeout,
             context).ConfigureAwait(false);
 
@@ -332,9 +333,7 @@ public sealed class CentralControlGrpcService : CentralControlService.CentralCon
             + "the peer central node).",
             context.Method);
 
-        throw new RpcException(new GrpcStatus(
-            StatusCode.Unavailable,
-            "Central control plane is not ready: the actor system is still starting."));
+        throw GrpcRetrySafety.NotDispatched("Central control plane is not ready: the actor system is still starting.");
     }
 
     /// <summary>