fix(communication): resolve Communication-012..015 — endpoint-aware gRPC client cache, address-change recreation, correlation-id validation, node-flip tests

src/ScadaLink.Communication/Grpc/SiteStreamGrpcServer.cs

@@ -95,6 +95,18 @@ public class SiteStreamGrpcServer : SiteStreamService.SiteStreamServiceBase
         if (!_ready)
             throw new RpcException(new GrpcStatus(StatusCode.Unavailable, "Server not ready"));
 
+        // Communication-014: correlation_id arrives off the wire on a public gRPC
+        // endpoint and is used (below) to compose an Akka actor name. Akka actor names
+        // have a restricted character set — a id containing '/', whitespace, or other
+        // disallowed characters would make ActorOf throw InvalidActorNameException,
+        // escaping as an unhandled RPC fault. Reject unsafe ids cleanly up front.
+        if (string.IsNullOrEmpty(request.CorrelationId) ||
+            !ActorPath.IsValidPathElement(request.CorrelationId))
+        {
+            throw new RpcException(new GrpcStatus(
+                StatusCode.InvalidArgument, "correlation_id is missing or not a valid identifier"));
+        }
+
         // Duplicate prevention -- cancel existing stream for this correlationId
         if (_activeStreams.TryRemove(request.CorrelationId, out var existingEntry))
         {