Transport: assert sender is faulty when mutating message

Author: joaomlneto

simulator/src/main/java/byzzbench/simulator/transport/Transport.java

@@ -334,6 +334,13 @@ public synchronized void applyMutation(long eventId, Fault fault) {
                     "Event %d is not a message - cannot mutate it.", eventId));
         }
 
+        // check if sender is faulty
+        if (!this.scenario.isFaultyReplica(m.getSenderId())) {
+            throw new IllegalArgumentException(
+                    String.format("Cannot mutate message: sender %s is not marked as faulty", m.getSenderId())
+            );
+        }
+
         // create input for the fault
         FaultContext input = new FaultContext(this.scenario, e);