fixing idempotency_enforced in a2a.proto

Author: maeste

specification/grpc/a2a.proto

@@ -418,8 +418,8 @@ message AgentCapabilities {
   bool push_notifications = 2;
   // Extensions supported by this agent.
   repeated AgentExtension extensions = 3;
-  // If the agent supports messageId-based idempotency for task creation
-  bool idempotency_supported = 4;
+  // If the agent supports messageId-based idempotency for message send
+  bool idempotency_enforced = 4;
 }
 
 // A declaration of an extension supported by an Agent.