limits: raise message body cap 1k → 4k (catches ~95% of conversational overflow)

hive-c0re/src/agent_server.rs

@@ -178,7 +178,7 @@ async fn dispatch(req: &AgentRequest, agent: &str, coord: &Arc<Coordinator>) ->
 }
 
 /// Common Send handler shared between dispatch arms. Applies the
-/// 1 KiB body cap, then routes broadcast (`to == "*"`) vs unicast
+/// 4 KiB body cap, then routes broadcast (`to == "*"`) vs unicast
 /// through their respective broker calls. Pulled out of `dispatch`
 /// to keep that function under the clippy too-many-lines limit; the
 /// behaviour is identical to inlining.