fix(rest-api): complete review hardening

Co-authored-by: jidechao <62241490+jidechao@users.noreply.github.com>

Author: KylinMountain

frontend/src/hooks/useSSEStream.js

@@ -57,8 +57,12 @@ export function useSSEStream() {
         onEvent("error", { message: err?.message || t("requestFailed") });
       }
     } finally {
-      ctrlRef.current = null;
-      setBusy(false);
+      // A replaced stream may finish after its successor has started. Only
+      // clear state when this controller still owns the active stream.
+      if (ctrlRef.current === ctrl) {
+        ctrlRef.current = null;
+        setBusy(false);
+      }
     }
   }, [t]);
 

frontend/src/views/Chat.jsx

@@ -36,11 +36,13 @@ export default function Chat({ kb }) {
   useEffect(() => { if (scrollRef.current) scrollRef.current.scrollTop = scrollRef.current.scrollHeight; }, [msgs]);
 
   function newSession() {
+    stop();
     setSessionId(null);
     setMsgs([]);
   }
 
   async function loadHistory(sid) {
+    stop();
     setSessionId(sid);
     setMsgs([]);
     try {

openkb/agent/chat.py

@@ -30,6 +30,7 @@
     build_query_agent,
     iter_agent_response_events,
 )
+from openkb.config import LlmCredentialBundle
 from openkb.log import append_log
 
 _STYLE_DICT: dict[str, str] = {