fix(ui): replace bare crypto.randomUUID with uniqueId fallback and show WS disconnect error

- use-chat-sessions, skill-upload-dialog: replace crypto.randomUUID()
  with uniqueId() which has a UUID v4 fallback for non-secure contexts
  (HTTP without localhost) where crypto.randomUUID is unavailable
- use-chat-send: show localized error message when WebSocket is not
  connected instead of silently dropping the send
- Add error.notConnected i18n key to en/vi/zh chat locale files

Closes #352

ui/web/src/i18n/locales/en/chat.json

@@ -18,5 +18,8 @@
     "attached": "attached"
   },
   "forwardedFrom": "Forwarded from",
-  "replyingTo": "Replying to"
+  "replyingTo": "Replying to",
+  "error": {
+    "notConnected": "Not connected. Please wait for the connection to be established."
+  }
 }

ui/web/src/i18n/locales/vi/chat.json

@@ -18,5 +18,8 @@
   "newChat": "Trò chuyện mới",
   "openSessions": "Mở phiên",
   "readOnly": "Chỉ đọc — phiên này thuộc về người dùng khác",
-  "replyingTo": "Đang trả lời"
+  "replyingTo": "Đang trả lời",
+  "error": {
+    "notConnected": "Chưa kết nối. Vui lòng chờ kết nối được thiết lập."
+  }
 }

ui/web/src/i18n/locales/zh/chat.json

@@ -18,5 +18,8 @@
   "newChat": "新建对话",
   "openSessions": "打开Session",
   "readOnly": "只读 — 此Session属于其他用户",
-  "replyingTo": "回复"
+  "replyingTo": "回复",
+  "error": {
+    "notConnected": "未连接。请等待连接建立。"
+  }
 }

ui/web/src/pages/chat/hooks/use-chat-send.ts

@@ -1,4 +1,5 @@
 import { useState, useCallback } from "react";
+import { useTranslation } from "react-i18next";
 import { useWs, useHttp } from "@/hooks/use-ws";
 import { Methods } from "@/api/protocol";
 import type { ChatMessage } from "@/types/chat";
@@ -25,6 +26,7 @@ export function useChatSend({
   onMessageAdded,
   onExpectRun,
 }: UseChatSendOptions) {
+  const { t } = useTranslation("chat");
   const ws = useWs();
   const http = useHttp();
   const [sending, setSending] = useState(false);
@@ -34,7 +36,11 @@ export function useChatSend({
     async (message: string, sessionKey: string, files?: AttachedFile[]) => {
       const hasMessage = message.trim().length > 0;
       const hasFiles = files && files.length > 0;
-      if (!ws.isConnected || (!hasMessage && !hasFiles) || !sessionKey) return;
+      if (!ws.isConnected) {
+        setError(t("error.notConnected"));
+        return;
+      }
+      if ((!hasMessage && !hasFiles) || !sessionKey) return;
 
       const trimmed = message.trim();
       setError(null);

ui/web/src/pages/chat/hooks/use-chat-sessions.ts

@@ -7,6 +7,7 @@ import { useAuthStore } from "@/stores/use-auth-store";
 import { toast } from "@/stores/use-toast-store";
 import i18next from "i18next";
 import { userFriendlyError } from "@/lib/error-utils";
+import { uniqueId } from "@/lib/utils";
 
 /**
  * Manages the session list for the chat sidebar.
@@ -45,7 +46,7 @@ export function useChatSessions(agentId: string) {
   }, [loadSessions]);
 
   const buildNewSessionKey = useCallback(() => {
-    const convId = crypto.randomUUID();
+    const convId = uniqueId();
     return `agent:${agentId}:ws:direct:${convId}`;
   }, [agentId]);
 

ui/web/src/pages/skills/skill-upload-dialog.tsx

@@ -11,6 +11,7 @@ import {
 } from "@/components/ui/dialog";
 import { Button } from "@/components/ui/button";
 import { validateSkillZip } from "./lib/validate-skill-zip";
+import { uniqueId } from "@/lib/utils";
 
 type FileStatus = "validating" | "valid" | "invalid" | "uploading" | "success" | "error";
 
@@ -46,7 +47,7 @@ export function SkillUploadDialog({ open, onOpenChange, onUpload }: SkillUploadD
     if (fresh.length === 0) return;
 
     const pending: FileEntry[] = fresh.map((f) => ({
-      id: crypto.randomUUID(),
+      id: uniqueId(),
       file: f,
       status: "validating" as const,
     }));