diff --git a/local-tool/frontend/src/components/devices/flash-dialog.tsx b/local-tool/frontend/src/components/devices/flash-dialog.tsx
index 0a57a12..39e6834 100644
--- a/local-tool/frontend/src/components/devices/flash-dialog.tsx
+++ b/local-tool/frontend/src/components/devices/flash-dialog.tsx
@@ -39,6 +39,7 @@ export function FlashDialog({ deviceId }: FlashDialogProps) {
   const device = devices.find((d) => d.id === deviceId);
   const selectedModel = models.find((m) => m.id === selectedModelId);
 
+  // S2: 資料載入前預設 compatible=true，避免在 model/device 還沒載入時就顯示不相容警告
   const compatible = useMemo(() => {
     if (!selectedModel || !device) return true;
     return isModelCompatible(selectedModel.supportedHardware, device.type);
@@ -56,30 +57,38 @@ export function FlashDialog({ deviceId }: FlashDialogProps) {
 
   const handleFlash = async () => {
     if (!selectedModelId) return;
-    // 1. Create WebSocket and wait for it to open
-    await connectAndWait();
-    // 2. Then start flash (POST) — now WS is listening
+    try {
+      await connectAndWait();
+    } catch (e) {
+      const msg = e instanceof Error ? e.message : String(e);
+      reset();
+      useFlashStore.getState().setError(msg);
+      return;
+    }
     await startFlash(deviceId, selectedModelId);
   };
 
+  // m2 fix: 進度尚未完成時（不管 isFlashing 狀態如何）都阻止關閉
+  const isInProgress = (isFlashing || (progress !== null && progress.percent < 100)) && !error;
+
   return (
     <Dialog open={open} onOpenChange={(v) => {
-      if (!v && isFlashing && !error) return;
+      if (!v && isInProgress) return;
       setOpen(v);
     }}>
       <DialogTrigger asChild>
-        <Button data-tour-id="flash-model-btn">Flash Model</Button>
+        <Button data-tour-id="flash-model-btn">載入模型</Button>
       </DialogTrigger>
       <DialogContent>
         <DialogHeader>
-          <DialogTitle>Flash Model to Device</DialogTitle>
+          <DialogTitle>載入模型到裝置</DialogTitle>
         </DialogHeader>
         <div className="space-y-4">
           {!isFlashing && !progress && !error ? (
             <>
               <Select value={selectedModelId} onValueChange={setSelectedModelId}>
                 <SelectTrigger>
-                  <SelectValue placeholder="Select a model" />
+                  <SelectValue placeholder="選擇模型" />
                 </SelectTrigger>
                 <SelectContent>
                   {models.map((m) => (
@@ -95,9 +104,9 @@ export function FlashDialog({ deviceId }: FlashDialogProps) {
                   <div className="flex gap-2 items-start">
                     <TriangleAlertIcon className="h-5 w-5 text-yellow-600 mt-0.5 shrink-0" />
                     <div className="text-sm">
-                      <p className="font-medium text-yellow-800">Hardware Incompatible</p>
+                      <p className="font-medium text-yellow-800">硬體不相容</p>
                       <p className="text-yellow-700">
-                        This model may not be compatible with {device ? getHardwareType(device.type) : 'this device'}.
+                        此模型可能與 {device ? getHardwareType(device.type) : '此裝置'} 不相容。
                       </p>
                     </div>
                   </div>
@@ -110,10 +119,10 @@ export function FlashDialog({ deviceId }: FlashDialogProps) {
                 className="w-full"
               >
                 {!selectedModelId
-                  ? 'Select a model'
+                  ? '請先選擇模型'
                   : !compatible
-                    ? 'Incompatible — Cannot Flash'
-                    : 'Start Flash'}
+                    ? '不相容 — 無法載入'
+                    : '開始載入'}
               </Button>
             </>
           ) : (
@@ -130,7 +139,7 @@ export function FlashDialog({ deviceId }: FlashDialogProps) {
                 setOpen(false);
               }}
             >
-              {error ? 'Close' : 'Done'}
+              {error ? '關閉' : '完成'}
             </Button>
           )}
         </div>
diff --git a/local-tool/frontend/src/components/devices/flash-progress.tsx b/local-tool/frontend/src/components/devices/flash-progress.tsx
index 796002f..597c8fb 100644
--- a/local-tool/frontend/src/components/devices/flash-progress.tsx
+++ b/local-tool/frontend/src/components/devices/flash-progress.tsx
@@ -19,14 +19,14 @@ export function FlashProgress({ progress, error, onRetry }: FlashProgressProps)
           <div className="flex gap-2 items-start">
             <XCircle className="h-5 w-5 text-red-600 mt-0.5 shrink-0" />
             <div className="flex-1">
-              <p className="font-medium text-red-800">Flash Failed</p>
+              <p className="font-medium text-red-800">模型載入失敗</p>
               <p className="text-sm text-red-700 mt-1">{error}</p>
             </div>
           </div>
         </div>
         {onRetry && (
           <Button onClick={onRetry} className="w-full" variant="outline">
-            Retry
+            重試
           </Button>
         )}
       </div>
@@ -37,7 +37,7 @@ export function FlashProgress({ progress, error, onRetry }: FlashProgressProps)
     return (
       <div className="space-y-2 text-center">
         <div className="animate-pulse text-sm text-muted-foreground">
-          Preparing flash...
+          正在準備載入...
         </div>
         <Progress value={0} />
       </div>
@@ -53,7 +53,7 @@ export function FlashProgress({ progress, error, onRetry }: FlashProgressProps)
       <Progress value={progress.percent} />
       <p className="text-sm text-muted-foreground">{progress.message}</p>
       {progress.percent >= 100 && (
-        <p className="text-sm font-medium text-green-600">Flash Complete!</p>
+        <p className="text-sm font-medium text-green-600">模型載入完成！</p>
       )}
     </div>
   );
diff --git a/local-tool/frontend/src/hooks/use-flash-progress.ts b/local-tool/frontend/src/hooks/use-flash-progress.ts
index f6da4d7..8bcaca4 100644
--- a/local-tool/frontend/src/hooks/use-flash-progress.ts
+++ b/local-tool/frontend/src/hooks/use-flash-progress.ts
@@ -29,16 +29,15 @@ export function useFlashProgress(deviceId: string) {
    */
   const connectAndWait = useCallback(
     () =>
-      new Promise<void>((resolve) => {
-        // Close any existing connection
+      new Promise<void>((resolve, reject) => {
         wsRef.current?.close();
 
-        let resolved = false;
+        let settled = false;
         const doResolve = () => {
-          if (!resolved) {
-            resolved = true;
-            resolve();
-          }
+          if (!settled) { settled = true; resolve(); }
+        };
+        const doReject = (reason: string) => {
+          if (!settled) { settled = true; reject(new Error(reason)); }
         };
 
         const ws = createWebSocket(
@@ -52,8 +51,8 @@ export function useFlashProgress(deviceId: string) {
         );
         wsRef.current = ws;
 
-        // Safety timeout — don't block forever
-        setTimeout(doResolve, 3000);
+        // m4 fix: timeout 時 reject 而非 resolve，讓 UI 顯示錯誤而非靜默繼續
+        setTimeout(() => doReject('WebSocket 連線逾時（3 秒），請確認伺服器是否正常運作'), 3000);
       }),
     [deviceId, updateProgress],
   );