fix: prevent page crash when deleting an agent (#514)

src/components/ui/confirm-dialog.tsx

@@ -2,7 +2,7 @@
  * ConfirmDialog - In-DOM confirmation dialog (replaces window.confirm)
  * Keeps focus within the renderer to avoid Windows focus loss after native dialogs.
  */
-import { useEffect, useRef } from 'react';
+import { useEffect, useRef, useState } from 'react';
 import { cn } from '@/lib/utils';
 import { Button } from '@/components/ui/button';
 
@@ -13,8 +13,9 @@ interface ConfirmDialogProps {
   confirmLabel?: string;
   cancelLabel?: string;
   variant?: 'default' | 'destructive';
-  onConfirm: () => void;
+  onConfirm: () => void | Promise<void>;
   onCancel: () => void;
+  onError?: (error: unknown) => void;
 }
 
 export function ConfirmDialog({
@@ -26,8 +27,19 @@ export function ConfirmDialog({
   variant = 'default',
   onConfirm,
   onCancel,
+  onError,
 }: ConfirmDialogProps) {
   const cancelRef = useRef<HTMLButtonElement>(null);
+  const [confirming, setConfirming] = useState(false);
+  const [prevOpen, setPrevOpen] = useState(open);
+
+  // Reset confirming when dialog closes (during render to avoid setState-in-effect)
+  if (prevOpen !== open) {
+    setPrevOpen(open);
+    if (!open) {
+      setConfirming(false);
+    }
+  }
 
   useEffect(() => {
     if (open && cancelRef.current) {
@@ -38,12 +50,27 @@ export function ConfirmDialog({
   if (!open) return null;
 
   const handleKeyDown = (e: React.KeyboardEvent) => {
-    if (e.key === 'Escape') {
+    if (e.key === 'Escape' && !confirming) {
       e.preventDefault();
       onCancel();
     }
   };
 
+  const handleConfirm = () => {
+    if (confirming) return;
+    const result = onConfirm();
+    if (result instanceof Promise) {
+      setConfirming(true);
+      result.catch((error) => {
+        if (onError) {
+          onError(error);
+        }
+      }).finally(() => {
+        setConfirming(false);
+      });
+    }
+  };
+
   return (
     <div
       className="fixed inset-0 z-50 flex items-center justify-center bg-black/50"
@@ -68,12 +95,14 @@ export function ConfirmDialog({
             ref={cancelRef}
             variant="outline"
             onClick={onCancel}
+            disabled={confirming}
           >
             {cancelLabel}
           </Button>
           <Button
             variant={variant === 'destructive' ? 'destructive' : 'default'}
-            onClick={onConfirm}
+            onClick={handleConfirm}
+            disabled={confirming}
           >
             {confirmLabel}
           </Button>