fix(P4A): guard ImageAnnotator load callbacks with cancelled flag (React strict double-mount)

apps/desktop/src/components/ImageAnnotator.tsx

@@ -51,18 +51,31 @@ export function ImageAnnotator({ file, onCancel, onSave }: Props) {
   useEffect(() => { onCancelRef.current = onCancel; }, [onCancel]);
 
   useEffect(() => {
+    // React 18 strict mode in dev double-mounts effects to test idempotency.
+    // The first run creates a blob URL, sets img.src, returns a cleanup
+    // that revokes — and the cleanup fires BEFORE the (still-in-flight)
+    // image fetch completes. The browser then emits ERR_FILE_NOT_FOUND for
+    // the revoked URL → img.onerror → modal closes instantly. The
+    // `cancelled` flag guards every callback so a torn-down run can't
+    // close the modal that the second mount just opened.
+    let cancelled = false;
     const url = URL.createObjectURL(file);
     const img = new Image();
     img.onload = () => {
+      if (cancelled) return;
       imageRef.current = img;
       setImageLoaded(true);
     };
     img.onerror = () => {
+      if (cancelled) return;
       console.error('ImageAnnotator: failed to decode source image');
       onCancelRef.current();
     };
     img.src = url;
-    return () => URL.revokeObjectURL(url);
+    return () => {
+      cancelled = true;
+      URL.revokeObjectURL(url);
+    };
   }, [file]);
 
   useEffect(() => {