Add validation for customOutDir to prevent file path from being used as directory

Co-authored-by: mifi <402547+mifi@users.noreply.github.com>

src/renderer/src/hooks/useUserSettingsRoot.ts

@@ -10,6 +10,7 @@ import { mySpring, emitter as animationsEmitter } from '../animations';
 
 const { configStore } = window.require('@electron/remote').require('./index.js');
 const { systemPreferences } = window.require('@electron/remote');
+const { lstat } = window.require('fs/promises');
 
 const animationSettings = systemPreferences.getAnimationSettings();
 
@@ -56,6 +57,31 @@ export default function useUserSettingsRoot() {
   useEffect(() => safeSetConfig({ captureFormat }), [captureFormat]);
   const [customOutDir, setCustomOutDir] = useState(safeGetConfigInitial('customOutDir'));
   useEffect(() => safeSetConfig({ customOutDir }), [customOutDir]);
+
+  // Validate customOutDir on mount - reset if it's not a valid directory
+  // This prevents issues where customOutDir was set to a file path instead of a directory
+  // https://github.com/mifi/lossless-cut/issues/XXXX
+  useEffect(() => {
+    async function validateCustomOutDir() {
+      if (customOutDir == null) return;
+
+      try {
+        const stat = await lstat(customOutDir);
+        if (!stat.isDirectory()) {
+          console.warn('customOutDir is not a directory, resetting:', customOutDir);
+          setCustomOutDir(undefined);
+        }
+      } catch (err) {
+        // If we can't stat the path (doesn't exist, permission denied, etc.), reset it
+        console.warn('customOutDir is invalid, resetting:', customOutDir, err);
+        setCustomOutDir(undefined);
+      }
+    }
+
+    validateCustomOutDir();
+    // eslint-disable-next-line react-hooks/exhaustive-deps
+  }, []); // Only run on mount
+
   const [keyframeCut, setKeyframeCut] = useState(safeGetConfigInitial('keyframeCut'));
   useEffect(() => safeSetConfig({ keyframeCut }), [keyframeCut]);
   const [preserveMetadata, setPreserveMetadata] = useState(safeGetConfigInitial('preserveMetadata'));