Fix same-window folder drop guard

server/public/app.js

@@ -892,11 +892,18 @@ async function finishItemPointerDrag(event, move, up) {
   }
 
   try {
-    const destination = `${target.path.replace(/\/$/, '')}/${drag.name}`;
-    if (destination === drag.path) {
+    const destination = joinPath(target.path, drag.name);
+    recordDebug('pointer.destination', {
+      source: drag.path,
+      targetPath: target.path,
+      destination,
+      targetIsRow: Boolean(target.row),
+      copy: event.altKey
+    });
+    if (destination === drag.path || target.path === drag.path) {
       throw new Error('Quelle und Ziel sind identisch.');
     }
-    if (drag.type === 'directory' && target.path.startsWith(`${drag.path.replace(/\/$/, '')}/`)) {
+    if (drag.type === 'directory' && isPathInside(target.path, drag.path)) {
       throw new Error('Ein Ordner kann nicht in sich selbst verschoben werden.');
     }
     await createJob(event.altKey ? 'copy' : 'move', drag.path, destination, [drag.sourceWindowId, target.windowId]);
@@ -1132,6 +1139,21 @@ function dirname(value) {
   return `/${parts.slice(0, -1).join('/')}`;
 }
 
+function joinPath(parent, name) {
+  return `${String(parent || '').replace(/\/+$/, '')}/${String(name || '').replace(/^\/+/, '')}`;
+}
+
+function normalizePath(value) {
+  const parts = String(value || '').split('/').filter(Boolean);
+  return `/${parts.join('/')}`;
+}
+
+function isPathInside(path, parent) {
+  const normalizedPath = normalizePath(path);
+  const normalizedParent = normalizePath(parent);
+  return normalizedPath.startsWith(`${normalizedParent.replace(/\/$/, '')}/`);
+}
+
 function formatBytes(bytes) {
   const value = Number(bytes || 0);
   if (value < 1024) return `${value} B`;