fix: harden installer migration paths

bin/install.js

@@ -7199,9 +7199,35 @@ function resolveInstallRelativePath(baseDir, relPath) {
   if (fullPath !== root && !fullPath.startsWith(root + path.sep)) {
     return null;
   }
+  if (hasExistingSymlinkBetween(root, fullPath)) {
+    return null;
+  }
   return { relPath: normalized, fullPath };
 }
 
+function hasExistingSymlinkBetween(root, fullPath) {
+  const resolvedRoot = path.resolve(root);
+  const resolvedFullPath = path.resolve(fullPath);
+  if (resolvedFullPath !== resolvedRoot && !resolvedFullPath.startsWith(resolvedRoot + path.sep)) {
+    return true;
+  }
+
+  let cursor = resolvedRoot;
+  if (fs.existsSync(cursor) && fs.lstatSync(cursor).isSymbolicLink()) {
+    return true;
+  }
+
+  const relative = path.relative(resolvedRoot, resolvedFullPath);
+  for (const segment of relative.split(path.sep)) {
+    if (!segment) continue;
+    cursor = path.join(cursor, segment);
+    if (!fs.existsSync(cursor)) return false;
+    if (fs.lstatSync(cursor).isSymbolicLink()) return true;
+  }
+
+  return false;
+}
+
 /**
  * Write file manifest after installation for future modification detection
  */