Make prompt debug creation concurrency safe

internal/promptdebug/debug_writer.go

@@ -269,7 +269,23 @@ func ensureSecureDirectory(path string) error {
 		info, err := os.Lstat(current)
 		if os.IsNotExist(err) {
 			if err := os.Mkdir(current, debugDirectoryMode); err != nil {
-				return err
+				if !os.IsExist(err) {
+					return err
+				}
+				info, err = os.Lstat(current)
+				if err != nil {
+					return err
+				}
+				if info.Mode()&os.ModeSymlink != 0 {
+					return fmt.Errorf("directory component %q must not be a symlink", current)
+				}
+				if !info.IsDir() {
+					return fmt.Errorf("directory component %q is not a directory", current)
+				}
+				if err := os.Chmod(current, debugDirectoryMode); err != nil {
+					return err
+				}
+				continue
 			}
 			if err := os.Chmod(current, debugDirectoryMode); err != nil {
 				return err