}
        }
        return out;
    }

    private static List<String> parentCommitsOf(String commit) throws IOException, InterruptedException, ExecutionException {
        String stdout = getStdout(new String[] {"git", "show", "--format=%P", "--no-patch", "--no-show-signature", commit});
        String trimmed = stdout.trim();
        if (trimmed.isEmpty()) {
            return Collections.emptyList();
        }