// Initial version should be 0
        assertEquals(0, keyManager.getKeyVersion(sessionId), "Initial version should be 0");

        // Rotate key
        int newVersion = keyManager.rotateSessionKey(sessionId);
        assertEquals(1, newVersion, "New version should be 1");
        assertEquals(1, keyManager.getKeyVersion(sessionId), "Key version should be updated");

        // Verify old key is archived

     * Rotate a specific session key
     *
     * @param sessionId the session ID
     * @return the new key version number
     * @throws GeneralSecurityException if rotation fails
     */
    public int rotateSessionKey(String sessionId) throws GeneralSecurityException {
        checkNotClosed();

        if (!sessionKeys.containsKey(sessionId)) {
            throw new IllegalArgumentException("Session key not found: " + sessionId);