19 lines (16 with data), 663 Bytes

{% if messages[0]['role'] == 'system' %}
    {% set system_message = messages[0]['content'] | trim + '<|end_of_turn|>' %}
    {% set messages = messages[1:] %}
{% else %}
    {% set system_message = '' %}
{% endif %}

{{ bos_token + system_message }}
{% for message in messages %}
    {% if (message['role'] == 'user') != (loop.index0 % 2 == 0) %}
        {{ raise_exception('Conversation roles must alternate user/assistant/user/assistant/...') }}
    {% endif %}

    {{ 'GPT4 Correct ' + message['role'] | capitalize + ': ' + message['content'] + '<|end_of_turn|>' }}
{% endfor %}

{% if add_generation_prompt %}
    {{ 'GPT4 Correct Assistant:' }}
{% endif %}