EDIT: Doing some digging, and it looks like my problem stems from the fact that the form I'm creating builds off of the FOSUserBundle's registration form. Why is that an issue? Because while their RegistrationController throws a REGISTRATION_FAILURE event if the form isn't valid, it doesn't look like the event has a listener. So, the invalid state doesn't actually do anything aside from not being handled at all by the system. It doesn't even return the form (with errors).
I have a relatively simple form theme I want to use in order to display my form errors in a block at the top of my form:
{% form_theme form _self %}
{% block form_errors %}
{% spaceless %}
{% if errors|length > 0 %}
<div class="errors pt-2 mb-2">
<ul>
{% for error in errors %}
<li>{{ error.message }}</li>
{% endfor %}
</ul>
</div>
{% endif %}
{% endspaceless %}
{% endblock form_errors %}
I reference it in the form template with:
{% form_theme form 'Form/errors.html.twig' %}
And then I try to invoke it with a simple:
{{ form_errors(form) }}
But, when I intentionally provide incorrect data to my form inputs and try to submit, there's no error div present. The submission fails, due to there being 6 validation errors, but no errors are displayed/in the HTML source.
Looking at the documentation, I think I'm doing it right, but I'm obviously missing something.