{# What an htmx request gets instead of the shell: the page's
   ``app_content`` block and nothing else, ready to swap into
   ``#app-content``. A page template picks this or ``app_shell.html`` via
   ``{% extends layout %}``; the render helper (P1.4) sets ``layout`` from
   the ``HX-Request`` header. #}
{%- block app_content %}{% endblock -%}