Better

assets/templates/notice.njk

@@ -0,0 +1,12 @@
+{# A page that could not be delivered, written in the same shape as a real
+   one: a title and one root element naming the template that wraps it.
+
+   Sent with 200 on purpose. htmx only swaps a 2xx body, and an error status
+   would leave the reader looking at the page they came from with nothing to
+   say what happened. #}
+<title>{{ heading }}</title>
+<div class="notice" data-template="page">
+  <h1>{{ heading }}</h1>
+  <p>{{ text }}</p>
+  <p><a href="./">All books</a></p>
+</div>