diff --git a/assets/app.js b/assets/app.js
index e56396c..3cb7ffc 100644
--- a/assets/app.js
+++ b/assets/app.js
@@ -1,10 +1,25 @@
 import './stimulus_bootstrap.js';
-/*
- * Welcome to your app's main JavaScript file!
- *
- * This file will be included onto the page via the importmap() Twig function,
- * which should already be in your base.html.twig.
- */
 import './styles/app.css';
 
-console.log('This log comes from assets/app.js - welcome to AssetMapper! 🎉');
+import htmx from 'htmx.org';
+
+// Exposed so inline `hx-on:` handlers and Stimulus controllers can reach htmx.
+window.htmx = htmx;
+
+// We never return <script> tags in fragments; refuse to run them if one slips through.
+htmx.config.allowScriptTags = false;
+// Indicators are styled in Tailwind, not by htmx's injected <style> block.
+htmx.config.includeIndicatorStyles = false;
+
+// AbstractController::render() returns 422 when it is handed an invalid submitted form, and
+// htmx 2 does not swap 4xx by default -- so without this entry a failed validation would
+// silently do nothing and the modal would just sit there unchanged.
+// resolveResponseHandling() returns the FIRST matching entry, so 422 must precede the
+// [45].. catch-all. The other three entries are htmx's defaults, repeated because assigning
+// this config replaces the whole array.
+htmx.config.responseHandling = [
+    { code: '204', swap: false },
+    { code: '[23]..', swap: true },
+    { code: '422', swap: true, error: false },
+    { code: '[45]..', swap: false, error: true },
+];