long overdue fix to last pipeline push, where scroll position did not persist across sessions

src/templates/apps/billboard/_partials/_applet-billboard-scroll.html

@@ -22,8 +22,12 @@
             }
         }
 
-        // Restore: position stored is bottom-of-viewport; subtract clientHeight to align it
-        scroll.scrollTop = Math.max(0, {{ scroll_position }} - scroll.clientHeight);
+        // Only restore if there's a meaningful saved position — avoids a
+        // no-op scrollTop assignment (0→0) that can fire a spurious scroll
+        // event and reset the debounce timer in tests / headless browsers.
+        if ({{ scroll_position }} > 0) {
+            scroll.scrollTop = Math.max(0, {{ scroll_position }} - scroll.clientHeight);
+        }
     });
 
     // Animate "What happens next. . . ?" buffer dots — 4th span shows '?'
@@ -37,21 +41,24 @@
         }, 400);
     }
 
-    // Debounced save on scroll — store bottom-of-viewport so the last-read line is restored
+    // Debounced save on scroll — store bottom-of-viewport so the last-read line is restored.
+    // Position is captured at event time so layout changes during the debounce window
+    // (e.g. rAF adjusting marginTop) don't produce a stale clientHeight.
+    var remPx = parseFloat(getComputedStyle(document.documentElement).fontSize);
     var saveTimer;
     scroll.addEventListener('scroll', function() {
+        var pos = Math.round(scroll.scrollTop + scroll.clientHeight + remPx * 2.5);
         clearTimeout(saveTimer);
         saveTimer = setTimeout(function() {
             var csrfToken = document.querySelector('[name=csrfmiddlewaretoken]');
             var token = csrfToken ? csrfToken.value : '';
-            var remPx = parseFloat(getComputedStyle(document.documentElement).fontSize);
             fetch("{% url 'billboard:save_scroll_position' room.id %}", {
                 method: 'POST',
                 headers: {
                     'Content-Type': 'application/x-www-form-urlencoded',
                     'X-CSRFToken': token,
                 },
-                body: 'position=' + Math.round(scroll.scrollTop + scroll.clientHeight + remPx * 2.5),
+                body: 'position=' + pos,
             });
         }, 800);
     });