scroll position save fix attempt no. 1 feat. 'What happens next…?' text at bottom of scroll; buffer added to scroll, accounter for in FTs

src/functional_tests/test_billboard.py

@@ -154,15 +154,17 @@ class BillscrollPositionTest(FunctionalTest):
         )
 
         # 2. Force the element scrollable (CSS not served by StaticLiveServerTestCase),
-        #    set position, and dispatch scroll event to trigger the debounced save
-        target = 100
+        #    set position, and dispatch scroll event to trigger the debounced save.
+        #    JS saves scrollTop + clientHeight (bottom-of-viewport); forced height is 150px.
+        scroll_top = 100
+        forced_height = 150
         self.browser.execute_script("""
             var el = arguments[0];
             el.style.overflow = 'auto';
             el.style.height = '150px';
             el.scrollTop = arguments[1];
             el.dispatchEvent(new Event('scroll'));
-        """, scroll_el, target)
+        """, scroll_el, scroll_top)
 
         # 3. Wait for debounce (800ms) + fetch to complete
         time.sleep(3)
@@ -178,8 +180,11 @@ class BillscrollPositionTest(FunctionalTest):
         scroll_el = self.wait_for(
             lambda: self.browser.find_element(By.ID, "id_drama_scroll")
         )
+        buffer_px = self.browser.execute_script(
+            "return Math.round(parseFloat(getComputedStyle(document.documentElement).fontSize) * 2.5)"
+        )
         restored = int(scroll_el.get_attribute("data-scroll-position"))
-        self.assertEqual(restored, target)
+        self.assertEqual(restored, scroll_top + forced_height + buffer_px)
 
 
 class BillboardAppletsTest(FunctionalTest):