From f62200ecd1c9bcc11e22c09c265390b73de24d35 Mon Sep 17 00:00:00 2001
From: litruv <litruv@gmail.com>
Date: Fri, 24 Jul 2026 16:00:54 +1000
Subject: [PATCH] Fix Jump to Latest sticking visible while scrolled to the
 live bottom.

---
 src/app/features/room/RoomTimeline.tsx | 35 +++++++++++++++++++++++---
 1 file changed, 32 insertions(+), 3 deletions(-)

diff --git a/src/app/features/room/RoomTimeline.tsx b/src/app/features/room/RoomTimeline.tsx
index 8dd194e..996169b 100644
--- a/src/app/features/room/RoomTimeline.tsx
+++ b/src/app/features/room/RoomTimeline.tsx
@@ -785,9 +785,16 @@ export function RoomTimeline({ room, eventId, roomInputRef, editor }: RoomTimeli
   atLiveEndRef.current = liveTimelineLinked && rangeAtEnd;
 
   // Historical / non-live windows are never "at bottom" of the room.
+  // When we return to the live end, re-check scroll — IntersectionObserver may
+  // not re-fire if the anchor stayed intersecting across the transition.
   useEffect(() => {
     if (!liveTimelineLinked || !rangeAtEnd) {
       setAtBottom(false);
+      return;
+    }
+    const scrollEl = scrollRef.current;
+    if (scrollEl && isScrolledToBottom(scrollEl, 100)) {
+      setAtBottom(true);
     }
   }, [liveTimelineLinked, rangeAtEnd]);
 
@@ -1034,11 +1041,16 @@ export function RoomTimeline({ room, eventId, roomInputRef, editor }: RoomTimeli
         if (!targetEntry) return;
 
         // Leave the live bottom immediately so Jump to Latest stays available.
-        if (!targetEntry.isIntersecting || !atLiveEndRef.current) {
+        // Only intersection clears atBottom here; !atLiveEnd is handled by the
+        // liveTimelineLinked/rangeAtEnd effect so we don't stick false when the
+        // live end reconnects without a new intersection event.
+        if (!targetEntry.isIntersecting) {
           setAtBottom(false);
           return;
         }
 
+        if (!atLiveEndRef.current) return;
+
         setAtBottom(true);
         setLatestUnreadMessage(null);
         if (document.hasFocus()) {
@@ -1145,7 +1157,16 @@ export function RoomTimeline({ room, eventId, roomInputRef, editor }: RoomTimeli
     const onScroll = () => {
       if (restoringScrollRef.current) return;
       window.cancelAnimationFrame(raf);
-      raf = window.requestAnimationFrame(() => persistTimelineScroll(roomId));
+      raf = window.requestAnimationFrame(() => {
+        persistTimelineScroll(roomId);
+        // Keep Jump to Latest in sync with real scroll position when on the live end.
+        // IntersectionObserver alone can miss transitions and leave atBottom stuck.
+        if (atLiveEndRef.current) {
+          const at = isScrolledToBottom(scrollEl, 100);
+          setAtBottom(at);
+          if (at) setLatestUnreadMessage(null);
+        }
+      });
     };
 
     scrollEl.addEventListener('scroll', onScroll, { passive: true });
@@ -1250,6 +1271,9 @@ export function RoomTimeline({ room, eventId, roomInputRef, editor }: RoomTimeli
           scrollToBottomRef.current.smooth,
           scrollToBottomRef.current.force
         );
+        if (atLiveEndRef.current) {
+          setAtBottom(true);
+        }
       }
     }
   }, [scrollToBottomCount]);
@@ -2588,7 +2612,12 @@ export function RoomTimeline({ room, eventId, roomInputRef, editor }: RoomTimeli
                 </MessageBase>
               </>
             ))}
-          <span ref={atBottomAnchorRef} />
+          {/* 1×1 so IntersectionObserver reliably detects the live bottom */}
+          <span
+            ref={atBottomAnchorRef}
+            aria-hidden
+            style={{ display: 'block', width: 1, height: 1 }}
+          />
         </Box>
       </Scroll>
       {(showUnreadTop || returnToEventId) && (