From 7b0d5e863439b9efaae44cfce1a4a467ab966acc Mon Sep 17 00:00:00 2001
From: Craig Constable <craig@codezeno.com.au>
Date: Sun, 15 Mar 2026 17:37:38 +1000
Subject: [PATCH] fix(web): preserve scroll when collapsing large changed-files
 trees

---
 apps/web/src/components/chat/ChangedFilesTree.tsx | 1 +
 apps/web/src/components/chat/MessagesTimeline.tsx | 8 +++++++-
 2 files changed, 8 insertions(+), 1 deletion(-)

diff --git a/apps/web/src/components/chat/ChangedFilesTree.tsx b/apps/web/src/components/chat/ChangedFilesTree.tsx
index 0174a7708..a13ddad30 100644
--- a/apps/web/src/components/chat/ChangedFilesTree.tsx
+++ b/apps/web/src/components/chat/ChangedFilesTree.tsx
@@ -50,6 +50,7 @@ export const ChangedFilesTree = memo(function ChangedFilesTree(props: {
         <div key={`dir:${node.path}`}>
           <button
             type="button"
+            data-scroll-anchor-ignore
             className="group flex w-full items-center gap-1.5 rounded-md py-1 pr-2 text-left hover:bg-background/80"
             style={{ paddingLeft: `${leftPadding}px` }}
             onClick={() => toggleDirectory(node.path, depth === 0)}
diff --git a/apps/web/src/components/chat/MessagesTimeline.tsx b/apps/web/src/components/chat/MessagesTimeline.tsx
index e30801041..fcc8f697a 100644
--- a/apps/web/src/components/chat/MessagesTimeline.tsx
+++ b/apps/web/src/components/chat/MessagesTimeline.tsx
@@ -245,9 +245,14 @@ export const MessagesTimeline = memo(function MessagesTimeline({
     rowVirtualizer.measure();
   }, [rowVirtualizer, timelineWidthPx]);
   useEffect(() => {
-    rowVirtualizer.shouldAdjustScrollPositionOnItemSizeChange = (_item, _delta, instance) => {
+    rowVirtualizer.shouldAdjustScrollPositionOnItemSizeChange = (item, _delta, instance) => {
       const viewportHeight = instance.scrollRect?.height ?? 0;
       const scrollOffset = instance.scrollOffset ?? 0;
+      const itemIntersectsViewport =
+        item.end > scrollOffset && item.start < scrollOffset + viewportHeight;
+      if (itemIntersectsViewport) {
+        return false;
+      }
       const remainingDistance = instance.getTotalSize() - (scrollOffset + viewportHeight);
       return remainingDistance > AUTO_SCROLL_BOTTOM_THRESHOLD_PX;
     };
@@ -458,6 +463,7 @@ export const MessagesTimeline = memo(function MessagesTimeline({
                             type="button"
                             size="xs"
                             variant="outline"
+                            data-scroll-anchor-ignore
                             onClick={() => onToggleAllDirectories(turnSummary.turnId)}
                           >
                             {allDirectoriesExpanded ? "Collapse all" : "Expand all"}