fix(desktop): remount timeline scroll node per channel (#1147)

Signed-off-by: npub1t2tgm7d8f995uqvmnm8h88sg3wnpp9a5xysjf6dg3tjmgt3ltulqdp8ehr <5a968df9a7494b4e019b9ecf739e088ba61097b4312124e9a88ae5b42e3f5f3e@sprout-oss.stage.blox.sqprod.co>
Co-authored-by: npub1t2tgm7d8f995uqvmnm8h88sg3wnpp9a5xysjf6dg3tjmgt3ltulqdp8ehr <5a968df9a7494b4e019b9ecf739e088ba61097b4312124e9a88ae5b42e3f5f3e@sprout-oss.stage.blox.sqprod.co>

desktop/src/features/channels/ui/ChannelPane.tsx

@@ -264,7 +264,7 @@ export const ChannelPane = React.memo(function ChannelPane({
   useComposerHeightPadding(
     timelineScrollRef,
     composerWrapperRef,
-    `${isSinglePanelView}:${hasMainComposerOverlay}`,
+    `${activeChannelId}:${isSinglePanelView}:${hasMainComposerOverlay}`,
   );
 
   const clearWelcomeComposerDismissTimer = React.useCallback(() => {

desktop/src/features/messages/ui/MessageTimeline.tsx

@@ -205,6 +205,12 @@ const MessageTimelineBase = React.forwardRef<
   const scrollRestorationId = targetMessageId
     ? `message-timeline:${channelId ?? "none"}:target:${targetMessageId}`
     : `message-timeline:${channelId ?? "none"}`;
+  // Keep the scroll node's DOM lifetime scoped to a channel. TanStack Router's
+  // scroll-restoration listener runs outside React and may write a saved
+  // scrollTop into the current scroll element during navigation; reusing the
+  // same node across channel routes can leave the newly-loaded message list
+  // painted at a stale offset until the user's next scroll event forces layout.
+  const scrollContainerDomKey = channelId ?? "none";
 
   const timelineBodySurface = selectTimelineBodySurface({
     deferredCount: deferredMessages.length,
@@ -339,6 +345,7 @@ const MessageTimelineBase = React.forwardRef<
           )}
           data-scroll-restoration-id={scrollRestorationId}
           data-testid="message-timeline"
+          key={scrollContainerDomKey}
           onScroll={onScroll}
           ref={scrollContainerRef}
         >