fix(ui): Timeline uses EventFeed's internal scroll + load-older button

EventFeed has its own search + filter toolbar inside the component.
Wrapping it in InfiniteScrollArea made the toolbar scroll out of
sight. Drop InfiniteScrollArea for the Timeline, give EventFeed a
bounded-height flex container (it scrolls its own .list internally),
and add an explicit 'Load older events' button for cursor
pagination. Polling always on for events (low volume).

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

ui/src/pages/AgentInstance/AgentInstance.tsx

@@ -42,15 +42,13 @@ export default function AgentInstance() {
   const [logSortAsc, setLogSortAsc] = useState(false);
   const [eventSortAsc, setEventSortAsc] = useState(false);
   const [isLogAtTop, setIsLogAtTop] = useState(true);
-  const [isTimelineAtTop, setIsTimelineAtTop] = useState(true);
   const logScrollRef = useRef<HTMLDivElement | null>(null);
-  const timelineScrollRef = useRef<HTMLDivElement | null>(null);
   const timeFrom = timeRange.start.toISOString();
   const timeTo = timeRange.end.toISOString();
 
   const selectedEnv = useEnvironmentStore((s) => s.environment);
   const { data: agents, isLoading } = useAgents(undefined, appId);
-  const eventStream = useInfiniteAgentEvents({ appId, agentId: instanceId, isAtTop: isTimelineAtTop });
+  const eventStream = useInfiniteAgentEvents({ appId, agentId: instanceId, isAtTop: true });
 
   const agent = useMemo(
     () => (agents || []).find((a: any) => a.instanceId === instanceId) as any,
@@ -491,32 +489,29 @@ export default function AgentInstance() {
               <button className={logStyles.sortBtn} onClick={() => setEventSortAsc((v) => !v)} title={eventSortAsc ? 'Oldest first' : 'Newest first'}>
                 {eventSortAsc ? '\u2191' : '\u2193'}
               </button>
-              <button className={logStyles.refreshBtn} onClick={() => {
-                eventStream.refresh();
-                timelineScrollRef.current?.scrollTo({ top: 0 });
-              }} title="Refresh">
+              <button className={logStyles.refreshBtn} onClick={() => eventStream.refresh()} title="Refresh">
                 <RefreshCw size={14} />
               </button>
             </div>
           </div>
-          <InfiniteScrollArea
-            scrollRef={timelineScrollRef}
-            onEndReached={eventStream.fetchNextPage}
-            onTopVisibilityChange={setIsTimelineAtTop}
-            isFetchingNextPage={eventStream.isFetchingNextPage}
-            hasNextPage={eventStream.hasNextPage}
-            isLoading={eventStream.isLoading}
-            hasItems={eventStream.items.length > 0}
-            maxHeight={360}
-          >
+          <div className={logStyles.eventFeedContainer}>
             {feedEvents.length > 0 ? (
-              <EventFeed events={feedEvents} className={logStyles.flatScroll} />
+              <EventFeed events={feedEvents} />
             ) : (
               <div className={logStyles.logEmpty}>
                 {eventStream.isLoading ? 'Loading events…' : 'No events in the selected time range.'}
               </div>
             )}
-          </InfiniteScrollArea>
+          </div>
+          {eventStream.hasNextPage && (
+            <button
+              className={logStyles.loadOlderBtn}
+              onClick={eventStream.fetchNextPage}
+              disabled={eventStream.isFetchingNextPage}
+            >
+              {eventStream.isFetchingNextPage ? 'Loading…' : 'Load older events'}
+            </button>
+          )}
         </div>
       </div>
     </div>