fix: optimize agent stream rendering and timeline cursor updates

packages/app/src/components/agent-stream-view.tsx

@@ -636,6 +636,14 @@ export function AgentStreamView({
     ]
   );
 
+  // Keep maintainVisibleContentPosition shape and values stable to avoid
+  // reconfiguring RN's internal anchoring logic during streaming transitions.
+  // We rely on our own follow-tail logic, so keep threshold at 0.
+  const maintainVisibleContentPosition = useMemo(
+    () => ({ minIndexForVisible: 0, autoscrollToTopThreshold: 0 }),
+    []
+  );
+
   // FlatList's ListHeaderComponent renders at the *bottom* when inverted.
   // Without explicit spacing, the newest "head" rows (like Thinking/Setup tool badges)
   // can butt up directly against the most recent stream item.
@@ -712,12 +720,7 @@ export function AgentStreamView({
               ListEmptyComponent={listEmptyComponent}
               ListHeaderComponent={listHeaderComponent}
               extraData={flatListExtraData}
-              maintainVisibleContentPosition={
-                // Disable when streaming and user is at bottom - we handle auto-scroll ourselves
-                agent.status === "running" && isNearBottom
-                  ? undefined
-                  : { minIndexForVisible: 0, autoscrollToTopThreshold: 40 }
-              }
+              maintainVisibleContentPosition={maintainVisibleContentPosition}
               initialNumToRender={12}
               windowSize={10}
               scrollEnabled={Platform.OS !== "web" || expandedInlineToolCallIds.size === 0}

packages/app/src/contexts/session-context.tsx

@@ -803,16 +803,22 @@ function SessionProviderInternal({
       ) {
         setAgentTimelineCursor(serverId, (prev) => {
           const current = prev.get(agentId);
-          const next = new Map(prev);
-          if (!current || current.epoch !== epoch) {
-            next.set(agentId, { epoch, startSeq: seq, endSeq: seq });
+          if (current && current.epoch === epoch) {
+            // Fast-path: seq only extends the range during streaming.
+            // Skip the Map copy when nothing actually changes.
+            if (seq >= current.startSeq && seq <= current.endSeq) {
+              return prev;
+            }
+            const next = new Map(prev);
+            next.set(agentId, {
+              epoch,
+              startSeq: Math.min(current.startSeq, seq),
+              endSeq: Math.max(current.endSeq, seq),
+            });
             return next;
           }
-          next.set(agentId, {
-            epoch,
-            startSeq: Math.min(current.startSeq, seq),
-            endSeq: Math.max(current.endSeq, seq),
-          });
+          const next = new Map(prev);
+          next.set(agentId, { epoch, startSeq: seq, endSeq: seq });
           return next;
         });
       }

packages/app/src/stores/session-store.ts

@@ -546,11 +546,15 @@ export const useSessionStore = create<SessionStore>()(
           return prev;
         }
         logSessionStoreUpdate("setFocusedAgentId", serverId, { agentId });
+
         return {
           ...prev,
           sessions: {
             ...prev.sessions,
-            [serverId]: { ...session, focusedAgentId: agentId },
+            [serverId]: {
+              ...session,
+              focusedAgentId: agentId,
+            },
           },
         };
       });
@@ -563,7 +567,8 @@ export const useSessionStore = create<SessionStore>()(
         if (!session) {
           return prev;
         }
-        const nextMessages = typeof messages === "function" ? messages(session.messages) : messages;
+        const nextMessages =
+          typeof messages === "function" ? messages(session.messages) : messages;
         if (session.messages === nextMessages) {
           return prev;
         }