Load complete chat history when reaching the top (#2481)

* fix(chat): load older timeline history consistently

Pagination depended on scroll events, so short or compacted initial pages could never request older history. Reevaluate edge visibility as layout and history change, and standardize loading indicators on the canonical app spinner.

* fix(chat): keep older history loading reliably

Use authoritative timeline cursor progress so merged rows cannot stall pagination. Wait for bottom anchoring before evaluating the history edge, and re-arm retries on a fresh upward gesture without automatic failure loops.

packages/app/e2e/helpers/agent-timeline-gate.ts

@@ -10,6 +10,11 @@ interface CreatedAgentTimelineGate {
   waitForForwardedResponse(): Promise<void>;
 }
 
+export interface AgentTimelineResponseGate {
+  release(): void;
+  waitForDelayedResponse(): Promise<void>;
+}
+
 function parseWebSocketJson(message: WebSocketMessage): unknown {
   const rawMessage = typeof message === "string" ? message : message.toString("utf8");
   try {
@@ -118,3 +123,53 @@ export async function delayCreatedAgentInitialTailResponse(
     waitForForwardedResponse: () => forwardedResponse,
   };
 }
+
+export async function delayAgentOlderTimelineResponse(
+  page: Page,
+  agentId: string,
+): Promise<AgentTimelineResponseGate> {
+  let releaseRequested = false;
+  let delayedResponseSeen = false;
+  const delayedForwards: Array<() => void> = [];
+  let resolveDelayedResponse: (() => void) | null = null;
+  const delayedResponse = new Promise<void>((resolve) => {
+    resolveDelayedResponse = resolve;
+  });
+
+  await page.routeWebSocket(daemonWsRoutePattern(), (ws) => {
+    const server = ws.connectToServer();
+    ws.onMessage((message) => {
+      server.send(message);
+    });
+    server.onMessage((message) => {
+      const sessionMessage = getSessionMessage(message);
+      const payload = sessionMessage ? getPayload(sessionMessage) : null;
+      if (
+        !delayedResponseSeen &&
+        sessionMessage?.type === "fetch_agent_timeline_response" &&
+        payload?.agentId === agentId &&
+        payload.direction === "before"
+      ) {
+        delayedResponseSeen = true;
+        resolveDelayedResponse?.();
+        if (releaseRequested) {
+          ws.send(message);
+          return;
+        }
+        delayedForwards.push(() => ws.send(message));
+        return;
+      }
+      ws.send(message);
+    });
+  });
+
+  return {
+    release() {
+      releaseRequested = true;
+      for (const forward of delayedForwards.splice(0)) {
+        forward();
+      }
+    },
+    waitForDelayedResponse: () => delayedResponse,
+  };
+}