Resume cached timelines without replaying their tail (#3329)

* perf(timeline): resume cached history from its exact range

Warm launches were repainting cached history and then downloading the same bounded tail to rediscover that nothing changed. Persist synchronization authority only when the complete current canonical window can be encoded losslessly; otherwise retain the existing display-only fallback.

* test(timeline): hide replica setup behind E2E helper

* fix(timeline): bound persisted resume overflow

* test(timeline): cover workspace eviction catch-up order

* test(timeline): read persisted range from IndexedDB

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

@@ -31,6 +31,82 @@ export interface PromptJumpRequestTracker {
   requests(): Array<{ cursorSeq: number | null; limit: number | null; mergeWindow: boolean }>;
 }
 
+export interface TimelineRequestTracker {
+  nextRequest(): Promise<{
+    direction: string | null;
+    cursor: { epoch: string; seq: number } | null;
+  }>;
+  requests(): Array<{
+    direction: string | null;
+    cursor: { epoch: string; seq: number } | null;
+  }>;
+  waitForResponse(): Promise<void>;
+}
+
+export async function trackAgentTimelineRequests(
+  page: Page,
+  agentId: string,
+): Promise<TimelineRequestTracker> {
+  type Request = ReturnType<TimelineRequestTracker["requests"]>[number];
+  const seen: Request[] = [];
+  const waiters: Array<(request: Request) => void> = [];
+  let responseSeen = false;
+  let resolveResponse: (() => void) | null = null;
+  const response = new Promise<void>((resolve) => {
+    resolveResponse = resolve;
+  });
+  await page.routeWebSocket(daemonWsRoutePattern(), (ws) => {
+    const server = ws.connectToServer();
+    ws.onMessage((message) => {
+      const sessionMessage = getSessionMessage(message);
+      if (
+        sessionMessage?.type === "fetch_agent_timeline_request" &&
+        sessionMessage.agentId === agentId
+      ) {
+        const rawCursor = sessionMessage.cursor;
+        const cursor =
+          rawCursor &&
+          typeof rawCursor === "object" &&
+          typeof (rawCursor as { epoch?: unknown }).epoch === "string" &&
+          typeof (rawCursor as { seq?: unknown }).seq === "number"
+            ? {
+                epoch: (rawCursor as { epoch: string }).epoch,
+                seq: (rawCursor as { seq: number }).seq,
+              }
+            : null;
+        const request = {
+          direction: typeof sessionMessage.direction === "string" ? sessionMessage.direction : null,
+          cursor,
+        };
+        seen.push(request);
+        waiters.shift()?.(request);
+      }
+      server.send(message);
+    });
+    server.onMessage((message) => {
+      const sessionMessage = getSessionMessage(message);
+      const payload = sessionMessage ? getPayload(sessionMessage) : null;
+      if (
+        sessionMessage?.type === "fetch_agent_timeline_response" &&
+        payload?.agentId === agentId
+      ) {
+        responseSeen = true;
+        resolveResponse?.();
+      }
+      ws.send(message);
+    });
+  });
+  return {
+    nextRequest() {
+      const request = seen[0];
+      if (request) return Promise.resolve(request);
+      return new Promise((resolve) => waiters.push(resolve));
+    },
+    requests: () => [...seen],
+    waitForResponse: () => (responseSeen ? Promise.resolve() : response),
+  };
+}
+
 export async function trackPromptJumpRequests(
   page: Page,
   agentId: string,