fix(app): paginate canonical timeline catch-up to avoid relay 1009 disconnect loop (#657)

@fireblue diagnosed the production failure mode: long canonical timeline catch-up could exceed the relay WebSocket frame cap, close with 1009, and send clients into a reconnect loop. Their seatbelt fix also removed the `limit: 0` footgun that let app callers request an unbounded frame.

This maintainer pass keeps that diagnosis and redirects the UX around bounded projected pages:

- initial agent load fetches the latest canonical tail
- app resume/reconnect re-fetches the latest tail instead of chaining after-cursor pages
- in-stream gaps still use bounded after-cursor catch-up
- older history loads explicitly when the user scrolls to the oldest edge
- shared page size is TIMELINE_FETCH_PAGE_SIZE = 100 projected timeline items, matching the daemon's canonical projection semantics rather than raw delta chunks

Original diagnosis and fix by @fireblue.

Co-authored-by: Mohamed Boudra <boudra.moha@gmail.com>

packages/app/src/hooks/use-agent-initialization.ts

@@ -8,21 +8,9 @@ import {
   getInitKey,
   rejectInitDeferred,
 } from "@/utils/agent-initialization";
-import { deriveInitialTimelineRequest } from "@/contexts/session-timeline-bootstrap-policy";
-import { isWeb } from "@/constants/platform";
+import { TIMELINE_FETCH_PAGE_SIZE } from "@/timeline/timeline-fetch-policy";
 
 const INIT_TIMEOUT_MS = 5 * 60_000;
-const NATIVE_INITIAL_TIMELINE_LIMIT = 200;
-const UNBOUNDED_TIMELINE_LIMIT = 0;
-
-function resolveInitialTimelineLimit(): number {
-  return isWeb ? UNBOUNDED_TIMELINE_LIMIT : NATIVE_INITIAL_TIMELINE_LIMIT;
-}
-
-export const __private__ = {
-  deriveInitialTimelineRequest,
-  resolveInitialTimelineLimit,
-};
 
 export function useAgentInitialization({
   serverId,
@@ -54,19 +42,13 @@ export function useAgentInitialization({
         return existing.promise;
       }
 
-      const session = useSessionStore.getState().sessions[serverId];
-      const cursor = session?.agentTimelineCursor.get(agentId);
-      const initialTimelineLimit = resolveInitialTimelineLimit();
-      const hasAuthoritativeHistory =
-        session?.agentAuthoritativeHistoryApplied.get(agentId) === true;
-      const timelineRequest = deriveInitialTimelineRequest({
-        cursor: cursor ? { epoch: cursor.epoch, seq: cursor.endSeq } : null,
-        hasAuthoritativeHistory,
-        initialTimelineLimit,
-      });
-      const initRequestDirection = timelineRequest.direction === "after" ? "after" : "tail";
+      const timelineRequest = {
+        direction: "tail" as const,
+        limit: TIMELINE_FETCH_PAGE_SIZE,
+        projection: "canonical" as const,
+      };
 
-      const deferred = createInitDeferred(key, initRequestDirection);
+      const deferred = createInitDeferred(key, "tail");
       const timeoutId = setTimeout(() => {
         setAgentInitializing(agentId, false);
         rejectInitDeferred(
@@ -103,10 +85,9 @@ export function useAgentInitialization({
 
       try {
         await client.refreshAgent(agentId);
-        const initialTimelineLimit = resolveInitialTimelineLimit();
         await client.fetchAgentTimeline(agentId, {
           direction: "tail",
-          limit: initialTimelineLimit,
+          limit: TIMELINE_FETCH_PAGE_SIZE,
           projection: "canonical",
         });
       } catch (error) {