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/stores/session-store.ts

@@ -268,6 +268,8 @@ export interface SessionState {
   agentStreamTail: Map<string, StreamItem[]>;
   agentStreamHead: Map<string, StreamItem[]>;
   agentTimelineCursor: Map<string, AgentTimelineCursorState>;
+  agentTimelineHasOlder: Map<string, boolean>;
+  agentTimelineOlderFetchInFlight: Map<string, boolean>;
   historySyncGeneration: number;
   agentHistorySyncGeneration: Map<string, number>;
   agentAuthoritativeHistoryApplied: Map<string, boolean>;
@@ -351,6 +353,14 @@ interface SessionStoreActions {
       | Map<string, AgentTimelineCursorState>
       | ((prev: Map<string, AgentTimelineCursorState>) => Map<string, AgentTimelineCursorState>),
   ) => void;
+  setAgentTimelineHasOlder: (
+    serverId: string,
+    state: Map<string, boolean> | ((prev: Map<string, boolean>) => Map<string, boolean>),
+  ) => void;
+  setAgentTimelineOlderFetchInFlight: (
+    serverId: string,
+    state: Map<string, boolean> | ((prev: Map<string, boolean>) => Map<string, boolean>),
+  ) => void;
   bumpHistorySyncGeneration: (serverId: string) => void;
   markAgentHistorySynchronized: (serverId: string, agentId: string) => void;
   setAgentAuthoritativeHistoryApplied: (
@@ -443,6 +453,8 @@ function createInitialSessionState(serverId: string, client: DaemonClient): Sess
     agentStreamTail: new Map(),
     agentStreamHead: new Map(),
     agentTimelineCursor: new Map(),
+    agentTimelineHasOlder: new Map(),
+    agentTimelineOlderFetchInFlight: new Map(),
     historySyncGeneration: 0,
     agentHistorySyncGeneration: new Map(),
     agentAuthoritativeHistoryApplied: new Map(),
@@ -861,6 +873,48 @@ export const useSessionStore = create<SessionStore>()(
         });
       },
 
+      setAgentTimelineHasOlder: (serverId, state) => {
+        set((prev) => {
+          const session = prev.sessions[serverId];
+          if (!session) {
+            return prev;
+          }
+          const nextState =
+            typeof state === "function" ? state(session.agentTimelineHasOlder) : state;
+          if (session.agentTimelineHasOlder === nextState) {
+            return prev;
+          }
+          return {
+            ...prev,
+            sessions: {
+              ...prev.sessions,
+              [serverId]: { ...session, agentTimelineHasOlder: nextState },
+            },
+          };
+        });
+      },
+
+      setAgentTimelineOlderFetchInFlight: (serverId, state) => {
+        set((prev) => {
+          const session = prev.sessions[serverId];
+          if (!session) {
+            return prev;
+          }
+          const nextState =
+            typeof state === "function" ? state(session.agentTimelineOlderFetchInFlight) : state;
+          if (session.agentTimelineOlderFetchInFlight === nextState) {
+            return prev;
+          }
+          return {
+            ...prev,
+            sessions: {
+              ...prev.sessions,
+              [serverId]: { ...session, agentTimelineOlderFetchInFlight: nextState },
+            },
+          };
+        });
+      },
+
       bumpHistorySyncGeneration: (serverId) => {
         set((prev) => {
           const session = prev.sessions[serverId];