Fix chat history paging around tool updates (#1247)

* Fix projected timeline paging

* Avoid full timeline fetches for plain pages

docs/timeline-sync.md

@@ -2,8 +2,8 @@
 
 Agent chat delivery has two paths:
 
-1. **Live stream** — `agent_stream` WebSocket messages for immediacy.
-2. **Authoritative history** — `fetch_agent_timeline_request` for correctness.
+1. **Live stream** — `agent_stream` WebSocket messages for immediacy. These may be delta-shaped lifecycle updates.
+2. **Authoritative history** — `fetch_agent_timeline_request` for correctness. This always returns full projected timeline items, never lifecycle deltas.
 
 The invariant is:
 
@@ -24,6 +24,8 @@ Heartbeat is used for notification routing. It must not be used as a correctness
 
 Large unbounded timeline responses can exceed relay frame limits, so catch-up uses bounded pages. Bounded does not mean partial.
 
+Page limits are projected-item targets. A tool call lifecycle is one projected item even if it spans many source sequence numbers, and assistant/reasoning chunks are merged before counting. The response carries `seqStart`, `seqEnd`, `sourceSeqRanges`, and `collapsed` so clients can advance sequence cursors without rendering delta rows.
+
 When the app fetches `direction: "after"` and the daemon responds with `hasNewer: true`, the app must immediately fetch the next page from `endCursor`. The catch-up is complete only when `hasNewer: false`.
 
 The first load of an agent without a local cursor is different: it fetches a bounded latest tail page. Older history remains user-driven by scrolling upward.

packages/app/e2e/helpers/rewind-flow.ts

@@ -320,12 +320,12 @@ async function fetchTimelineEpoch(handle: AgentHandle): Promise<string | undefin
   const client = handle.client as SeedDaemonClient & {
     fetchAgentTimeline: (
       agentId: string,
-      options?: { direction?: "head" | "tail"; projection?: "canonical"; limit?: number },
+      options?: { direction?: "head" | "tail"; projection?: "projected"; limit?: number },
     ) => Promise<{ epoch?: string }>;
   };
   const timeline = await client.fetchAgentTimeline(handle.agentId, {
     direction: "tail",
-    projection: "canonical",
+    projection: "projected",
     limit: 0,
   });
   return timeline.epoch;

packages/app/src/components/rewind/use-rewind-agent-mutation.ts

@@ -47,7 +47,7 @@ export function useRewindAgentMutation(input: UseRewindAgentMutationInput): {
           : undefined;
         await input.client.fetchAgentTimeline(input.agentId, {
           direction: "tail",
-          projection: "canonical",
+          projection: "projected",
           ...(cursor ? { cursor: { epoch: cursor.epoch, seq: cursor.endSeq } } : {}),
         });
       }

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

@@ -34,7 +34,7 @@ afterEach(() => {
 });
 
 describe("ensureAgentIsInitialized", () => {
-  it("requests bounded canonical catch-up after the current cursor when authoritative history is loaded", () => {
+  it("requests bounded projected catch-up after the current cursor when authoritative history is loaded", () => {
     const client = makeClient();
     useSessionStore.getState().initializeSession(serverId, client as never);
     useSessionStore
@@ -56,12 +56,12 @@ describe("ensureAgentIsInitialized", () => {
       direction: "after",
       cursor: { epoch: "epoch-1", seq: 42 },
       limit: TIMELINE_FETCH_PAGE_SIZE,
-      projection: "canonical",
+      projection: "projected",
     });
     expect(getInitDeferred(getInitKey(serverId, agentId))?.requestDirection).toBe("after");
   });
 
-  it("requests a bounded canonical tail when no authoritative cursor is available", () => {
+  it("requests a bounded projected tail when no authoritative cursor is available", () => {
     const client = makeClient();
     useSessionStore.getState().initializeSession(serverId, client as never);
 
@@ -75,7 +75,7 @@ describe("ensureAgentIsInitialized", () => {
     expect(client.fetchAgentTimeline).toHaveBeenCalledWith(agentId, {
       direction: "tail",
       limit: TIMELINE_FETCH_PAGE_SIZE,
-      projection: "canonical",
+      projection: "projected",
     });
     expect(getInitDeferred(getInitKey(serverId, agentId))?.requestDirection).toBe("tail");
   });
@@ -107,7 +107,7 @@ describe("ensureAgentIsInitialized", () => {
 });
 
 describe("refreshAgent", () => {
-  it("fetches a bounded canonical tail after refreshing the agent", async () => {
+  it("fetches a bounded projected tail after refreshing the agent", async () => {
     const client = makeClient();
     useSessionStore.getState().initializeSession(serverId, client as never);
 
@@ -121,7 +121,7 @@ describe("refreshAgent", () => {
     expect(client.fetchAgentTimeline).toHaveBeenCalledWith(agentId, {
       direction: "tail",
       limit: TIMELINE_FETCH_PAGE_SIZE,
-      projection: "canonical",
+      projection: "projected",
     });
   });
 });

packages/app/src/hooks/use-load-older-agent-history.test.ts

@@ -147,7 +147,7 @@ describe("loadOlderAgentHistory", () => {
           direction: "before",
           cursor: { epoch: "epoch-1", seq: 10 },
           limit: TIMELINE_FETCH_PAGE_SIZE,
-          projection: "canonical",
+          projection: "projected",
         },
       },
     ]);

packages/app/src/hooks/use-load-older-agent-history.ts

@@ -10,7 +10,7 @@ export interface LoadOlderAgentHistoryClient {
       direction: "before";
       cursor: { epoch: string; seq: number };
       limit: number;
-      projection: "canonical";
+      projection: "projected";
     },
   ) => Promise<unknown>;
 }

packages/app/src/screens/workspace/workspace-screen.tsx

@@ -2465,7 +2465,7 @@ function WorkspaceScreenContent({
         const currentCursor = sessionState?.agentTimelineCursor.get(agentId);
         await client.fetchAgentTimeline(agentId, {
           direction: "tail",
-          projection: "canonical",
+          projection: "projected",
           ...(currentCursor
             ? { cursor: { epoch: currentCursor.epoch, seq: currentCursor.endSeq } }
             : {}),

packages/app/src/timeline/session-stream-reducers.test.ts

@@ -547,6 +547,153 @@ describe("processTimelineResponse", () => {
     });
   });
 
+  it("hydrates a fetched in-progress tool call as one item and streams the next update on top", () => {
+    const fetched = processTimelineResponse({
+      ...baseTimelineInput,
+      isInitializing: true,
+      hasActiveInitDeferred: true,
+      initRequestDirection: "tail",
+      payload: {
+        ...baseTimelineInput.payload,
+        direction: "tail",
+        epoch: "epoch-1",
+        startCursor: { seq: 10 },
+        endCursor: { seq: 250 },
+        entries: [
+          {
+            ...makeToolCallTimelineEntry(10, "call-1", "running", {
+              type: "read",
+              filePath: "/tmp/example.ts",
+            }),
+            seqEnd: 250,
+            sourceSeqRanges: [
+              { startSeq: 10, endSeq: 10 },
+              { startSeq: 250, endSeq: 250 },
+            ],
+            collapsed: ["tool_lifecycle"],
+          },
+        ],
+      },
+    });
+
+    expect(getAgentToolCalls(fetched.tail)).toHaveLength(1);
+    expect(fetched.cursor).toEqual({ epoch: "epoch-1", startSeq: 10, endSeq: 250 });
+
+    const streamed = processAgentStreamEvent({
+      ...baseStreamInput,
+      currentTail: fetched.tail,
+      currentHead: fetched.head,
+      currentCursor: fetched.cursor ?? undefined,
+      seq: 251,
+      epoch: "epoch-1",
+      event: {
+        type: "timeline",
+        provider: "claude",
+        item: {
+          type: "tool_call",
+          callId: "call-1",
+          name: "Read",
+          status: "completed",
+          detail: {
+            type: "read",
+            filePath: "/tmp/example.ts",
+          },
+          error: null,
+        },
+      } as AgentStreamEventPayload,
+    });
+
+    const tools = getAgentToolCalls(streamed.tail);
+    expect(tools).toHaveLength(1);
+    expect(tools[0]?.payload.data.status).toBe("completed");
+    expect(streamed.cursor).toEqual({ epoch: "epoch-1", startSeq: 10, endSeq: 251 });
+  });
+
+  it("accepts an after-page projected tool update whose item started before the cursor", () => {
+    const existingCursor: TimelineCursor = {
+      epoch: "epoch-1",
+      startSeq: 10,
+      endSeq: 249,
+    };
+    const runningTool = hydrateStreamState(
+      [
+        {
+          event: makeToolCallTimelineEvent("call-1"),
+          timestamp: new Date(1010),
+        },
+      ],
+      { source: "canonical" },
+    );
+
+    const result = processTimelineResponse({
+      ...baseTimelineInput,
+      currentTail: runningTool,
+      currentCursor: existingCursor,
+      payload: {
+        ...baseTimelineInput.payload,
+        direction: "after",
+        epoch: "epoch-1",
+        startCursor: { seq: 250 },
+        endCursor: { seq: 250 },
+        entries: [
+          {
+            ...makeToolCallTimelineEntry(10, "call-1", "completed", {
+              type: "read",
+              filePath: "/tmp/example.ts",
+            }),
+            seqEnd: 250,
+            sourceSeqRanges: [
+              { startSeq: 10, endSeq: 10 },
+              { startSeq: 250, endSeq: 250 },
+            ],
+            collapsed: ["tool_lifecycle"],
+          },
+        ],
+      },
+    });
+
+    const catchUp = result.sideEffects.find((effect) => effect.type === "catch_up");
+    const tools = getAgentToolCalls(result.tail);
+    expect(catchUp).toBeUndefined();
+    expect(tools).toHaveLength(1);
+    expect(tools[0]?.payload.data.status).toBe("completed");
+    expect(result.cursor).toEqual({ epoch: "epoch-1", startSeq: 10, endSeq: 250 });
+  });
+
+  it("replaces an active assistant head when after-page returns a full projected assistant item", () => {
+    const existingCursor: TimelineCursor = {
+      epoch: "epoch-1",
+      startSeq: 1,
+      endSeq: 3,
+    };
+    const currentHead = [makeAssistantItem("ABC")];
+
+    const result = processTimelineResponse({
+      ...baseTimelineInput,
+      currentHead,
+      currentCursor: existingCursor,
+      payload: {
+        ...baseTimelineInput.payload,
+        direction: "after",
+        epoch: "epoch-1",
+        startCursor: { seq: 4 },
+        endCursor: { seq: 5 },
+        entries: [
+          {
+            ...makeTimelineEntry(1, "ABCDE"),
+            seqEnd: 5,
+            sourceSeqRanges: [{ startSeq: 1, endSeq: 5 }],
+            collapsed: ["assistant_merge"],
+          },
+        ],
+      },
+    });
+
+    expect(getAssistantTexts(result.tail)).toEqual([]);
+    expect(getAssistantTexts(result.head)).toEqual(["ABCDE"]);
+    expect(result.cursor).toEqual({ epoch: "epoch-1", startSeq: 1, endSeq: 5 });
+  });
+
   it("detects gap and emits catch-up side effect", () => {
     const existingCursor: TimelineCursor = {
       epoch: "epoch-1",

packages/app/src/timeline/session-stream-reducers.ts

@@ -53,9 +53,16 @@ type SessionTimelineSeqCursor =
 
 type SessionTimelineSeqDecision = "accept" | "drop_stale" | "drop_epoch" | "gap" | "init";
 
+interface TimelineSeqRange {
+  startSeq: number;
+  endSeq: number;
+}
+
 interface TimelineResponseEntry {
   seqStart: number;
   seqEnd: number;
+  sourceSeqRanges?: TimelineSeqRange[];
+  collapsed?: string[];
   provider: string;
   item: Record<string, unknown>;
   timestamp: string;
@@ -96,6 +103,7 @@ export interface ProcessTimelineResponseOutput {
 interface TimelineUnit {
   seq: number;
   seqEnd: number;
+  sourceSeqRanges: TimelineSeqRange[];
   event: AgentStreamEventPayload;
   timestamp: Date;
 }
@@ -376,44 +384,56 @@ function acceptIncrementalTimelineUnits(args: {
   currentCursor: TimelineCursor | undefined;
 }): IncrementalAcceptResult {
   const { timelineUnits, payload, currentCursor } = args;
-  const acceptedUnits: TimelineUnit[] = [];
-  let cursor: TimelineCursor | undefined = currentCursor;
-  let gapCursor: { epoch: string; endSeq: number } | null = null;
+  const firstUnit = timelineUnits[0];
+  const lastUnit = timelineUnits[timelineUnits.length - 1];
+  const responseStartSeq = payload.startCursor?.seq ?? firstUnit?.seq;
+  const responseEndSeq = payload.endCursor?.seq ?? lastUnit?.seqEnd;
 
-  for (const unit of timelineUnits) {
-    const decision: SessionTimelineSeqDecision = classifySessionTimelineSeq({
-      cursor: cursor ? { epoch: cursor.epoch, endSeq: cursor.endSeq } : null,
-      epoch: payload.epoch,
-      seq: unit.seq,
-    });
-
-    if (decision === "gap") {
-      gapCursor = cursor ? { epoch: cursor.epoch, endSeq: cursor.endSeq } : null;
-      break;
-    }
-    if (decision === "drop_stale") {
-      if (cursor && unit.seqEnd > cursor.endSeq) {
-        gapCursor = { epoch: cursor.epoch, endSeq: cursor.endSeq };
-        break;
-      }
-      continue;
-    }
-    if (decision === "drop_epoch") {
-      continue;
-    }
-
-    acceptedUnits.push(unit);
-    if (decision === "init") {
-      cursor = { epoch: payload.epoch, startSeq: unit.seq, endSeq: unit.seqEnd };
-      continue;
-    }
-    if (!cursor) {
-      continue;
-    }
-    cursor = { ...cursor, endSeq: unit.seqEnd };
+  if (responseStartSeq === undefined || responseEndSeq === undefined) {
+    return { acceptedUnits: [], cursor: currentCursor, gapCursor: null };
   }
 
-  return { acceptedUnits, cursor, gapCursor };
+  if (!currentCursor) {
+    return {
+      acceptedUnits: timelineUnits,
+      cursor: { epoch: payload.epoch, startSeq: responseStartSeq, endSeq: responseEndSeq },
+      gapCursor: null,
+    };
+  }
+
+  if (currentCursor.epoch !== payload.epoch) {
+    return { acceptedUnits: [], cursor: currentCursor, gapCursor: null };
+  }
+
+  if (
+    (!payload.startCursor || !payload.endCursor) &&
+    responseStartSeq <= currentCursor.endSeq &&
+    responseEndSeq > currentCursor.endSeq
+  ) {
+    return {
+      acceptedUnits: [],
+      cursor: currentCursor,
+      gapCursor: { epoch: currentCursor.epoch, endSeq: currentCursor.endSeq },
+    };
+  }
+
+  if (responseEndSeq <= currentCursor.endSeq) {
+    return { acceptedUnits: [], cursor: currentCursor, gapCursor: null };
+  }
+
+  if (responseStartSeq > currentCursor.endSeq + 1) {
+    return {
+      acceptedUnits: [],
+      cursor: currentCursor,
+      gapCursor: { epoch: currentCursor.epoch, endSeq: currentCursor.endSeq },
+    };
+  }
+
+  return {
+    acceptedUnits: timelineUnits,
+    cursor: { ...currentCursor, endSeq: responseEndSeq },
+    gapCursor: null,
+  };
 }
 
 function acceptOlderTimelineUnits(args: {
@@ -426,16 +446,21 @@ function acceptOlderTimelineUnits(args: {
     return { acceptedUnits: [], cursor: currentCursor, gapCursor: null };
   }
 
-  const acceptedUnits = timelineUnits.filter((unit) => unit.seqEnd < currentCursor.startSeq);
-  if (acceptedUnits.length === 0) {
-    return { acceptedUnits, cursor: currentCursor, gapCursor: null };
+  const firstUnit = timelineUnits[0];
+  const lastUnit = timelineUnits[timelineUnits.length - 1];
+  const responseStartSeq = payload.startCursor?.seq ?? firstUnit?.seq;
+  const responseEndSeq = payload.endCursor?.seq ?? lastUnit?.seqEnd;
+  if (
+    responseStartSeq === undefined ||
+    responseEndSeq === undefined ||
+    responseEndSeq >= currentCursor.startSeq
+  ) {
+    return { acceptedUnits: [], cursor: currentCursor, gapCursor: null };
   }
 
-  const firstAccepted = acceptedUnits[0];
-  const startSeq = payload.startCursor?.seq ?? firstAccepted?.seq ?? currentCursor.startSeq;
   return {
-    acceptedUnits,
-    cursor: { ...currentCursor, startSeq },
+    acceptedUnits: timelineUnits,
+    cursor: { ...currentCursor, startSeq: responseStartSeq },
     gapCursor: null,
   };
 }
@@ -480,6 +505,32 @@ function mergePrependedCanonicalTail(olderTail: StreamItem[], currentTail: Strea
   ];
 }
 
+function replaceLiveAssistantWithProjectedText(params: {
+  head: StreamItem[];
+  event: AgentStreamEventPayload;
+  timestamp: Date;
+}): StreamItem[] | null {
+  const { head, event, timestamp } = params;
+  if (event.type !== "timeline" || event.item.type !== "assistant_message") {
+    return null;
+  }
+  const index = head.findLastIndex((item) => item.kind === "assistant_message");
+  const current = head[index];
+  if (!current || current.kind !== "assistant_message") {
+    return null;
+  }
+  if (!event.item.text.startsWith(current.text)) {
+    return null;
+  }
+  const next = [...head];
+  next[index] = {
+    ...current,
+    text: event.item.text,
+    timestamp,
+  };
+  return next;
+}
+
 function applyTimelineIncrementalPath(args: {
   timelineUnits: TimelineUnit[];
   payload: ProcessTimelineResponseInput["payload"];
@@ -523,6 +574,15 @@ function applyTimelineIncrementalPath(args: {
       nextTail = mergePrependedCanonicalTail(olderTail, currentTail);
     } else if (currentHead.length > 0) {
       for (const { event, timestamp } of acceptedUnits) {
+        const replacedHead = replaceLiveAssistantWithProjectedText({
+          head: nextHead,
+          event,
+          timestamp,
+        });
+        if (replacedHead) {
+          nextHead = replacedHead;
+          continue;
+        }
         const applied = applyStreamEvent({
           tail: nextTail,
           head: nextHead,
@@ -597,6 +657,10 @@ export function processTimelineResponse(
   const timelineUnits = payload.entries.map((entry) => ({
     seq: entry.seqStart,
     seqEnd: entry.seqEnd,
+    sourceSeqRanges:
+      entry.sourceSeqRanges && entry.sourceSeqRanges.length > 0
+        ? entry.sourceSeqRanges
+        : [{ startSeq: entry.seqStart, endSeq: entry.seqEnd }],
     event: {
       type: "timeline",
       provider: entry.provider,

packages/app/src/timeline/timeline-fetch-policy.ts

@@ -1,2 +1,3 @@
-// Count is projected timeline items, not delta chunks. The daemon's `selectTimelineWindowByProjectedLimit` interprets this against canonical entries: `assistant_merge`, `reasoning_merge`, and `tool_lifecycle`. Do not confuse this with raw stream deltas.
+// Count is projected timeline items, not delta chunks. Fetch responses never return
+// tool lifecycle deltas; `sourceSeqRanges` maps projected items back to source seqs.
 export const TIMELINE_FETCH_PAGE_SIZE = 100;

packages/app/src/timeline/timeline-sync-plan.test.ts

@@ -18,7 +18,7 @@ describe("timeline sync planning", () => {
     expect(plan).toEqual({
       direction: "tail",
       limit: TIMELINE_FETCH_PAGE_SIZE,
-      projection: "canonical",
+      projection: "projected",
     });
   });
 
@@ -32,7 +32,7 @@ describe("timeline sync planning", () => {
       direction: "after",
       cursor: { epoch: "epoch-1", seq: 42 },
       limit: TIMELINE_FETCH_PAGE_SIZE,
-      projection: "canonical",
+      projection: "projected",
     });
   });
 
@@ -45,7 +45,7 @@ describe("timeline sync planning", () => {
       direction: "after",
       cursor: { epoch: "epoch-1", seq: 100 },
       limit: TIMELINE_FETCH_PAGE_SIZE,
-      projection: "canonical",
+      projection: "projected",
     });
   });
 
@@ -55,7 +55,7 @@ describe("timeline sync planning", () => {
     expect(plan).toEqual({
       direction: "tail",
       limit: TIMELINE_FETCH_PAGE_SIZE,
-      projection: "canonical",
+      projection: "projected",
     });
   });
 
@@ -66,7 +66,7 @@ describe("timeline sync planning", () => {
       direction: "before",
       cursor: { epoch: "epoch-1", seq: 25 },
       limit: TIMELINE_FETCH_PAGE_SIZE,
-      projection: "canonical",
+      projection: "projected",
     });
   });
 
@@ -82,7 +82,7 @@ describe("timeline sync planning", () => {
       direction: "after",
       cursor: { epoch: "epoch-1", seq: 200 },
       limit: TIMELINE_FETCH_PAGE_SIZE,
-      projection: "canonical",
+      projection: "projected",
     });
   });
 

packages/app/src/timeline/timeline-sync-plan.ts

@@ -11,39 +11,39 @@ export interface AgentTimelineCursorRange {
   endSeq: number;
 }
 
-export interface CanonicalTimelineTailFetchPlan {
+export interface ProjectedTimelineTailFetchPlan {
   direction: "tail";
   limit: number;
-  projection: "canonical";
+  projection: "projected";
 }
 
-export interface CanonicalTimelineAfterFetchPlan {
+export interface ProjectedTimelineAfterFetchPlan {
   direction: "after";
   cursor: TimelineSyncCursor;
   limit: number;
-  projection: "canonical";
+  projection: "projected";
 }
 
-export interface CanonicalTimelineBeforeFetchPlan {
+export interface ProjectedTimelineBeforeFetchPlan {
   direction: "before";
   cursor: TimelineSyncCursor;
   limit: number;
-  projection: "canonical";
+  projection: "projected";
 }
 
-export type CanonicalTimelineFetchPlan =
-  | CanonicalTimelineTailFetchPlan
-  | CanonicalTimelineAfterFetchPlan
-  | CanonicalTimelineBeforeFetchPlan;
+export type ProjectedTimelineFetchPlan =
+  | ProjectedTimelineTailFetchPlan
+  | ProjectedTimelineAfterFetchPlan
+  | ProjectedTimelineBeforeFetchPlan;
 
-export type CanonicalTimelineForwardFetchPlan =
-  | CanonicalTimelineTailFetchPlan
-  | CanonicalTimelineAfterFetchPlan;
+export type ProjectedTimelineForwardFetchPlan =
+  | ProjectedTimelineTailFetchPlan
+  | ProjectedTimelineAfterFetchPlan;
 
 export function planInitialAgentTimelineSync(input: {
   cursor: AgentTimelineCursorRange | undefined;
   hasAuthoritativeHistory: boolean;
-}): CanonicalTimelineForwardFetchPlan {
+}): ProjectedTimelineForwardFetchPlan {
   if (input.hasAuthoritativeHistory && input.cursor) {
     return planTimelineCatchUpAfter({ epoch: input.cursor.epoch, seq: input.cursor.endSeq });
   }
@@ -53,7 +53,7 @@ export function planInitialAgentTimelineSync(input: {
 
 export function planResumeTimelineSync(input: {
   cursor: AgentTimelineCursorRange | undefined;
-}): CanonicalTimelineForwardFetchPlan {
+}): ProjectedTimelineForwardFetchPlan {
   if (input.cursor) {
     return planTimelineCatchUpAfter({ epoch: input.cursor.epoch, seq: input.cursor.endSeq });
   }
@@ -66,7 +66,7 @@ export function planTimelineCatchUpAfter(cursor: TimelineSyncCursor) {
     direction: "after",
     cursor,
     limit: TIMELINE_FETCH_PAGE_SIZE,
-    projection: "canonical",
+    projection: "projected",
   } as const;
 }
 
@@ -74,7 +74,7 @@ export function planTimelineTailFetch() {
   return {
     direction: "tail",
     limit: TIMELINE_FETCH_PAGE_SIZE,
-    projection: "canonical",
+    projection: "projected",
   } as const;
 }
 
@@ -83,7 +83,7 @@ export function planTimelineOlderFetch(cursor: TimelineSyncCursor) {
     direction: "before",
     cursor,
     limit: TIMELINE_FETCH_PAGE_SIZE,
-    projection: "canonical",
+    projection: "projected",
   } as const;
 }
 
@@ -92,7 +92,7 @@ export function planTimelineCatchUpFollowUp(input: {
   hasNewer: boolean;
   endCursor: TimelineSyncCursor | null;
   error: string | null;
-}): CanonicalTimelineAfterFetchPlan | null {
+}): ProjectedTimelineAfterFetchPlan | null {
   if (input.error || input.direction !== "after" || !input.hasNewer || !input.endCursor) {
     return null;
   }

packages/server/src/server/agent/timeline-projection.test.ts

@@ -3,6 +3,7 @@ import { describe, expect, test } from "vitest";
 import type { AgentTimelineRow } from "./agent-manager.js";
 import {
   projectTimelineRows,
+  selectProjectedTimelinePage,
   selectTimelineWindowByProjectedLimit,
 } from "./timeline-projection.js";
 
@@ -436,58 +437,178 @@ describe("selectTimelineWindowByProjectedLimit", () => {
     });
   });
 
-  test("can enforce a hard projected limit when tool lifecycle collapsing is disabled", () => {
+  test("tail limit treats a repeated running tool call as one projected item", () => {
     const rows: AgentTimelineRow[] = [
-      {
-        seq: 1,
-        timestamp: "2026-02-13T00:00:00.000Z",
+      ...Array.from({ length: 6 }, (_, index) => ({
+        seq: index + 1,
+        timestamp: `2026-02-13T00:00:00.00${index}Z`,
+        item: { type: "assistant_message" as const, text: `old ${index}` },
+      })),
+      ...Array.from({ length: 20 }, (_, index) => ({
+        seq: index + 7,
+        timestamp: `2026-02-13T00:00:01.0${index}Z`,
         item: {
-          type: "tool_call",
+          type: "tool_call" as const,
           callId: "call_1",
           name: "shell",
-          status: "running",
+          status: "running" as const,
           error: null,
           detail: {
-            type: "unknown",
-            input: { cmd: "pwd" },
-            output: null,
+            type: "unknown" as const,
+            input: { cmd: "sleep 10" },
+            output: { progress: index },
           },
         },
-      },
-      {
-        seq: 2,
-        timestamp: "2026-02-13T00:00:00.100Z",
-        item: { type: "assistant_message", text: "work" },
-      },
-      {
-        seq: 3,
-        timestamp: "2026-02-13T00:00:00.200Z",
-        item: {
-          type: "tool_call",
-          callId: "call_1",
-          name: "shell",
-          status: "completed",
-          error: null,
-          detail: {
-            type: "unknown",
-            input: { cmd: "pwd" },
-            output: { stdout: "/tmp" },
-          },
-        },
-      },
+      })),
     ];
 
     const selected = selectTimelineWindowByProjectedLimit({
       rows,
       direction: "tail",
-      limit: 1,
-      collapseToolLifecycle: false,
+      limit: 100,
     });
 
-    expect(selected.minSeq).toBe(3);
-    expect(selected.maxSeq).toBe(3);
-    expect(selected.selectedRows.map((row) => row.seq)).toEqual([3]);
-    expect(selected.projectedEntries).toHaveLength(1);
-    expect(selected.projectedEntries[0]?.item.type).toBe("tool_call");
+    const tools = selected.projectedEntries.filter((entry) => entry.item.type === "tool_call");
+    expect(tools).toHaveLength(1);
+    expect(tools[0]?.collapsed).toContain("tool_lifecycle");
+    expect(selected.projectedEntries).toHaveLength(2);
+  });
+});
+
+describe("selectProjectedTimelinePage", () => {
+  function toolRow(seq: number, status: "running" | "completed"): AgentTimelineRow {
+    return {
+      seq,
+      timestamp: new Date(1000 + seq).toISOString(),
+      item: {
+        type: "tool_call",
+        callId: "call_1",
+        name: "shell",
+        status,
+        error: null,
+        detail: {
+          type: "unknown",
+          input: { cmd: "sleep 10" },
+          output: status === "completed" ? { stdout: "done" } : null,
+        },
+      },
+    };
+  }
+
+  test("tail page returns full projected items instead of tool lifecycle deltas", () => {
+    const rows: AgentTimelineRow[] = [
+      { seq: 1, timestamp: "2026-02-13T00:00:00.000Z", item: { type: "user_message", text: "go" } },
+      ...Array.from({ length: 120 }, (_, index) => toolRow(index + 2, "running")),
+    ];
+
+    const page = selectProjectedTimelinePage({ rows, direction: "tail", limit: 100 });
+
+    expect(page.entries.map((entry) => entry.item.type)).toEqual(["user_message", "tool_call"]);
+    expect(page.entries[1]?.collapsed).toContain("tool_lifecycle");
+    expect(page.entries[1]?.sourceSeqRanges).toEqual([{ startSeq: 2, endSeq: 121 }]);
+    expect(page.startSeq).toBe(1);
+    expect(page.endSeq).toBe(121);
+    expect(page.hasNewer).toBe(false);
+  });
+
+  test("after page includes a full projected tool item when only its update is new", () => {
+    const rows: AgentTimelineRow[] = [
+      toolRow(10, "running"),
+      {
+        seq: 11,
+        timestamp: "2026-02-13T00:00:00.011Z",
+        item: { type: "assistant_message", text: "working" },
+      },
+      toolRow(250, "completed"),
+    ];
+
+    const page = selectProjectedTimelinePage({
+      rows,
+      direction: "after",
+      cursorSeq: 249,
+      limit: 100,
+    });
+
+    expect(page.entries).toHaveLength(1);
+    expect(page.entries[0]?.item.type).toBe("tool_call");
+    expect(page.entries[0]?.seqStart).toBe(10);
+    expect(page.entries[0]?.seqEnd).toBe(250);
+    expect(page.entries[0]?.sourceSeqRanges).toEqual([
+      { startSeq: 10, endSeq: 10 },
+      { startSeq: 250, endSeq: 250 },
+    ]);
+    expect(page.startSeq).toBe(250);
+    expect(page.endSeq).toBe(250);
+  });
+
+  test("after page cursor advances only through contiguously covered seqs", () => {
+    const rows: AgentTimelineRow[] = [
+      toolRow(1, "running"),
+      ...Array.from({ length: 498 }, (_, index) => ({
+        seq: index + 2,
+        timestamp: new Date(2000 + index).toISOString(),
+        item: { type: "user_message" as const, text: `middle ${index + 2}` },
+      })),
+      toolRow(500, "completed"),
+      ...Array.from({ length: 101 }, (_, index) => ({
+        seq: index + 501,
+        timestamp: new Date(3000 + index).toISOString(),
+        item: { type: "user_message" as const, text: `later ${index + 501}` },
+      })),
+    ];
+
+    const page = selectProjectedTimelinePage({
+      rows,
+      direction: "after",
+      cursorSeq: 0,
+      limit: 100,
+    });
+
+    expect(page.entries[0]?.item.type).toBe("tool_call");
+    expect(
+      page.entries.some((entry) => entry.item.type === "user_message" && entry.seqStart === 101),
+    ).toBe(false);
+    expect(page.endSeq).toBe(100);
+    expect(page.hasNewer).toBe(true);
+  });
+
+  test("before page includes a wide tool whose earlier source range is before the cursor", () => {
+    const rows: AgentTimelineRow[] = [
+      toolRow(1, "running"),
+      ...Array.from({ length: 498 }, (_, index) => ({
+        seq: index + 2,
+        timestamp: new Date(2000 + index).toISOString(),
+        item: { type: "user_message" as const, text: `middle ${index + 2}` },
+      })),
+      toolRow(500, "completed"),
+    ];
+
+    const page = selectProjectedTimelinePage({
+      rows,
+      direction: "before",
+      cursorSeq: 500,
+      limit: 100,
+    });
+
+    expect(page.entries.some((entry) => entry.item.type === "tool_call")).toBe(true);
+    expect(page.endSeq).toBeLessThan(500);
+    expect(page.hasOlder).toBe(true);
+  });
+
+  test("tail page includes a wide tool when its completion is the newest seq", () => {
+    const rows: AgentTimelineRow[] = [
+      toolRow(1, "running"),
+      ...Array.from({ length: 499 }, (_, index) => ({
+        seq: index + 2,
+        timestamp: new Date(2000 + index).toISOString(),
+        item: { type: "user_message" as const, text: `middle ${index + 2}` },
+      })),
+      toolRow(501, "completed"),
+    ];
+
+    const page = selectProjectedTimelinePage({ rows, direction: "tail", limit: 100 });
+
+    expect(page.entries.some((entry) => entry.item.type === "tool_call")).toBe(true);
+    expect(page.endSeq).toBe(501);
   });
 });

packages/server/src/server/agent/timeline-projection.ts

@@ -28,6 +28,14 @@ interface ProjectedWindowSelection {
   maxSeq: number | null;
 }
 
+export interface ProjectedTimelinePageSelection {
+  entries: TimelineProjectionEntry[];
+  startSeq: number | null;
+  endSeq: number | null;
+  hasOlder: boolean;
+  hasNewer: boolean;
+}
+
 function appendSeqToRanges(ranges: TimelineSeqRange[], seq: number): TimelineSeqRange[] {
   if (ranges.length === 0) {
     return [{ startSeq: seq, endSeq: seq }];
@@ -266,15 +274,11 @@ export function selectTimelineWindowByProjectedLimit(input: {
   rows: readonly AgentTimelineRow[];
   direction: TimelineLimitDirection;
   limit: number;
-  collapseToolLifecycle?: boolean;
 }): ProjectedWindowSelection {
   const { rows, direction } = input;
   const limit = Math.max(0, Math.floor(input.limit));
-  const collapseTools = input.collapseToolLifecycle ?? true;
   const canonical = makeCanonicalEntries(rows);
-  const projectedAll = mergeReasoningChunks(
-    mergeAssistantChunks(collapseTools ? collapseToolLifecycle(canonical) : canonical),
-  );
+  const projectedAll = mergeReasoningChunks(mergeAssistantChunks(collapseToolLifecycle(canonical)));
 
   if (projectedAll.length === 0) {
     return {
@@ -320,27 +324,25 @@ export function selectTimelineWindowByProjectedLimit(input: {
   let { minSeq, maxSeq } = computeWindowBounds(projectedEntries);
   let expandedEntries = projectedEntries;
 
-  if (collapseTools) {
-    // Expand to include any projected entries that overlap the selected
-    // canonical range. Tool lifecycle collapse can produce non-monotonic
-    // seqEnd values, which would otherwise create cursor gaps.
-    for (let iteration = 0; iteration < projectedAll.length + 1; iteration += 1) {
-      const overlapping = projectedAll.filter(
-        (entry) => entry.seqStart <= maxSeq && entry.seqEnd >= minSeq,
-      );
-      const nextBounds = computeWindowBounds(overlapping);
-      if (
-        overlapping.length === expandedEntries.length &&
-        nextBounds.minSeq === minSeq &&
-        nextBounds.maxSeq === maxSeq
-      ) {
-        expandedEntries = overlapping;
-        break;
-      }
+  // Expand to include any projected entries that overlap the selected canonical
+  // range. Tool lifecycle collapse can produce non-monotonic seqEnd values,
+  // which would otherwise create cursor gaps.
+  for (let iteration = 0; iteration < projectedAll.length + 1; iteration += 1) {
+    const overlapping = projectedAll.filter(
+      (entry) => entry.seqStart <= maxSeq && entry.seqEnd >= minSeq,
+    );
+    const nextBounds = computeWindowBounds(overlapping);
+    if (
+      overlapping.length === expandedEntries.length &&
+      nextBounds.minSeq === minSeq &&
+      nextBounds.maxSeq === maxSeq
+    ) {
       expandedEntries = overlapping;
-      minSeq = nextBounds.minSeq;
-      maxSeq = nextBounds.maxSeq;
+      break;
     }
+    expandedEntries = overlapping;
+    minSeq = nextBounds.minSeq;
+    maxSeq = nextBounds.maxSeq;
   }
 
   const selectedRows = rows.filter((row) => row.seq >= minSeq && row.seq <= maxSeq);
@@ -353,6 +355,94 @@ export function selectTimelineWindowByProjectedLimit(input: {
   };
 }
 
+function getTimelineBounds(
+  rows: readonly AgentTimelineRow[],
+): { minSeq: number; maxSeq: number } | null {
+  const first = rows[0];
+  const last = rows[rows.length - 1];
+  if (!first || !last) {
+    return null;
+  }
+  return { minSeq: first.seq, maxSeq: last.seq };
+}
+
+function selectEntriesOverlappingSeqRange(input: {
+  entries: readonly TimelineProjectionEntry[];
+  startSeq: number;
+  endSeq: number;
+}): TimelineProjectionEntry[] {
+  return input.entries.filter(
+    (entry) => entry.seqStart <= input.endSeq && entry.seqEnd >= input.startSeq,
+  );
+}
+
+export function selectProjectedTimelinePage(input: {
+  rows: readonly AgentTimelineRow[];
+  bounds?: { minSeq: number; maxSeq: number };
+  direction: TimelineLimitDirection;
+  cursorSeq?: number;
+  limit?: number;
+}): ProjectedTimelinePageSelection {
+  const limit = input.limit === undefined ? 0 : Math.max(0, Math.floor(input.limit));
+  const bounds = input.bounds ?? getTimelineBounds(input.rows);
+  const projectedAll = projectTimelineRows({ rows: input.rows, mode: "projected" });
+  if (projectedAll.length === 0 || !bounds) {
+    return {
+      entries: [],
+      startSeq: null,
+      endSeq: null,
+      hasOlder: false,
+      hasNewer: false,
+    };
+  }
+
+  if (input.direction === "tail") {
+    const selected = selectTimelineWindowByProjectedLimit({
+      rows: input.rows,
+      direction: "tail",
+      limit,
+    });
+    return {
+      entries: selected.projectedEntries,
+      startSeq: selected.minSeq,
+      endSeq: selected.maxSeq,
+      hasOlder: selected.minSeq !== null && selected.minSeq > bounds.minSeq,
+      hasNewer: false,
+    };
+  }
+
+  let startSeq: number;
+  let endSeq: number;
+  if (input.direction === "after") {
+    const cursorSeq = input.cursorSeq ?? bounds.minSeq - 1;
+    startSeq = Math.max(bounds.minSeq, cursorSeq + 1);
+    endSeq = limit === 0 ? bounds.maxSeq : Math.min(bounds.maxSeq, cursorSeq + limit);
+  } else {
+    const cursorSeq = input.cursorSeq ?? bounds.maxSeq + 1;
+    endSeq = Math.min(bounds.maxSeq, cursorSeq - 1);
+    startSeq = limit === 0 ? bounds.minSeq : Math.max(bounds.minSeq, cursorSeq - limit);
+  }
+
+  if (startSeq > endSeq) {
+    return {
+      entries: [],
+      startSeq: null,
+      endSeq: null,
+      hasOlder: startSeq > bounds.minSeq,
+      hasNewer: endSeq < bounds.maxSeq,
+    };
+  }
+
+  const entries = selectEntriesOverlappingSeqRange({ entries: projectedAll, startSeq, endSeq });
+  return {
+    entries,
+    startSeq,
+    endSeq,
+    hasOlder: startSeq > bounds.minSeq,
+    hasNewer: endSeq < bounds.maxSeq,
+  };
+}
+
 /**
  * Apply a projected-count limit to a flat AgentTimelineItem[] without seq metadata.
  * Used by callers that only have items in hand (e.g. MCP tools reading

packages/server/src/server/daemon-e2e/timeline-window.e2e.test.ts

@@ -1,4 +1,4 @@
-import { describe, test, expect, beforeEach, afterEach } from "vitest";
+import { describe, test, expect, beforeEach, afterEach, vi } from "vitest";
 import { mkdtempSync, rmSync } from "node:fs";
 import { tmpdir } from "node:os";
 import path from "node:path";
@@ -17,6 +17,7 @@ describe("daemon E2E - timeline window", () => {
   });
 
   afterEach(async () => {
+    vi.restoreAllMocks();
     await ctx.cleanup();
   }, 60_000);
 
@@ -66,6 +67,10 @@ describe("daemon E2E - timeline window", () => {
       expect((await ctx.client.waitForFinish(agent.id, 5_000)).status).toBe("idle");
 
       const expected = "SECOND";
+      await ctx.daemon.daemon.agentManager.appendTimelineItem(agent.id, {
+        type: "user_message",
+        text: "next",
+      });
       await ctx.client.sendMessage(agent.id, `Respond with exactly: ${expected}`);
       expect((await ctx.client.waitForFinish(agent.id, 5_000)).status).toBe("idle");
 
@@ -86,4 +91,271 @@ describe("daemon E2E - timeline window", () => {
       rmSync(cwd, { recursive: true, force: true });
     }
   }, 30_000);
+
+  test("timeline fetch returns one projected in-progress tool call instead of lifecycle deltas", async () => {
+    const cwd = tmpCwd();
+    try {
+      const agent = await ctx.client.createAgent({
+        provider: "codex",
+        cwd,
+        title: "Timeline Tool Projection Test",
+        modeId: "full-access",
+      });
+
+      await ctx.daemon.daemon.agentManager.appendTimelineItem(agent.id, {
+        type: "user_message",
+        text: "run the tool",
+      });
+      for (let index = 0; index < 120; index += 1) {
+        await ctx.daemon.daemon.agentManager.appendTimelineItem(agent.id, {
+          type: "tool_call",
+          callId: "call_1",
+          name: "shell",
+          status: "running",
+          error: null,
+          detail: {
+            type: "unknown",
+            input: { cmd: "sleep 10" },
+            output: { progress: index },
+          },
+        });
+      }
+
+      const timeline = await ctx.client.fetchAgentTimeline(agent.id, {
+        direction: "tail",
+        limit: 100,
+        projection: "canonical",
+      });
+
+      const toolEntries = timeline.entries.filter((entry) => entry.item.type === "tool_call");
+      expect(timeline.projection).toBe("projected");
+      expect(timeline.entries.map((entry) => entry.item.type)).toEqual([
+        "user_message",
+        "tool_call",
+      ]);
+      expect(toolEntries).toHaveLength(1);
+      expect(toolEntries[0]?.collapsed).toContain("tool_lifecycle");
+      expect(toolEntries[0]?.sourceSeqRanges).toEqual([{ startSeq: 2, endSeq: 121 }]);
+      expect(timeline.endCursor?.seq).toBe(121);
+    } finally {
+      rmSync(cwd, { recursive: true, force: true });
+    }
+  });
+
+  test("after fetch returns the full projected tool item for a new lifecycle update", async () => {
+    const cwd = tmpCwd();
+    try {
+      const agent = await ctx.client.createAgent({
+        provider: "codex",
+        cwd,
+        title: "Timeline Tool Catch-up Test",
+        modeId: "full-access",
+      });
+
+      await ctx.daemon.daemon.agentManager.appendTimelineItem(agent.id, {
+        type: "tool_call",
+        callId: "call_1",
+        name: "shell",
+        status: "running",
+        error: null,
+        detail: {
+          type: "unknown",
+          input: { cmd: "sleep 10" },
+          output: null,
+        },
+      });
+      for (let seq = 2; seq <= 249; seq += 1) {
+        await ctx.daemon.daemon.agentManager.appendTimelineItem(agent.id, {
+          type: "assistant_message",
+          text: `background ${seq}`,
+        });
+      }
+      await ctx.daemon.daemon.agentManager.appendTimelineItem(agent.id, {
+        type: "tool_call",
+        callId: "call_1",
+        name: "shell",
+        status: "completed",
+        error: null,
+        detail: {
+          type: "unknown",
+          input: { cmd: "sleep 10" },
+          output: { stdout: "done" },
+        },
+      });
+
+      const baseline = await ctx.client.fetchAgentTimeline(agent.id, {
+        direction: "tail",
+        limit: 0,
+      });
+      const timeline = await ctx.client.fetchAgentTimeline(agent.id, {
+        direction: "after",
+        cursor: { epoch: baseline.epoch, seq: 249 },
+        limit: 100,
+        projection: "canonical",
+      });
+
+      expect(timeline.entries).toHaveLength(1);
+      expect(timeline.startCursor?.seq).toBe(250);
+      expect(timeline.endCursor?.seq).toBe(250);
+      expect(timeline.entries[0]?.seqStart).toBe(1);
+      expect(timeline.entries[0]?.seqEnd).toBe(250);
+      expect(timeline.entries[0]?.sourceSeqRanges).toEqual([
+        { startSeq: 1, endSeq: 1 },
+        { startSeq: 250, endSeq: 250 },
+      ]);
+      expect(timeline.entries[0]?.item.type).toBe("tool_call");
+    } finally {
+      rmSync(cwd, { recursive: true, force: true });
+    }
+  });
+
+  test("reset timeline fetch reports older history when the reset slice starts after window min", async () => {
+    const cwd = tmpCwd();
+    try {
+      const agent = await ctx.client.createAgent({
+        provider: "codex",
+        cwd,
+        title: "Timeline Reset HasOlder Test",
+        modeId: "full-access",
+      });
+
+      for (let seq = 1; seq <= 600; seq += 1) {
+        await ctx.daemon.daemon.agentManager.appendTimelineItem(agent.id, {
+          type: "user_message",
+          text: `row ${seq}`,
+        });
+      }
+
+      const timeline = await ctx.client.fetchAgentTimeline(agent.id, {
+        direction: "tail",
+        cursor: { epoch: "stale-epoch", seq: 600 },
+        limit: 200,
+      });
+
+      expect(timeline.reset).toBe(true);
+      expect(timeline.staleCursor).toBe(true);
+      expect(timeline.startCursor?.seq).toBeGreaterThan(timeline.window.minSeq);
+      expect(timeline.hasOlder).toBe(true);
+    } finally {
+      rmSync(cwd, { recursive: true, force: true });
+    }
+  });
+
+  test("tail fetch does not re-fetch full plain chat history", async () => {
+    const cwd = tmpCwd();
+    try {
+      const agent = await ctx.client.createAgent({
+        provider: "codex",
+        cwd,
+        title: "Timeline Tail Bounded Fetch Test",
+        modeId: "full-access",
+      });
+      for (let seq = 1; seq <= 600; seq += 1) {
+        await ctx.daemon.daemon.agentManager.appendTimelineItem(agent.id, {
+          type: "user_message",
+          text: `row ${seq}`,
+        });
+      }
+
+      const fetchSpy = vi.spyOn(ctx.daemon.daemon.agentManager, "fetchTimeline");
+      const timeline = await ctx.client.fetchAgentTimeline(agent.id, {
+        direction: "tail",
+        limit: 100,
+      });
+
+      expect(timeline.entries).toHaveLength(100);
+      expect(timeline.startCursor?.seq).toBe(501);
+      expect(timeline.endCursor?.seq).toBe(600);
+      expect(timeline.hasOlder).toBe(true);
+      expect(
+        fetchSpy.mock.calls.some(
+          ([, options]) => options?.direction === "tail" && options.limit === 0,
+        ),
+      ).toBe(false);
+    } finally {
+      rmSync(cwd, { recursive: true, force: true });
+    }
+  });
+
+  test("after fetch does not re-fetch full plain chat history", async () => {
+    const cwd = tmpCwd();
+    try {
+      const agent = await ctx.client.createAgent({
+        provider: "codex",
+        cwd,
+        title: "Timeline After Bounded Fetch Test",
+        modeId: "full-access",
+      });
+      for (let seq = 1; seq <= 600; seq += 1) {
+        await ctx.daemon.daemon.agentManager.appendTimelineItem(agent.id, {
+          type: "user_message",
+          text: `row ${seq}`,
+        });
+      }
+      const epoch = ctx.daemon.daemon.agentManager.fetchTimeline(agent.id, {
+        direction: "tail",
+        limit: 1,
+      }).epoch;
+
+      const fetchSpy = vi.spyOn(ctx.daemon.daemon.agentManager, "fetchTimeline");
+      const timeline = await ctx.client.fetchAgentTimeline(agent.id, {
+        direction: "after",
+        cursor: { epoch, seq: 300 },
+        limit: 100,
+      });
+
+      expect(timeline.entries).toHaveLength(100);
+      expect(timeline.startCursor?.seq).toBe(301);
+      expect(timeline.endCursor?.seq).toBe(400);
+      expect(timeline.hasNewer).toBe(true);
+      expect(
+        fetchSpy.mock.calls.some(
+          ([, options]) => options?.direction === "tail" && options.limit === 0,
+        ),
+      ).toBe(false);
+    } finally {
+      rmSync(cwd, { recursive: true, force: true });
+    }
+  });
+
+  test("before fetch does not re-fetch full plain chat history", async () => {
+    const cwd = tmpCwd();
+    try {
+      const agent = await ctx.client.createAgent({
+        provider: "codex",
+        cwd,
+        title: "Timeline Before Bounded Fetch Test",
+        modeId: "full-access",
+      });
+      for (let seq = 1; seq <= 600; seq += 1) {
+        await ctx.daemon.daemon.agentManager.appendTimelineItem(agent.id, {
+          type: "user_message",
+          text: `row ${seq}`,
+        });
+      }
+      const epoch = ctx.daemon.daemon.agentManager.fetchTimeline(agent.id, {
+        direction: "tail",
+        limit: 1,
+      }).epoch;
+
+      const fetchSpy = vi.spyOn(ctx.daemon.daemon.agentManager, "fetchTimeline");
+      const timeline = await ctx.client.fetchAgentTimeline(agent.id, {
+        direction: "before",
+        cursor: { epoch, seq: 501 },
+        limit: 100,
+      });
+
+      expect(timeline.entries).toHaveLength(100);
+      expect(timeline.startCursor?.seq).toBe(401);
+      expect(timeline.endCursor?.seq).toBe(500);
+      expect(timeline.hasOlder).toBe(true);
+      expect(
+        fetchSpy.mock.calls.some(
+          ([, options]) => options?.direction === "tail" && options.limit === 0,
+        ),
+      ).toBe(false);
+    } finally {
+      rmSync(cwd, { recursive: true, force: true });
+    }
+  });
 });

packages/server/src/server/session.ts

@@ -99,6 +99,7 @@ import type {
   AgentManagerEvent,
   AgentTimelineCursor,
   AgentTimelineFetchDirection,
+  AgentTimelineFetchResult,
   ManagedAgent,
 } from "./agent/agent-manager.js";
 import { createAgentCommand } from "./agent/create-agent/create.js";
@@ -120,8 +121,7 @@ import {
   emitLiveTimelineItemIfAgentKnown,
 } from "./agent/timeline-append.js";
 import {
-  projectTimelineRows,
-  selectTimelineWindowByProjectedLimit,
+  selectProjectedTimelinePage,
   type TimelineProjectionMode,
 } from "./agent/timeline-projection.js";
 import {
@@ -7415,84 +7415,33 @@ export class Session {
     });
   }
 
-  private loadProjectedTimelineWindow(params: {
-    agentId: string;
-    direction: AgentTimelineFetchDirection;
-    cursor: AgentTimelineCursor | undefined;
-    requestedLimit: number;
-    timeline: ReturnType<AgentManager["fetchTimeline"]>;
-  }): {
-    timeline: ReturnType<AgentManager["fetchTimeline"]>;
-    selectedRows: ReturnType<typeof selectTimelineWindowByProjectedLimit>["selectedRows"];
-    minSeq: number | null;
-    maxSeq: number | null;
-  } {
-    const { agentId, direction, cursor, requestedLimit } = params;
-    let timeline = params.timeline;
-    const projectedLimit = Math.max(1, Math.floor(requestedLimit));
-    let fetchLimit = projectedLimit;
-    let projectedWindow = selectTimelineWindowByProjectedLimit({
-      rows: timeline.rows,
-      direction,
-      limit: projectedLimit,
-      collapseToolLifecycle: false,
-    });
-
-    while (timeline.hasOlder) {
-      const needsMoreProjectedEntries = projectedWindow.projectedEntries.length < projectedLimit;
-      const firstLoadedRow = timeline.rows[0];
-      const firstSelectedRow = projectedWindow.selectedRows[0];
-      const startsAtLoadedBoundary =
-        firstLoadedRow != null &&
-        firstSelectedRow != null &&
-        firstSelectedRow.seq === firstLoadedRow.seq;
-      const boundaryIsAssistantChunk =
-        startsAtLoadedBoundary && firstLoadedRow.item.type === "assistant_message";
-
-      if (!needsMoreProjectedEntries && !boundaryIsAssistantChunk) {
-        break;
-      }
-
-      const maxRows = Math.max(0, timeline.window.maxSeq - timeline.window.minSeq + 1);
-      const nextFetchLimit = Math.min(maxRows, fetchLimit * 2);
-      if (nextFetchLimit <= fetchLimit) {
-        break;
-      }
-
-      fetchLimit = nextFetchLimit;
-      timeline = this.agentManager.fetchTimeline(agentId, {
-        direction,
-        cursor,
-        limit: fetchLimit,
-      });
-      projectedWindow = selectTimelineWindowByProjectedLimit({
-        rows: timeline.rows,
-        direction,
-        limit: projectedLimit,
-        collapseToolLifecycle: false,
-      });
+  private shouldUseFullTimelineForProjectedPage(input: {
+    timeline: AgentTimelineFetchResult;
+  }): boolean {
+    const { timeline } = input;
+    if (timeline.reset || timeline.rows.length === 0 || !timeline.hasOlder) {
+      return false;
     }
 
-    return {
-      timeline,
-      selectedRows: projectedWindow.selectedRows,
-      minSeq: projectedWindow.minSeq,
-      maxSeq: projectedWindow.maxSeq,
-    };
+    const firstRow = timeline.rows[0];
+    if (
+      firstRow?.item.type === "assistant_message" ||
+      firstRow?.item.type === "reasoning" ||
+      firstRow?.item.type === "tool_call"
+    ) {
+      return true;
+    }
+
+    return timeline.rows.some((row) => row.item.type === "tool_call");
   }
 
   private async handleFetchAgentTimelineRequest(
     msg: Extract<SessionInboundMessage, { type: "fetch_agent_timeline_request" }>,
   ): Promise<void> {
     const direction: AgentTimelineFetchDirection = msg.direction ?? (msg.cursor ? "after" : "tail");
-    const projection: TimelineProjectionMode = msg.projection ?? "projected";
+    const projection: TimelineProjectionMode = "projected";
     const requestedLimit = msg.limit;
-    const limit = requestedLimit ?? (direction === "after" ? 0 : undefined);
-    const shouldLimitByProjectedWindow =
-      projection === "canonical" &&
-      direction === "tail" &&
-      typeof requestedLimit === "number" &&
-      requestedLimit > 0;
+    const pageLimit = requestedLimit ?? (direction === "after" ? 0 : 200);
     const cursor: AgentTimelineCursor | undefined = msg.cursor
       ? {
           epoch: msg.cursor.epoch,
@@ -7508,43 +7457,29 @@ export class Session {
       });
       const agentPayload = await this.buildAgentPayload(snapshot);
 
-      let timeline = this.agentManager.fetchTimeline(msg.agentId, {
+      const controlTimeline = this.agentManager.fetchTimeline(msg.agentId, {
         direction,
         cursor,
-        limit:
-          shouldLimitByProjectedWindow && typeof requestedLimit === "number"
-            ? Math.max(1, Math.floor(requestedLimit))
-            : limit,
+        limit: pageLimit,
       });
-      let hasOlder = timeline.hasOlder;
-      let hasNewer = timeline.hasNewer;
-      let startCursor: { epoch: string; seq: number } | null = null;
-      let endCursor: { epoch: string; seq: number } | null = null;
-      let entries: ReturnType<typeof projectTimelineRows>;
-
-      if (shouldLimitByProjectedWindow) {
-        const projectedResult = this.loadProjectedTimelineWindow({
-          agentId: msg.agentId,
-          direction,
-          cursor,
-          requestedLimit,
-          timeline,
-        });
-        timeline = projectedResult.timeline;
-        entries = projectTimelineRows({ rows: projectedResult.selectedRows, mode: projection });
-        if (projectedResult.minSeq !== null && projectedResult.maxSeq !== null) {
-          startCursor = { epoch: timeline.epoch, seq: projectedResult.minSeq };
-          endCursor = { epoch: timeline.epoch, seq: projectedResult.maxSeq };
-          hasOlder = projectedResult.minSeq > timeline.window.minSeq;
-          hasNewer = false;
-        }
-      } else {
-        const firstRow = timeline.rows[0];
-        const lastRow = timeline.rows[timeline.rows.length - 1];
-        startCursor = firstRow ? { epoch: timeline.epoch, seq: firstRow.seq } : null;
-        endCursor = lastRow ? { epoch: timeline.epoch, seq: lastRow.seq } : null;
-        entries = projectTimelineRows({ rows: timeline.rows, mode: projection });
-      }
+      const timeline = this.shouldUseFullTimelineForProjectedPage({
+        timeline: controlTimeline,
+      })
+        ? this.agentManager.fetchTimeline(msg.agentId, { direction: "tail", limit: 0 })
+        : controlTimeline;
+      const projectedPage = selectProjectedTimelinePage({
+        rows: timeline.rows,
+        bounds: timeline.window,
+        direction: controlTimeline.reset ? "tail" : direction,
+        ...(cursor ? { cursorSeq: cursor.seq } : {}),
+        limit: pageLimit,
+      });
+      const startCursor =
+        projectedPage.startSeq !== null
+          ? { epoch: timeline.epoch, seq: projectedPage.startSeq }
+          : null;
+      const endCursor =
+        projectedPage.endSeq !== null ? { epoch: timeline.epoch, seq: projectedPage.endSeq } : null;
 
       this.emit({
         type: "fetch_agent_timeline_response",
@@ -7555,15 +7490,17 @@ export class Session {
           direction,
           projection,
           epoch: timeline.epoch,
-          reset: timeline.reset,
-          staleCursor: timeline.staleCursor,
-          gap: timeline.gap,
+          reset: controlTimeline.reset,
+          staleCursor: controlTimeline.staleCursor,
+          gap: controlTimeline.gap,
           window: timeline.window,
           startCursor,
           endCursor,
-          hasOlder,
-          hasNewer,
-          entries: entries.map((entry) => ({
+          hasOlder:
+            projectedPage.hasOlder ||
+            (projectedPage.startSeq !== null && projectedPage.startSeq > timeline.window.minSeq),
+          hasNewer: projectedPage.hasNewer,
+          entries: projectedPage.entries.map((entry) => ({
             provider: snapshot.provider,
             item: entry.item,
             timestamp: entry.timestamp,