test(server): keep timeline page oracle outside production builds

Keep page selection and source coverage indexes with the retained projection so bounded fetches and last-message lookups do not copy or reproject history. Omitted after limits use the existing 200-item store default; explicit zero remains unlimited for released CLI clients.

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

@@ -1,4 +1,6 @@
 import { describe, expect, it } from "vitest";
+import { selectReferenceProjectedTimelinePage } from "./test-utils/timeline-page-reference.js";
+import type { AgentTimelineItem } from "./agent-sdk-types.js";
 import { InMemoryAgentTimelineStore } from "./agent-timeline-store.js";
 
 describe("InMemoryAgentTimelineStore", () => {
@@ -177,7 +179,10 @@ describe("projected sequence ownership", () => {
     store.append("a", { type: "assistant_message", text: "Answer" });
     store.append("a", { ...tool, status: "completed" });
     store.initialize("b", { rows: store.getRows("a") });
+    expect(store.getLastItem("b")).toMatchObject({ type: "tool_call", status: "completed" });
+    expect(store.getLastAssistantMessage("b")).toBe("Answer");
     expect(store.append("b", { type: "user_message", text: "next" }).seq).toBe(4);
+    expect(store.getLastItem("b")).toEqual({ type: "user_message", text: "next" });
     expect(store.fetch("b").rows.map((row) => row.seqStart)).toEqual([1, 2, 4]);
   });
   it("returns the last projected assistant message without joining different messages", () => {
@@ -211,3 +216,151 @@ it("includes transitive tool updates in a contiguous projected tail", () => {
   expect(tail.rows.map((row) => row.seqStart)).toEqual([1, 2, 3, 5]);
   expect(tail).toMatchObject({ startSeq: 1, endSeq: 6, hasOlder: false });
 });
+
+it("serves tail 200 from 100,000 retained rows without stalling the loop", async () => {
+  const store = new InMemoryAgentTimelineStore();
+  store.initialize("large");
+  for (let index = 0; index < 100_000; index++) {
+    store.append("large", { type: "user_message", text: String(index) });
+  }
+  // Generation and its GC are outside the measured request window.
+  await new Promise<void>((resolve) => setImmediate(resolve));
+  const started = performance.now();
+  const probe = new Promise<number>((resolve) =>
+    setImmediate(() => resolve(performance.now() - started)),
+  );
+  let page = store.fetch("large", { limit: 200 });
+  for (let repeat = 1; repeat < 8; repeat++) page = store.fetch("large", { limit: 200 });
+  const duration = performance.now() - started;
+  const loopGap = await probe;
+  console.info({ duration, loopGap });
+  expect(page.rows).toHaveLength(200);
+  expect(page.startSeq).toBe(99_801);
+  expect(page.endSeq).toBe(100_000);
+  // CI runners can pause for scheduling/GC; the local per-request 2 ms gate
+  // is measured separately. Eight requests amplify the old full-history work.
+  expect(duration).toBeLessThan(50);
+  expect(loopGap).toBeLessThan(50);
+});
+
+it("matches the previous reprojecting selector on seeded randomized timelines", () => {
+  let seed = 0x76aabbcc;
+  const random = (bound: number) => {
+    seed = (Math.imul(seed, 1664525) + 1013904223) >>> 0;
+    return Math.floor((seed / 0x1_0000_0000) * bound);
+  };
+  for (let scenario = 0; scenario < 100; scenario++) {
+    const store = new InMemoryAgentTimelineStore();
+    store.initialize("a", { epoch: "e" });
+    for (let seq = 1; seq <= 100; seq++) {
+      const identity = String(random(8));
+      const text = String(seq);
+      const items: AgentTimelineItem[] = [
+        { type: "user_message", text },
+        { type: "assistant_message", text },
+        { type: "assistant_message", text, messageId: identity },
+        { type: "reasoning", text },
+        {
+          type: "tool_call",
+          callId: identity,
+          name: "shell",
+          status: "running",
+          error: null,
+          detail: { type: "plain_text", label: text },
+        },
+        {
+          type: "plugin",
+          id: identity,
+          pluginId: "test",
+          kind: "state",
+          version: 1,
+          data: { text },
+        },
+      ];
+      store.append("a", items[random(items.length)], { turnId: String(random(3)) });
+    }
+    // Include rehydration of already-projected rows, with non-monotonic seqEnd.
+    store.initialize("b", { rows: store.getRows("a"), epoch: "e" });
+    for (const agentId of ["a", "b"]) {
+      assertSelectionMatchesReference(store, agentId);
+      store.append(agentId, { type: "assistant_message", text: "later" });
+      assertSelectionMatchesReference(store, agentId);
+    }
+  }
+});
+
+function assertSelectionMatchesReference(store: InMemoryAgentTimelineStore, agentId: string): void {
+  for (const direction of ["tail", "before", "after"] as const) {
+    for (const limit of [0, 1, 7, 200]) {
+      for (const cursorSeq of [0, 1, 25, 50, 99, 100, 150]) {
+        const actual = store.fetch(agentId, {
+          direction,
+          limit,
+          cursor: { epoch: "e", seq: cursorSeq },
+        });
+        const expected = selectReferenceProjectedTimelinePage({
+          rows: store.getRows(agentId),
+          bounds: actual.window,
+          direction,
+          limit,
+          cursorSeq,
+        });
+        expect({
+          ...expected,
+          entries: undefined,
+          rows: expected.entries.map((entry) => Object.assign({ seq: entry.seqEnd }, entry)),
+        }).toEqual({
+          entries: undefined,
+          rows: actual.rows,
+          startSeq: actual.startSeq,
+          endSeq: actual.endSeq,
+          hasOlder: actual.hasOlder,
+          hasNewer: actual.hasNewer,
+        });
+      }
+    }
+  }
+}
+
+it("continues a scroll across appends and lifecycle collapse without losing source coverage", () => {
+  const store = new InMemoryAgentTimelineStore();
+  store.initialize("a", { epoch: "e" });
+  const tool: AgentTimelineItem = {
+    type: "tool_call",
+    callId: "t",
+    name: "shell",
+    status: "running",
+    error: null,
+    detail: { type: "plain_text", label: "work" },
+  };
+  store.append("a", tool);
+  for (let seq = 2; seq <= 5; seq++) store.append("a", { type: "user_message", text: String(seq) });
+  const first = store.fetch("a", { direction: "after", cursor: { epoch: "e", seq: 0 }, limit: 2 });
+  expect(first.endSeq).toBe(2);
+  store.append("a", { ...tool, status: "completed" });
+  store.append("a", { type: "assistant_message", text: "Done" });
+  expect(first.rows[0].item).toMatchObject({ status: "running" });
+  const second = store.fetch("a", {
+    direction: "after",
+    cursor: { epoch: "e", seq: first.endSeq! },
+    limit: 2,
+  });
+  expect(second.rows.map((row) => row.seqStart)).toEqual([3, 4]);
+  expect(second.endSeq).toBe(4);
+  const third = store.fetch("a", {
+    direction: "after",
+    cursor: { epoch: "e", seq: second.endSeq! },
+    limit: 2,
+  });
+  expect(third.rows.map((row) => row.seqStart)).toEqual([1, 5]);
+  expect(third.rows[0].item).toMatchObject({ status: "completed" });
+  expect(third.endSeq).toBe(6);
+  const last = store.fetch("a", {
+    direction: "after",
+    cursor: { epoch: "e", seq: third.endSeq! },
+    limit: 2,
+  });
+  expect(last.rows.map((row) => row.item)).toEqual([{ type: "assistant_message", text: "Done" }]);
+  expect(last.endSeq).toBe(7);
+  expect(last.hasNewer).toBe(false);
+});

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

@@ -1,9 +1,5 @@
 import { randomUUID } from "node:crypto";
-import {
-  TimelineProjection,
-  selectProjectedTimelinePage,
-  type ProjectedTimelineRow,
-} from "./timeline-projection.js";
+import { TimelineProjection, type ProjectedTimelineRow } from "./timeline-projection.js";
 import type { AgentTimelineItem } from "./agent-sdk-types.js";
 import type {
   AgentTimelineFetchOptions,
@@ -43,8 +39,7 @@ export class InMemoryAgentTimelineStore {
       ? options.rows.map(cloneRow)
       : this.buildRowsFromItems(options?.items ?? [], options?.nextSeq ?? 1, timestamp);
     const nextSeq = rows.reduce((next, row) => Math.max(next, row.seq + 1), options?.nextSeq ?? 1);
-    const projection = new TimelineProjection();
-    for (const row of rows) projection.append(row);
+    const projection = new TimelineProjection(rows);
     this.states.set(agentId, {
       epoch: options?.epoch ?? randomUUID(),
       projection,
@@ -97,18 +92,17 @@ export class InMemoryAgentTimelineStore {
     const state = this.requireState(agentId);
     const direction = options?.direction ?? "tail";
     const cursor = options?.cursor;
-    const rows = state.projection.getRows();
+    const hasRows = state.minSeq !== 0;
     const window = { minSeq: state.minSeq, maxSeq: state.nextSeq - 1, nextSeq: state.nextSeq };
     const staleCursor = cursor !== undefined && cursor.epoch !== state.epoch;
     const gap =
       !staleCursor &&
       direction === "after" &&
       cursor !== undefined &&
-      rows.length > 0 &&
+      hasRows &&
       cursor.seq < state.minSeq - 1;
     const reset = staleCursor || gap;
-    const page = selectProjectedTimelinePage({
-      rows,
+    const page = state.projection.selectPage({
       bounds: window,
       direction: reset ? "tail" : direction,
       cursorSeq: cursor?.seq,
@@ -150,14 +144,11 @@ export class InMemoryAgentTimelineStore {
 
   getLastItem(agentId: string): AgentTimelineItem | null {
     const state = this.requireState(agentId);
-    return state.projection.getRows().find((row) => row.seqEnd === state.nextSeq - 1)?.item ?? null;
+    return state.projection.getLastItem(state.nextSeq - 1);
   }
 
   getLastAssistantMessage(agentId: string): string | null {
-    const row = this.requireState(agentId)
-      .projection.getRows()
-      .findLast((candidate) => candidate.item.type === "assistant_message");
-    return row?.item.type === "assistant_message" ? row.item.text : null;
+    return this.requireState(agentId).projection.getLastAssistantMessage();
   }
 
   private requireState(agentId: string): AgentTimelineState {

packages/server/src/server/agent/test-utils/timeline-page-reference.ts

@@ -0,0 +1,249 @@
+// Frozen pre-index page selection: differential oracle for retained projection tests.
+import type { AgentTimelineRow } from "../agent-timeline-store-types.js";
+import {
+  TimelineProjection,
+  projectTimelineRows,
+  type TimelineProjectionEntry,
+  type ProjectedTimelineRow,
+  type TimelineLimitDirection,
+  type ProjectedTimelinePageSelection,
+} from "../timeline-projection.js";
+
+function makeCanonicalEntries(rows: readonly AgentTimelineRow[]): TimelineProjectionEntry[] {
+  return rows.map((row) => {
+    if ("seqStart" in row) return { ...(row as ProjectedTimelineRow) };
+    return {
+      item: row.item,
+      timestamp: row.timestamp,
+      ...(row.turnId ? { turnId: row.turnId } : {}),
+      ...(row.providerMessageId ? { providerMessageId: row.providerMessageId } : {}),
+      seqStart: row.seq,
+      seqEnd: row.seq,
+      sourceSeqRanges: [{ startSeq: row.seq, endSeq: row.seq }],
+      collapsed: [],
+    };
+  });
+}
+
+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;
+  }
+  const entries = makeCanonicalEntries(rows);
+  return {
+    minSeq: entries.reduce((min, e) => Math.min(min, e.seqStart), Infinity),
+    maxSeq: entries.reduce((max, e) => Math.max(max, e.seqEnd), 0),
+  };
+}
+
+function firstSourceSeqInRange(
+  entry: TimelineProjectionEntry,
+  startSeq: number,
+  endSeq: number,
+): number | null {
+  for (const range of entry.sourceSeqRanges) {
+    const firstSeq = Math.max(range.startSeq, startSeq);
+    if (firstSeq <= Math.min(range.endSeq, endSeq)) return firstSeq;
+  }
+  return null;
+}
+
+interface ProjectedEntryCandidate {
+  entry: TimelineProjectionEntry;
+  index: number;
+  firstSourceSeq: number;
+}
+
+function selectProjectedEntriesAfter(input: {
+  entries: readonly TimelineProjectionEntry[];
+  startSeq: number;
+  maxSeq: number;
+  limit: number;
+}): { entries: TimelineProjectionEntry[]; endSeq: number | null } {
+  const eligible = input.entries
+    .map((entry, index) => ({
+      entry,
+      index,
+      firstSourceSeq: firstSourceSeqInRange(entry, input.startSeq, input.maxSeq),
+    }))
+    .filter((candidate): candidate is ProjectedEntryCandidate => candidate.firstSourceSeq !== null)
+    .sort((left, right) => left.firstSourceSeq - right.firstSourceSeq || left.index - right.index);
+  const selected = input.limit === 0 ? eligible : eligible.slice(0, input.limit);
+  const selectedEntries = selected
+    .sort((left, right) => left.index - right.index)
+    .map((candidate) => candidate.entry);
+  if (selectedEntries.length === 0) return { entries: [], endSeq: null };
+
+  const selectedRanges = selectedEntries
+    .flatMap((entry) => entry.sourceSeqRanges)
+    .sort((left, right) => left.startSeq - right.startSeq || left.endSeq - right.endSeq);
+  // Wide projected entries can include future, discontiguous source ranges. The
+  // page cursor advances only through source rows covered without a gap.
+  let endSeq = input.startSeq - 1;
+  for (const range of selectedRanges) {
+    if (range.endSeq <= endSeq) continue;
+    if (range.startSeq > endSeq + 1) break;
+    endSeq = Math.min(range.endSeq, input.maxSeq);
+  }
+
+  return {
+    entries: selectedEntries,
+    endSeq: endSeq >= input.startSeq ? endSeq : null,
+  };
+}
+
+function selectProjectedEntriesBefore(input: {
+  entries: readonly TimelineProjectionEntry[];
+  endSeq: number;
+  limit: number;
+}): { entries: TimelineProjectionEntry[]; startSeq: number | null; hasOlder: boolean } {
+  // Older history follows projected display order. Lifecycle updates can move an
+  // entry's seqEnd without moving its display anchor, so seqStart keeps the full
+  // projected item on exactly one backward page.
+  const eligible = input.entries.filter((entry) => entry.seqStart <= input.endSeq);
+  const selected =
+    input.limit === 0 || input.limit >= eligible.length
+      ? eligible
+      : eligible.slice(eligible.length - input.limit);
+
+  return {
+    entries: selected,
+    startSeq: selected[0]?.seqStart ?? null,
+    hasOlder: selected.length < eligible.length,
+  };
+}
+
+function selectProjectedEntriesTail(
+  projectedAll: TimelineProjectionEntry[],
+  limit: number,
+  bounds: { minSeq: number; maxSeq: number },
+): ProjectedTimelinePageSelection {
+  let start = limit === 0 ? 0 : Math.max(0, projectedAll.length - limit);
+  // Include earlier display anchors with updates in the selected source window,
+  // so a tail certifies contiguous coverage even with interleaved tool updates.
+  for (let i = start - 1; i >= 0; i--) {
+    if (projectedAll[i].seqEnd >= projectedAll[start].seqStart) start = i;
+  }
+  const selected = projectedAll.slice(start);
+  return {
+    entries: selected,
+    startSeq: selected[0]?.seqStart ?? null,
+    endSeq: bounds.maxSeq,
+    hasOlder: start > 0,
+    hasNewer: false,
+  };
+}
+
+export function selectReferenceProjectedTimelinePage(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 (!bounds) {
+    return {
+      entries: [],
+      startSeq: null,
+      endSeq: null,
+      hasOlder: false,
+      hasNewer: false,
+    };
+  }
+
+  if (projectedAll.length === 0) {
+    if (input.direction === "after") {
+      const cursorSeq = input.cursorSeq ?? bounds.minSeq - 1;
+      return {
+        entries: [],
+        startSeq: null,
+        endSeq: null,
+        hasOlder: cursorSeq >= bounds.minSeq,
+        hasNewer: cursorSeq < bounds.maxSeq,
+      };
+    }
+    if (input.direction === "before") {
+      const cursorSeq = input.cursorSeq ?? bounds.maxSeq + 1;
+      return {
+        entries: [],
+        startSeq: null,
+        endSeq: null,
+        hasOlder: cursorSeq > bounds.minSeq,
+        hasNewer: cursorSeq <= bounds.maxSeq,
+      };
+    }
+    return {
+      entries: [],
+      startSeq: null,
+      endSeq: null,
+      hasOlder: false,
+      hasNewer: false,
+    };
+  }
+
+  if (input.direction === "tail") {
+    return selectProjectedEntriesTail(projectedAll, limit, bounds);
+  }
+
+  if (input.direction === "after") {
+    const cursorSeq = input.cursorSeq ?? bounds.minSeq - 1;
+    const startSeq = Math.max(bounds.minSeq, cursorSeq + 1);
+    const selected = selectProjectedEntriesAfter({
+      entries: projectedAll,
+      startSeq,
+      maxSeq: bounds.maxSeq,
+      limit,
+    });
+    return {
+      entries: selected.entries,
+      startSeq: selected.endSeq === null ? null : startSeq,
+      endSeq: selected.endSeq,
+      hasOlder: startSeq > bounds.minSeq,
+      hasNewer: selected.endSeq !== null && selected.endSeq < bounds.maxSeq,
+    };
+  }
+
+  const cursorSeq = input.cursorSeq ?? bounds.maxSeq + 1;
+  const endSeq = Math.min(bounds.maxSeq, cursorSeq - 1);
+  if (endSeq < bounds.minSeq) {
+    return {
+      entries: [],
+      startSeq: null,
+      endSeq: null,
+      hasOlder: false,
+      hasNewer: endSeq < bounds.maxSeq,
+    };
+  }
+
+  const selected = selectProjectedEntriesBefore({ entries: projectedAll, endSeq, limit });
+  return {
+    entries: selected.entries,
+    startSeq: selected.startSeq,
+    endSeq,
+    hasOlder: selected.hasOlder,
+    hasNewer: endSeq < bounds.maxSeq,
+  };
+}
+
+// Existing selection fixtures exercise the retained owner through its public API.
+export function selectProjectedTimelinePage(
+  input: Parameters<typeof selectReferenceProjectedTimelinePage>[0],
+) {
+  const projection = new TimelineProjection(input.rows);
+  const bounds = input.bounds ?? getTimelineBounds(input.rows) ?? { minSeq: 0, maxSeq: 0 };
+  const page = projection.selectPage({ ...input, bounds });
+  return {
+    ...page,
+    entries: page.entries.map((row) => {
+      const { seq: _seq, ...entry } = row as ProjectedTimelineRow;
+      return entry;
+    }),
+  };
+}

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

@@ -1,9 +1,9 @@
+import { selectProjectedTimelinePage } from "./test-utils/timeline-page-reference.js";
 import { describe, expect, test } from "vitest";
 
 import type { AgentTimelineRow } from "./agent-manager.js";
 import {
   projectTimelineRows,
-  selectProjectedTimelinePage,
   selectTimelineWindowByProjectedLimit,
 } from "./timeline-projection.js";
 

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

@@ -295,12 +295,43 @@ function mergeAssistantChunks(entries: readonly WorkingEntry[]): WorkingEntry[]
 /** A retained item. `seq` is its latest source event, not its display anchor. */
 export type ProjectedTimelineRow = AgentTimelineRow & TimelineProjectionEntry;
 
+interface ProjectedTimelinePageOptions {
+  bounds: { minSeq: number; maxSeq: number };
+  direction: TimelineLimitDirection;
+  cursorSeq?: number;
+  limit?: number;
+}
+
 /** Owns projected state; source events are consumed, never retained. */
 export class TimelineProjection {
   private readonly rows: ProjectedTimelineRow[] = [];
   private readonly identities = new Map<string, number>();
+  private lastAssistantRowIndex: number | null = null;
+  // Disjoint source-coverage spans in display order. A tail starting inside a
+  // span must include its first anchor to cover interleaved lifecycle updates.
+  private readonly spans: { start: number; endSeq: number }[] = [];
+
+  private readonly sourceRanges: { startSeq: number; endSeq: number; rowIndex: number }[] = [];
+
+  constructor(rows: readonly AgentTimelineRow[] = []) {
+    for (const row of rows) this.appendProjected(row);
+    for (const [rowIndex, row] of this.rows.entries()) {
+      for (const range of row.sourceSeqRanges) this.sourceRanges.push({ ...range, rowIndex });
+    }
+    this.sourceRanges.sort((a, b) => a.startSeq - b.startSeq);
+  }
 
   append(row: AgentTimelineRow): void {
+    const rowIndex = this.appendProjected(row);
+    const last = this.sourceRanges.at(-1);
+    if (last && last.rowIndex === rowIndex && last.endSeq + 1 === row.seq) {
+      last.endSeq = row.seq;
+    } else {
+      this.sourceRanges.push({ startSeq: row.seq, endSeq: row.seq, rowIndex });
+    }
+  }
+
+  private appendProjected(row: AgentTimelineRow): number {
     const entry = makeCanonicalEntries([row])[0];
     const identity = timelineItemIdentity(row.item);
     const index = identity === null ? undefined : this.identities.get(identity);
@@ -308,7 +339,8 @@ export class TimelineProjection {
     const merged = existing ? mergeIdentityEntries(existing, entry) : null;
     if (merged && index !== undefined) {
       this.rows[index] = { ...merged, seq: merged.seqEnd };
-      return;
+      this.extendSpan(index);
+      return index;
     }
     const previous = this.rows.at(-1);
     const adjacent = previous
@@ -317,16 +349,159 @@ export class TimelineProjection {
     if (previous && adjacent.length === 1) {
       const mergedText = adjacent[0];
       this.rows[this.rows.length - 1] = { ...mergedText, seq: mergedText.seqEnd };
-      return;
+      this.extendSpan(this.rows.length - 1);
+      return this.rows.length - 1;
     }
     if (identity !== null) this.identities.set(identity, this.rows.length);
+    if (entry.item.type === "assistant_message") this.lastAssistantRowIndex = this.rows.length;
     this.rows.push({ ...entry, seq: entry.seqEnd });
+    const last = this.spans.at(-1);
+    if (last && last.endSeq >= entry.seqStart) {
+      last.endSeq = Math.max(last.endSeq, entry.seqEnd);
+    } else {
+      this.spans.push({ start: this.rows.length - 1, endSeq: entry.seqEnd });
+    }
+    return this.rows.length - 1;
+  }
+
+  private spanIndex(rowIndex: number): number {
+    let low = 0;
+    let high = this.spans.length;
+    while (low + 1 < high) {
+      const middle = (low + high) >>> 1;
+      if (this.spans[middle].start <= rowIndex) low = middle;
+      else high = middle;
+    }
+    return low;
+  }
+
+  private extendSpan(rowIndex: number): void {
+    const index = this.spanIndex(rowIndex);
+    const span = this.spans[index];
+    span.endSeq = Math.max(span.endSeq, this.rows[rowIndex].seqEnd);
+    let end = index + 1;
+    while (end < this.spans.length && this.rows[this.spans[end].start].seqStart <= span.endSeq) {
+      span.endSeq = Math.max(span.endSeq, this.spans[end].endSeq);
+      end++;
+    }
+    this.spans.splice(index + 1, end - index - 1);
   }
 
   getRows(): ProjectedTimelineRow[] {
     return this.rows.map((row) => ({ ...row }));
   }
 
+  selectPage(input: ProjectedTimelinePageOptions): ProjectedTimelinePageSelection {
+    if (this.rows.length === 0) {
+      const cursor =
+        input.cursorSeq ??
+        (input.direction === "before" ? input.bounds.maxSeq + 1 : input.bounds.minSeq - 1);
+      return {
+        entries: [],
+        startSeq: null,
+        endSeq: null,
+        hasOlder:
+          input.direction === "after"
+            ? cursor >= input.bounds.minSeq
+            : input.direction === "before" && cursor > input.bounds.minSeq,
+        hasNewer:
+          input.direction === "after"
+            ? cursor < input.bounds.maxSeq
+            : input.direction === "before" && cursor <= input.bounds.maxSeq,
+      };
+    }
+    switch (input.direction) {
+      case "tail":
+        return this.selectTail(input);
+      case "after":
+        return this.selectAfter(input);
+      case "before":
+        return this.selectBefore(input);
+    }
+  }
+
+  private selectTail(input: ProjectedTimelinePageOptions): ProjectedTimelinePageSelection {
+    const limit = Math.max(0, Math.floor(input.limit ?? 0));
+    const requestedStart = limit === 0 ? 0 : Math.max(0, this.rows.length - limit);
+    const start = this.spans[this.spanIndex(requestedStart)].start;
+    return {
+      entries: this.rows.slice(start),
+      startSeq: this.rows[start].seqStart,
+      endSeq: input.bounds.maxSeq,
+      hasOlder: start > 0,
+      hasNewer: false,
+    };
+  }
+
+  private selectAfter(input: ProjectedTimelinePageOptions): ProjectedTimelinePageSelection {
+    const startSeq = Math.max(
+      input.bounds.minSeq,
+      (input.cursorSeq ?? input.bounds.minSeq - 1) + 1,
+    );
+    let low = 0;
+    let high = this.sourceRanges.length;
+    while (low < high) {
+      const middle = (low + high) >>> 1;
+      if (this.sourceRanges[middle].endSeq < startSeq) low = middle + 1;
+      else high = middle;
+    }
+    const indexes = new Set<number>();
+    const limit = Math.max(0, Math.floor(input.limit ?? 0));
+    for (let i = low; i < this.sourceRanges.length; i++) {
+      const range = this.sourceRanges[i];
+      if (range.startSeq > input.bounds.maxSeq) break;
+      indexes.add(range.rowIndex);
+      if (limit > 0 && indexes.size === limit) break;
+    }
+    const entries = [...indexes].sort((a, b) => a - b).map((index) => this.rows[index]);
+    const selected = selectProjectedEntriesAfter({
+      entries,
+      startSeq,
+      maxSeq: input.bounds.maxSeq,
+      limit,
+    });
+    return {
+      entries: selected.entries,
+      startSeq: selected.endSeq === null ? null : startSeq,
+      endSeq: selected.endSeq,
+      hasOlder: startSeq > input.bounds.minSeq,
+      hasNewer: selected.endSeq !== null && selected.endSeq < input.bounds.maxSeq,
+    };
+  }
+
+  private selectBefore(input: ProjectedTimelinePageOptions): ProjectedTimelinePageSelection {
+    const endSeq = Math.min(input.bounds.maxSeq, (input.cursorSeq ?? input.bounds.maxSeq + 1) - 1);
+    if (endSeq >= input.bounds.minSeq) {
+      let low = 0;
+      let high = this.rows.length;
+      while (low < high) {
+        const middle = (low + high) >>> 1;
+        if (this.rows[middle].seqStart <= endSeq) low = middle + 1;
+        else high = middle;
+      }
+      const limit = Math.max(0, Math.floor(input.limit ?? 0));
+      const start = limit === 0 ? 0 : Math.max(0, low - limit);
+      return {
+        entries: this.rows.slice(start, low),
+        startSeq: this.rows[start]?.seqStart ?? null,
+        endSeq,
+        hasOlder: start > 0,
+        hasNewer: endSeq < input.bounds.maxSeq,
+      };
+    }
+    return { entries: [], startSeq: null, endSeq: null, hasOlder: false, hasNewer: true };
+  }
+
+  getLastItem(seq: number): AgentTimelineItem | null {
+    const last = this.sourceRanges.at(-1);
+    return last?.endSeq === seq ? this.rows[last.rowIndex].item : null;
+  }
+
+  getLastAssistantMessage(): string | null {
+    const row = this.lastAssistantRowIndex === null ? null : this.rows[this.lastAssistantRowIndex];
+    return row?.item.type === "assistant_message" ? row.item.text : null;
+  }
+
   enrichSubmittedUserMessage(
     clientMessageId: string,
     providerMessageId: string,
@@ -444,21 +619,6 @@ 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;
-  }
-  const entries = makeCanonicalEntries(rows);
-  return {
-    minSeq: entries.reduce((min, e) => Math.min(min, e.seqStart), Infinity),
-    maxSeq: entries.reduce((max, e) => Math.max(max, e.seqEnd), 0),
-  };
-}
-
 function firstSourceSeqInRange(
   entry: TimelineProjectionEntry,
   startSeq: number,
@@ -515,142 +675,6 @@ function selectProjectedEntriesAfter(input: {
   };
 }
 
-function selectProjectedEntriesBefore(input: {
-  entries: readonly TimelineProjectionEntry[];
-  endSeq: number;
-  limit: number;
-}): { entries: TimelineProjectionEntry[]; startSeq: number | null; hasOlder: boolean } {
-  // Older history follows projected display order. Lifecycle updates can move an
-  // entry's seqEnd without moving its display anchor, so seqStart keeps the full
-  // projected item on exactly one backward page.
-  const eligible = input.entries.filter((entry) => entry.seqStart <= input.endSeq);
-  const selected =
-    input.limit === 0 || input.limit >= eligible.length
-      ? eligible
-      : eligible.slice(eligible.length - input.limit);
-
-  return {
-    entries: selected,
-    startSeq: selected[0]?.seqStart ?? null,
-    hasOlder: selected.length < eligible.length,
-  };
-}
-
-function selectProjectedEntriesTail(
-  projectedAll: TimelineProjectionEntry[],
-  limit: number,
-  bounds: { minSeq: number; maxSeq: number },
-): ProjectedTimelinePageSelection {
-  let start = limit === 0 ? 0 : Math.max(0, projectedAll.length - limit);
-  // Include earlier display anchors with updates in the selected source window,
-  // so a tail certifies contiguous coverage even with interleaved tool updates.
-  for (let i = start - 1; i >= 0; i--) {
-    if (projectedAll[i].seqEnd >= projectedAll[start].seqStart) start = i;
-  }
-  const selected = projectedAll.slice(start);
-  return {
-    entries: selected,
-    startSeq: selected[0]?.seqStart ?? null,
-    endSeq: bounds.maxSeq,
-    hasOlder: start > 0,
-    hasNewer: false,
-  };
-}
-
-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 (!bounds) {
-    return {
-      entries: [],
-      startSeq: null,
-      endSeq: null,
-      hasOlder: false,
-      hasNewer: false,
-    };
-  }
-
-  if (projectedAll.length === 0) {
-    if (input.direction === "after") {
-      const cursorSeq = input.cursorSeq ?? bounds.minSeq - 1;
-      return {
-        entries: [],
-        startSeq: null,
-        endSeq: null,
-        hasOlder: cursorSeq >= bounds.minSeq,
-        hasNewer: cursorSeq < bounds.maxSeq,
-      };
-    }
-    if (input.direction === "before") {
-      const cursorSeq = input.cursorSeq ?? bounds.maxSeq + 1;
-      return {
-        entries: [],
-        startSeq: null,
-        endSeq: null,
-        hasOlder: cursorSeq > bounds.minSeq,
-        hasNewer: cursorSeq <= bounds.maxSeq,
-      };
-    }
-    return {
-      entries: [],
-      startSeq: null,
-      endSeq: null,
-      hasOlder: false,
-      hasNewer: false,
-    };
-  }
-
-  if (input.direction === "tail") {
-    return selectProjectedEntriesTail(projectedAll, limit, bounds);
-  }
-
-  if (input.direction === "after") {
-    const cursorSeq = input.cursorSeq ?? bounds.minSeq - 1;
-    const startSeq = Math.max(bounds.minSeq, cursorSeq + 1);
-    const selected = selectProjectedEntriesAfter({
-      entries: projectedAll,
-      startSeq,
-      maxSeq: bounds.maxSeq,
-      limit,
-    });
-    return {
-      entries: selected.entries,
-      startSeq: selected.endSeq === null ? null : startSeq,
-      endSeq: selected.endSeq,
-      hasOlder: startSeq > bounds.minSeq,
-      hasNewer: selected.endSeq !== null && selected.endSeq < bounds.maxSeq,
-    };
-  }
-
-  const cursorSeq = input.cursorSeq ?? bounds.maxSeq + 1;
-  const endSeq = Math.min(bounds.maxSeq, cursorSeq - 1);
-  if (endSeq < bounds.minSeq) {
-    return {
-      entries: [],
-      startSeq: null,
-      endSeq: null,
-      hasOlder: false,
-      hasNewer: endSeq < bounds.maxSeq,
-    };
-  }
-
-  const selected = selectProjectedEntriesBefore({ entries: projectedAll, endSeq, limit });
-  return {
-    entries: selected.entries,
-    startSeq: selected.startSeq,
-    endSeq,
-    hasOlder: selected.hasOlder,
-    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/atomic-file.test.ts

@@ -0,0 +1,147 @@
+import { promises as fs } from "node:fs";
+import os from "node:os";
+import path from "node:path";
+import { afterEach, beforeEach, expect, it } from "vitest";
+import { writeFileAtomic, writeJsonFileAtomic } from "./atomic-file.js";
+
+let directory: string;
+beforeEach(async () => {
+  directory = await fs.mkdtemp(path.join(os.tmpdir(), "paseo-atomic-file-"));
+});
+afterEach(async () => {
+  await fs.rm(directory, { recursive: true, force: true });
+});
+
+it.each(["EPERM", "EACCES", "EBUSY"])(
+  "commits a completed receipt after transient Windows %s replace failures",
+  async (code) => {
+    const file = path.join(directory, "receipt.json");
+    await writeJsonFileAtomic(file, { state: "pending" });
+    let failures = 3;
+    let elapsed = 0;
+    await writeJsonFileAtomic(
+      file,
+      { state: "completed" },
+      {
+        platform: "win32",
+        now: () => elapsed,
+        sleep: async (milliseconds) => {
+          elapsed += milliseconds;
+        },
+        rename: async (source, destination) => {
+          if (failures-- > 0) {
+            expect(JSON.parse(await fs.readFile(destination, "utf8"))).toEqual({
+              state: "pending",
+            });
+            expect(JSON.parse(await fs.readFile(source, "utf8"))).toEqual({ state: "completed" });
+            throw Object.assign(new Error("destination held open"), { code });
+          }
+          await fs.rename(source, destination);
+        },
+      },
+    );
+    expect(JSON.parse(await fs.readFile(file, "utf8"))).toEqual({ state: "completed" });
+    expect(await fs.readdir(directory)).toEqual(["receipt.json"]);
+    expect(elapsed).toBeGreaterThan(0);
+  },
+);
+
+it.each(["EPERM", "EACCES", "EBUSY"])(
+  "preserves the previous file and removes the temp file when Windows %s persists",
+  async (code) => {
+    const file = path.join(directory, "receipt.json");
+    await writeJsonFileAtomic(file, { state: "pending" });
+    const error = Object.assign(new Error("destination held open"), { code });
+    const waits: number[] = [];
+    let elapsed = 0;
+    const attempts: number[] = [];
+    await expect(
+      writeJsonFileAtomic(
+        file,
+        { state: "completed" },
+        {
+          platform: "win32",
+          now: () => elapsed,
+          sleep: async (milliseconds) => {
+            waits.push(milliseconds);
+            elapsed += milliseconds;
+          },
+          rename: async () => {
+            attempts.push(elapsed);
+            throw error;
+          },
+        },
+      ),
+    ).rejects.toBe(error);
+    expect(elapsed).toBe(1000);
+    expect(waits.slice(0, 5)).toEqual([10, 20, 40, 80, 100]);
+    expect(Math.max(...waits)).toBe(100);
+    expect(attempts.every((time) => time < 1000)).toBe(true);
+    expect(JSON.parse(await fs.readFile(file, "utf8"))).toEqual({ state: "pending" });
+    expect(await fs.readdir(directory)).toEqual(["receipt.json"]);
+  },
+);
+
+it.each([
+  ["linux", "EPERM"],
+  ["darwin", "EACCES"],
+  ["linux", "EBUSY"],
+  ["win32", "ENOENT"],
+  ["win32", "ENOSPC"],
+  ["win32", "EXDEV"],
+] as const)("does not retry %s %s failures", async (platform, code) => {
+  const file = path.join(directory, "receipt.json");
+  await writeJsonFileAtomic(file, { state: "pending" });
+  const error = Object.assign(new Error("rename failed"), { code });
+  let attempts = 0;
+  const waits: number[] = [];
+  await expect(
+    writeFileAtomic(file, "replacement", {
+      platform,
+      now: () => 0,
+      sleep: async (milliseconds) => {
+        waits.push(milliseconds);
+      },
+      rename: async () => {
+        attempts++;
+        throw error;
+      },
+    }),
+  ).rejects.toBe(error);
+  expect(attempts).toBe(1);
+  expect(waits).toEqual([]);
+  expect(JSON.parse(await fs.readFile(file, "utf8"))).toEqual({ state: "pending" });
+  expect(await fs.readdir(directory)).toEqual(["receipt.json"]);
+});
+
+it("does not retry after a rename consumes the Windows retry budget", async () => {
+  const file = path.join(directory, "receipt.json");
+  const error = Object.assign(new Error("slow rename failed"), { code: "EPERM" });
+  let elapsed = 0;
+  const waits: number[] = [];
+  await expect(
+    writeFileAtomic(file, "replacement", {
+      platform: "win32",
+      now: () => elapsed,
+      sleep: async (milliseconds) => {
+        waits.push(milliseconds);
+      },
+      rename: async () => {
+        elapsed += 1000;
+        throw error;
+      },
+    }),
+  ).rejects.toBe(error);
+  expect(waits).toEqual([]);
+  expect(await fs.readdir(directory)).toEqual([]);
+});
+
+it("creates parent directories and replaces binary and JSON files through the default runtime", async () => {
+  const file = path.join(directory, "nested", "file");
+  const bytes = Buffer.from([0, 255, 128, 1]);
+  await writeFileAtomic(file, bytes);
+  expect(await fs.readFile(file)).toEqual(bytes);
+  await writeJsonFileAtomic(file, { state: "completed" });
+  expect(await fs.readFile(file, "utf8")).toBe('{\n  "state": "completed"\n}');
+  expect(await fs.readdir(path.dirname(file))).toEqual(["file"]);
+});

packages/server/src/server/atomic-file.ts

@@ -1,10 +1,26 @@
 import { randomUUID } from "node:crypto";
 import { promises as fs } from "node:fs";
 import path from "node:path";
+import { setTimeout as sleep } from "node:timers/promises";
+
+interface AtomicFileRuntime {
+  platform: NodeJS.Platform;
+  rename: (source: string, destination: string) => Promise<void>;
+  now: () => number;
+  sleep: (milliseconds: number) => Promise<void>;
+}
+
+const runtime: AtomicFileRuntime = {
+  platform: process.platform,
+  rename: fs.rename,
+  now: () => performance.now(),
+  sleep,
+};
 
 export async function writeFileAtomic(
   filePath: string,
   data: string | NodeJS.ArrayBufferView,
+  operations: AtomicFileRuntime = runtime,
 ): Promise<void> {
   await fs.mkdir(path.dirname(filePath), { recursive: true });
   const tempPath = path.join(
@@ -13,13 +29,48 @@ export async function writeFileAtomic(
   );
   try {
     await fs.writeFile(tempPath, data, "utf8");
-    await fs.rename(tempPath, filePath);
+    await replaceFile(tempPath, filePath, operations);
   } catch (error) {
     await fs.rm(tempPath, { force: true });
     throw error;
   }
 }
 
-export async function writeJsonFileAtomic(filePath: string, value: unknown): Promise<void> {
-  await writeFileAtomic(filePath, JSON.stringify(value, null, 2));
+async function replaceFile(
+  source: string,
+  destination: string,
+  operations: AtomicFileRuntime,
+): Promise<void> {
+  // Windows readers/scanners can briefly deny replacement. Yield with backoff,
+  // but keep interactive persistence failures bounded to a one-second retry budget.
+  const deadline = operations.now() + 1000;
+  let delay = 10;
+  for (;;) {
+    try {
+      await operations.rename(source, destination);
+      return;
+    } catch (error) {
+      if (
+        operations.platform !== "win32" ||
+        !(error instanceof Error) ||
+        !("code" in error) ||
+        !["EPERM", "EACCES", "EBUSY"].includes(String(error.code))
+      ) {
+        throw error;
+      }
+      const remaining = deadline - operations.now();
+      if (remaining <= 0) throw error;
+      await operations.sleep(Math.min(delay, remaining));
+      if (operations.now() >= deadline) throw error;
+      delay = Math.min(delay * 2, 100);
+    }
+  }
+}
+
+export async function writeJsonFileAtomic(
+  filePath: string,
+  value: unknown,
+  operations: AtomicFileRuntime = runtime,
+): Promise<void> {
+  await writeFileAtomic(filePath, JSON.stringify(value, null, 2), operations);
 }

packages/server/src/server/daemon-e2e/cli-logs-follow.e2e.test.ts

@@ -87,3 +87,53 @@ test("logs --follow preserves the same assistant text as one-shot logs", async (
     await daemon.close();
   }
 }, 60_000);
+
+test("omitted after limit pages forward while explicit zero preserves complete CLI history", async () => {
+  const daemon = await createTestPaseoDaemon();
+  const client = new DaemonClient({ url: `ws://127.0.0.1:${daemon.port}/ws` });
+  try {
+    await client.connect();
+    await client.fetchAgents({ subscribe: {} });
+    const agent = await client.createAgent({ provider: "claude", cwd: daemon.paseoHome });
+    const initial = await client.fetchAgentTimeline(agent.id, { direction: "tail", limit: 0 });
+    const cursor = { epoch: initial.epoch, seq: initial.window.maxSeq };
+    for (let index = 0; index < 451; index++) {
+      await daemon.daemon.agentManager.appendTimelineItem(agent.id, {
+        type: "user_message",
+        text: String(index),
+      });
+    }
+    const first = await client.fetchAgentTimeline(agent.id, { direction: "after", cursor });
+    expect(first.entries).toHaveLength(200);
+    expect(first.hasNewer).toBe(true);
+    expect(first.endCursor).toEqual({ epoch: cursor.epoch, seq: cursor.seq + 200 });
+    const second = await client.fetchAgentTimeline(agent.id, {
+      direction: "after",
+      cursor: first.endCursor!,
+    });
+    const third = await client.fetchAgentTimeline(agent.id, {
+      direction: "after",
+      cursor: second.endCursor!,
+    });
+    expect(second.entries).toHaveLength(200);
+    expect(third.entries).toHaveLength(51);
+    expect(third.hasNewer).toBe(false);
+    expect(
+      [...first.entries, ...second.entries, ...third.entries].map((entry) => entry.item),
+    ).toEqual(
+      Array.from({ length: 451 }, (_, index) => ({ type: "user_message", text: String(index) })),
+    );
+    const allAfter = await client.fetchAgentTimeline(agent.id, {
+      direction: "after",
+      cursor,
+      limit: 0,
+    });
+    const allTail = await client.fetchAgentTimeline(agent.id, { direction: "tail", limit: 0 });
+    expect(allAfter.entries).toHaveLength(451);
+    expect(allAfter.hasNewer).toBe(false);
+    expect(allTail.entries).toHaveLength(initial.entries.length + 451);
+  } finally {
+    await client.close();
+    await daemon.close();
+  }
+}, 60_000);

packages/server/src/server/session.ts

@@ -7787,8 +7787,6 @@ export class Session {
   ): Promise<void> {
     const direction: AgentTimelineFetchDirection = msg.direction ?? (msg.cursor ? "after" : "tail");
     const projection = "projected" as const;
-    const requestedLimit = msg.limit;
-    const pageLimit = requestedLimit ?? (direction === "after" ? 0 : 200);
     const cursor: AgentTimelineCursor | undefined = msg.cursor
       ? {
           epoch: msg.cursor.epoch,
@@ -7807,7 +7805,7 @@ export class Session {
       const fetchedControlTimeline = this.agentManager.fetchTimeline(msg.agentId, {
         direction,
         cursor,
-        limit: pageLimit,
+        limit: msg.limit,
       });
       const selectedTimeline = {
         timeline: fetchedControlTimeline,