Fix agent turn timing persistence

packages/app/e2e/agent-stream-ui.spec.ts

@@ -6,6 +6,7 @@ import {
   expectTurnCopyButton,
   expectScrollFollowsNewContent,
 } from "./helpers/agent-stream";
+import { clickNewChat } from "./helpers/launcher";
 import { startRunningMockAgent } from "./helpers/composer";
 
 test.describe("Agent stream UI", () => {
@@ -42,4 +43,23 @@ test.describe("Agent stream UI", () => {
       await repo.cleanup();
     }
   });
+
+  test("shows elapsed timer on first app-created running turn", async ({ page, withWorkspace }) => {
+    test.setTimeout(90_000);
+    const workspace = await withWorkspace({ prefix: "stream-first-app-turn-timer-" });
+    await workspace.navigateTo();
+    await clickNewChat(page);
+    await page.getByText("Model defaults are still loading").waitFor({
+      state: "hidden",
+      timeout: 30_000,
+    });
+    const prompt = "Stream briefly for first app-created turn timer test.";
+    const composer = page.getByRole("textbox", { name: "Message agent..." }).first();
+    await composer.fill(prompt);
+    await page.getByRole("button", { name: "Send message" }).click();
+    await page.getByText(prompt, { exact: true }).first().waitFor({ state: "visible" });
+    await awaitAssistantMessage(page);
+    await expectInlineWorkingIndicator(page);
+    await page.getByTestId("turn-working-elapsed").waitFor({ state: "visible", timeout: 5_000 });
+  });
 });

packages/app/src/components/agent-stream-render-model.test.ts

@@ -35,6 +35,7 @@ describe("buildAgentStreamRenderModel", () => {
     const head = [assistantMessage("live-a", 121)];
 
     const model = buildAgentStreamRenderModel({
+      agentStatus: "running",
       tail,
       head,
       platform: "web",
@@ -52,6 +53,7 @@ describe("buildAgentStreamRenderModel", () => {
     const head = [assistantMessage("live-a", 3)];
 
     const model = buildAgentStreamRenderModel({
+      agentStatus: "running",
       tail,
       head,
       platform: "web",
@@ -69,12 +71,14 @@ describe("buildAgentStreamRenderModel", () => {
     const secondHead = [assistantMessage("live-b", 4)];
 
     const first = buildAgentStreamRenderModel({
+      agentStatus: "running",
       tail,
       head: firstHead,
       platform: "native",
       isMobileBreakpoint: false,
     });
     const second = buildAgentStreamRenderModel({
+      agentStatus: "running",
       tail,
       head: secondHead,
       platform: "native",
@@ -85,4 +89,73 @@ describe("buildAgentStreamRenderModel", () => {
     expect(first.segments.historyMounted).toBe(second.segments.historyMounted);
     expect(second.segments.liveHead.map((item) => item.id)).toEqual(["live-b"]);
   });
+
+  it("derives running turn timing across committed history and live head", () => {
+    const tail = [userMessage("u1", 1)];
+    const head = [assistantMessage("live-a", 4)];
+
+    const model = buildAgentStreamRenderModel({
+      agentStatus: "running",
+      tail,
+      head,
+      platform: "web",
+      isMobileBreakpoint: false,
+    });
+
+    expect(model.turnTiming.runningStartedAt).toBe(tail[0]?.timestamp);
+    expect(model.turnTiming.byAssistantId.has("live-a")).toBe(false);
+  });
+
+  it("maps completed turn timing to assistant ids across committed history and live head", () => {
+    const tail = [userMessage("u1", 1)];
+    const head = [assistantMessage("live-a", 4)];
+
+    const model = buildAgentStreamRenderModel({
+      agentStatus: "idle",
+      tail,
+      head,
+      platform: "web",
+      isMobileBreakpoint: false,
+    });
+
+    expect(model.turnTiming.runningStartedAt).toBe(null);
+    expect(model.turnTiming.byAssistantId.get("live-a")).toEqual({
+      startedAt: tail[0]?.timestamp,
+      completedAt: head[0]?.timestamp,
+      durationMs: 3000,
+    });
+  });
+
+  it("derives the same timing for native inverted rendering", () => {
+    const tail = [userMessage("u1", 1), assistantMessage("a1", 4)];
+
+    const model = buildAgentStreamRenderModel({
+      agentStatus: "idle",
+      tail,
+      head: [],
+      platform: "native",
+      isMobileBreakpoint: false,
+    });
+
+    expect(model.segments.historyMounted.map((item) => item.id)).toEqual(["a1", "u1"]);
+    expect(model.turnTiming.byAssistantId.get("a1")).toEqual({
+      startedAt: tail[0]?.timestamp,
+      completedAt: tail[1]?.timestamp,
+      durationMs: 3000,
+    });
+  });
+
+  it("does not create completed timing for adjacent user messages", () => {
+    const tail = [userMessage("u1", 1), userMessage("u2", 4)];
+
+    const model = buildAgentStreamRenderModel({
+      agentStatus: "idle",
+      tail,
+      head: [],
+      platform: "web",
+      isMobileBreakpoint: false,
+    });
+
+    expect(model.turnTiming.byAssistantId.size).toBe(0);
+  });
 });

packages/app/src/components/agent-stream-render-model.ts

@@ -1,4 +1,5 @@
 import type { ReactNode } from "react";
+import { deriveStreamTurnTiming, type StreamTurnTiming } from "@/timeline/turn-time";
 import type { StreamItem } from "@/types/stream";
 import {
   findMountedWindowStart,
@@ -32,11 +33,13 @@ export interface StreamRenderAuxiliary {
 export interface AgentStreamRenderModel {
   history: StreamItem[];
   segments: StreamRenderSegments;
+  turnTiming: StreamTurnTiming;
   boundary: StreamHistoryBoundary;
   auxiliary: StreamRenderAuxiliary;
 }
 
 export interface BuildAgentStreamRenderModelInput {
+  agentStatus: string;
   tail: StreamItem[];
   head: StreamItem[];
   platform: "web" | "native";
@@ -55,6 +58,10 @@ const splitHistoryCache = new WeakMap<
   StreamItem[],
   Map<string, Pick<AgentStreamRenderModel, "history" | "segments">>
 >();
+const turnTimingCache = new WeakMap<
+  StreamItem[],
+  WeakMap<StreamItem[], Map<string, StreamTurnTiming>>
+>();
 
 function getOrderedItems(params: {
   cache: WeakMap<StreamItem[], Map<string, StreamItem[]>>;
@@ -127,6 +134,30 @@ function splitOrderedTail(params: {
   return split;
 }
 
+function getTurnTiming(params: {
+  agentStatus: string;
+  tail: StreamItem[];
+  head: StreamItem[];
+}): StreamTurnTiming {
+  let cachedByHead = turnTimingCache.get(params.tail);
+  if (!cachedByHead) {
+    cachedByHead = new WeakMap();
+    turnTimingCache.set(params.tail, cachedByHead);
+  }
+  let cachedByStatus = cachedByHead.get(params.head);
+  if (!cachedByStatus) {
+    cachedByStatus = new Map();
+    cachedByHead.set(params.head, cachedByStatus);
+  }
+  const cached = cachedByStatus.get(params.agentStatus);
+  if (cached) {
+    return cached;
+  }
+  const timing = deriveStreamTurnTiming(params);
+  cachedByStatus.set(params.agentStatus, timing);
+  return timing;
+}
+
 export function buildAgentStreamRenderModel(
   input: BuildAgentStreamRenderModelInput,
 ): AgentStreamRenderModel {
@@ -160,6 +191,11 @@ export function buildAgentStreamRenderModel(
     platform: input.platform,
     isMobileBreakpoint: input.isMobileBreakpoint,
   });
+  const turnTiming = getTurnTiming({
+    agentStatus: input.agentStatus,
+    tail: input.tail,
+    head: input.head,
+  });
 
   return {
     history: splitHistory.history,
@@ -167,6 +203,7 @@ export function buildAgentStreamRenderModel(
       ...splitHistory.segments,
       liveHead: orderedHead,
     },
+    turnTiming,
     boundary: {
       hasVirtualizedHistory: splitHistory.segments.historyVirtualized.length > 0,
       hasMountedHistory: splitHistory.segments.historyMounted.length > 0,

packages/app/src/components/agent-stream-turn-footer.tsx

@@ -10,7 +10,7 @@ import Animated, {
 } from "react-native-reanimated";
 import { StyleSheet } from "react-native-unistyles";
 import { MAX_CONTENT_WIDTH } from "@/constants/layout";
-import { findTurnHeaderForAssistantTurn } from "@/timeline/turn-time";
+import type { TurnTiming } from "@/timeline/turn-time";
 import type { StreamItem } from "@/types/stream";
 import {
   getWorkingIndicatorDotStrength,
@@ -28,6 +28,7 @@ export type TurnContentStrategy = StreamStrategy;
 export interface TurnFooterHost {
   itemId: string;
   items: StreamItem[];
+  timing?: TurnTiming;
   startIndex: number;
 }
 
@@ -36,11 +37,13 @@ export function resolveBottomTurnFooterHost(input: {
   history: StreamItem[];
   liveHead: StreamItem[];
   isInverted: boolean;
+  timingByAssistantId: Map<string, TurnTiming>;
 }): TurnFooterHost | null {
   if (input.agentStatus === "running") {
     return null;
   }
-  const footerItems = input.liveHead.length > 0 ? input.liveHead : input.history;
+  const usesLiveHead = input.liveHead.length > 0;
+  const footerItems = usesLiveHead ? input.liveHead : input.history;
   const startIndex = input.isInverted ? 0 : footerItems.length - 1;
   const item = footerItems[startIndex];
   if (!item || item.kind !== "assistant_message") {
@@ -49,6 +52,7 @@ export function resolveBottomTurnFooterHost(input: {
   return {
     itemId: item.id,
     items: footerItems,
+    timing: input.timingByAssistantId.get(item.id),
     startIndex,
   };
 }
@@ -89,22 +93,34 @@ export const TurnFooter = memo(function TurnFooter({
     return null;
   }
   return (
-    <CompletedTurnFooterRow strategy={strategy} items={host.items} startIndex={host.startIndex} />
+    <CompletedTurnFooterRow
+      strategy={strategy}
+      items={host.items}
+      timing={host.timing}
+      startIndex={host.startIndex}
+    />
   );
 });
 
 export const CompletedTurnFooterRow = memo(function CompletedTurnFooterRow({
   strategy,
   items,
+  timing,
   startIndex,
 }: {
   strategy: TurnContentStrategy;
   items: StreamItem[];
+  timing?: TurnTiming;
   startIndex: number;
 }) {
   return (
     <TurnFooterRow>
-      <CompletedTurnFooter strategy={strategy} items={items} startIndex={startIndex} />
+      <CompletedTurnFooter
+        strategy={strategy}
+        items={items}
+        timing={timing}
+        startIndex={startIndex}
+      />
     </TurnFooterRow>
   );
 });
@@ -194,10 +210,12 @@ function RunningTurnFooter({ inFlightTurnStartedAt }: { inFlightTurnStartedAt: D
 function CompletedTurnFooter({
   strategy,
   items,
+  timing,
   startIndex,
 }: {
   strategy: TurnContentStrategy;
   items: StreamItem[];
+  timing?: TurnTiming;
   startIndex: number;
 }) {
   const getContent = useCallback(
@@ -209,16 +227,12 @@ function CompletedTurnFooter({
       }),
     [strategy, items, startIndex],
   );
-  const header = useMemo(
-    () => findTurnHeaderForAssistantTurn({ strategy, items, startIndex }),
-    [strategy, items, startIndex],
-  );
   return (
     <View style={stylesheet.turnFooterSlot}>
       <AssistantTurnFooter
         getContent={getContent}
-        startedAt={header?.startedAt}
-        durationMs={header?.durationMs}
+        completedAt={timing?.completedAt}
+        durationMs={timing?.durationMs}
       />
     </View>
   );

packages/app/src/components/agent-stream-view.tsx

@@ -21,7 +21,7 @@ import {
   type ViewStyle,
 } from "react-native";
 import { StyleSheet, withUnistyles } from "react-native-unistyles";
-import { useIsCompactFormFactor } from "@/constants/layout";
+import { MAX_CONTENT_WIDTH, useIsCompactFormFactor } from "@/constants/layout";
 import { useMutation } from "@tanstack/react-query";
 import Animated, { FadeIn, FadeOut } from "react-native-reanimated";
 import { Check, ChevronDown, X } from "lucide-react-native";
@@ -74,12 +74,10 @@ import {
   type BottomAnchorLocalRequest,
   type BottomAnchorRouteRequest,
 } from "./use-bottom-anchor-controller";
-import { MAX_CONTENT_WIDTH } from "@/constants/layout";
 import { normalizeInlinePathTarget } from "@/utils/inline-path";
 import { resolveWorkspaceIdByExecutionDirectory } from "@/utils/workspace-execution";
 import { navigateToPreparedWorkspaceTab } from "@/utils/workspace-navigation";
 import { useStableEvent } from "@/hooks/use-stable-event";
-import { findInFlightTurnStartedAt } from "@/timeline/turn-time";
 import { isWeb } from "@/constants/platform";
 import type { Theme } from "@/styles/theme";
 
@@ -129,6 +127,7 @@ function renderStreamItemWithTurnFooter(input: {
   item: StreamItem;
   nextItem: StreamItem | undefined;
   items: StreamItem[];
+  timing: AgentStreamRenderModel["turnTiming"]["byAssistantId"];
   index: number;
   agentStatus: string;
   suppressTurnFooter: boolean | undefined;
@@ -155,6 +154,7 @@ function renderStreamItemWithTurnFooter(input: {
         <CompletedTurnFooterRow
           strategy={input.strategy}
           items={input.items}
+          timing={input.timing.get(input.item.id)}
           startIndex={input.index}
         />
       ) : null}
@@ -245,6 +245,8 @@ export interface AgentStreamViewProps {
   onOpenWorkspaceFile?: (input: { filePath: string }) => void;
 }
 
+const EMPTY_STREAM_HEAD: StreamItem[] = [];
+
 const AgentStreamViewComponent = forwardRef<AgentStreamViewHandle, AgentStreamViewProps>(
   function AgentStreamView(
     {
@@ -386,21 +388,13 @@ const AgentStreamViewComponent = forwardRef<AgentStreamViewHandle, AgentStreamVi
 
     const baseRenderModel = useMemo(() => {
       return buildAgentStreamRenderModel({
+        agentStatus: agent.status,
         tail: streamItems,
-        head: streamHead ?? [],
+        head: streamHead ?? EMPTY_STREAM_HEAD,
         platform: isWeb ? "web" : "native",
         isMobileBreakpoint: isMobile,
       });
-    }, [isMobile, streamHead, streamItems]);
-    const inFlightTurnStartedAt = useMemo(
-      () =>
-        findInFlightTurnStartedAt({
-          agentStatus: agent.status,
-          liveHead: baseRenderModel.segments.liveHead,
-          tail: streamItems,
-        }),
-      [agent.status, baseRenderModel.segments.liveHead, streamItems],
-    );
+    }, [agent.status, isMobile, streamHead, streamItems]);
     useImperativeHandle(
       ref,
       () => ({
@@ -643,12 +637,6 @@ const AgentStreamViewComponent = forwardRef<AgentStreamViewHandle, AgentStreamVi
               />
             );
 
-          case "turn_header":
-            // Purely a data carrier - duration renders next to the assistant
-            // turn's copy button (CompletedTurnFooter), and the in-flight
-            // ticker renders next to the WorkingIndicator dots.
-            return null;
-
           default:
             return null;
         }
@@ -662,11 +650,13 @@ const AgentStreamViewComponent = forwardRef<AgentStreamViewHandle, AgentStreamVi
         history: baseRenderModel.history,
         liveHead: baseRenderModel.segments.liveHead,
         isInverted: streamRenderStrategy.getFlatListInverted(),
+        timingByAssistantId: baseRenderModel.turnTiming.byAssistantId,
       });
     }, [
       agent.status,
       baseRenderModel.history,
       baseRenderModel.segments.liveHead,
+      baseRenderModel.turnTiming.byAssistantId,
       streamRenderStrategy,
     ]);
 
@@ -689,13 +679,19 @@ const AgentStreamViewComponent = forwardRef<AgentStreamViewHandle, AgentStreamVi
           item,
           nextItem,
           items,
+          timing: baseRenderModel.turnTiming.byAssistantId,
           index,
           agentStatus: agent.status,
           suppressTurnFooter: seams.suppressTurnFooter,
           strategy: streamRenderStrategy,
         });
       },
-      [renderStreamItemContent, agent.status, streamRenderStrategy],
+      [
+        agent.status,
+        baseRenderModel.turnTiming.byAssistantId,
+        renderStreamItemContent,
+        streamRenderStrategy,
+      ],
     );
 
     const pendingPermissionItems = useMemo(
@@ -717,12 +713,17 @@ const AgentStreamViewComponent = forwardRef<AgentStreamViewHandle, AgentStreamVi
         showRunningTurnFooter || bottomTurnFooterHost ? (
           <TurnFooter
             isRunning={showRunningTurnFooter}
-            inFlightTurnStartedAt={inFlightTurnStartedAt}
+            inFlightTurnStartedAt={baseRenderModel.turnTiming.runningStartedAt}
             host={bottomTurnFooterHost}
             strategy={streamRenderStrategy}
           />
         ) : null,
-      [showRunningTurnFooter, inFlightTurnStartedAt, bottomTurnFooterHost, streamRenderStrategy],
+      [
+        showRunningTurnFooter,
+        baseRenderModel.turnTiming.runningStartedAt,
+        bottomTurnFooterHost,
+        streamRenderStrategy,
+      ],
     );
     const renderModel = useMemo<AgentStreamRenderModel>(() => {
       return {
@@ -748,7 +749,6 @@ const AgentStreamViewComponent = forwardRef<AgentStreamViewHandle, AgentStreamVi
     );
 
     const historyItems = renderModel.history;
-    const _liveHeadItems = renderModel.segments.liveHead;
     const { boundary, auxiliary } = renderModel;
     const lastHistoryItem = historyItems.at(-1) ?? null;
     const firstLiveHeadItem = renderModel.segments.liveHead[0] ?? null;

packages/app/src/components/message.tsx

@@ -557,7 +557,7 @@ export const UserMessage = memo(function UserMessage({
 
 interface AssistantTurnFooterProps {
   getContent: () => string;
-  startedAt?: Date;
+  completedAt?: Date;
   durationMs?: number;
 }
 
@@ -595,13 +595,13 @@ const TIMESTAMP_REVEAL_MS = 3000;
 
 /**
  * Footer rendered next to the copy button at the end of an assistant turn.
- * Always shows the turn duration; swaps to the start timestamp on hover (web)
+ * Always shows the turn duration; swaps to the end timestamp on hover (web)
  * or tap (native). The hidden sizer keeps the label width stable while the
  * visible text swaps.
  */
 export const AssistantTurnFooter = memo(function AssistantTurnFooter({
   getContent,
-  startedAt,
+  completedAt,
   durationMs,
 }: AssistantTurnFooterProps) {
   const [hovered, setHovered] = useState(false);
@@ -622,8 +622,8 @@ export const AssistantTurnFooter = memo(function AssistantTurnFooter({
     [durationMs],
   );
   const timestampLabel = useMemo(
-    () => (startedAt ? formatMessageTimestamp(startedAt) : ""),
-    [startedAt],
+    () => (completedAt ? formatMessageTimestamp(completedAt) : ""),
+    [completedAt],
   );
 
   const canSwap = Boolean(timestampLabel);
@@ -655,9 +655,7 @@ export const AssistantTurnFooter = memo(function AssistantTurnFooter({
           onHoverIn={handleHoverIn}
           onHoverOut={handleHoverOut}
           accessibilityRole={canSwap ? "button" : undefined}
-          accessibilityLabel={
-            canSwap ? `${durationLabel}, started ${timestampLabel}` : durationLabel
-          }
+          accessibilityLabel={canSwap ? `${durationLabel}, ended ${timestampLabel}` : durationLabel}
         >
           <View style={assistantTurnFooterStylesheet.labelWrapper}>
             {/* Sizer reserves space for whichever label is longer so the

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

@@ -1,4 +1,3 @@
-import invariant from "tiny-invariant";
 import { describe, expect, it } from "vitest";
 import type { AgentStreamEventPayload } from "@server/shared/messages";
 import type { StreamItem } from "@/types/stream";
@@ -241,12 +240,10 @@ describe("processTimelineResponse", () => {
     });
 
     const user = result.tail.find((item) => item.kind === "user_message");
-    const header = result.tail.find((item) => item.kind === "turn_header");
+    const assistant = result.tail.find((item) => item.kind === "assistant_message");
 
     expect(user?.timestamp.toISOString()).toBe("2025-01-01T12:00:03.000Z");
-    invariant(header?.kind === "turn_header");
-    expect(header.startedAt.toISOString()).toBe("2025-01-01T12:00:04.000Z");
-    expect(header.completedAt?.toISOString()).toBe("2025-01-01T12:00:04.000Z");
+    expect(assistant?.timestamp.toISOString()).toBe("2025-01-01T12:00:04.000Z");
   });
 
   it("sets cursor to null when reset=true but no cursors in payload", () => {

packages/app/src/timeline/turn-time.test.ts

@@ -0,0 +1,87 @@
+import assert from "node:assert/strict";
+import { describe, it } from "vitest";
+import { deriveStreamTurnTiming } from "./turn-time";
+import type { StreamItem } from "@/types/stream";
+
+function user(id: string, timestamp: Date): StreamItem {
+  return {
+    kind: "user_message",
+    id,
+    text: id,
+    timestamp,
+  };
+}
+
+function assistant(id: string, timestamp: Date): StreamItem {
+  return {
+    kind: "assistant_message",
+    id,
+    text: id,
+    timestamp,
+  };
+}
+
+describe("deriveStreamTurnTiming", () => {
+  it("uses the last user message as the running turn start", () => {
+    const firstUserAt = new Date("2026-05-15T00:00:00.000Z");
+    const secondUserAt = new Date("2026-05-15T00:01:00.000Z");
+
+    const timing = deriveStreamTurnTiming({
+      agentStatus: "running",
+      tail: [
+        user("u1", firstUserAt),
+        assistant("a1", new Date("2026-05-15T00:00:05.000Z")),
+        user("u2", secondUserAt),
+      ],
+      head: [assistant("a2", new Date("2026-05-15T00:01:04.000Z"))],
+    });
+
+    assert.equal(timing.runningStartedAt, secondUserAt);
+    assert.equal(timing.byAssistantId.has("a2"), false);
+  });
+
+  it("derives completed turn timing from user and assistant item timestamps", () => {
+    const userAt = new Date("2026-05-15T00:00:00.000Z");
+    const assistantAt = new Date("2026-05-15T00:00:07.000Z");
+
+    const timing = deriveStreamTurnTiming({
+      agentStatus: "idle",
+      tail: [
+        user("u1", userAt),
+        assistant("a1", assistantAt),
+        user("u2", new Date("2026-05-15T00:01:00.000Z")),
+      ],
+      head: [],
+    });
+
+    assert.deepEqual(timing.byAssistantId.get("a1"), {
+      startedAt: userAt,
+      completedAt: assistantAt,
+      durationMs: 7000,
+    });
+  });
+
+  it("maps multiple assistant chunks in one turn to the same timing", () => {
+    const userAt = new Date("2026-05-15T00:00:00.000Z");
+    const firstAssistantAt = new Date("2026-05-15T00:00:03.000Z");
+    const lastAssistantAt = new Date("2026-05-15T00:00:07.000Z");
+
+    const timing = deriveStreamTurnTiming({
+      agentStatus: "idle",
+      tail: [
+        user("u1", userAt),
+        assistant("a1", firstAssistantAt),
+        assistant("a2", lastAssistantAt),
+      ],
+      head: [],
+    });
+
+    const expected = {
+      startedAt: userAt,
+      completedAt: lastAssistantAt,
+      durationMs: 7000,
+    };
+    assert.deepEqual(timing.byAssistantId.get("a1"), expected);
+    assert.deepEqual(timing.byAssistantId.get("a2"), expected);
+  });
+});

packages/app/src/timeline/turn-time.ts

@@ -1,146 +1,83 @@
-import type { StreamItem, TurnHeaderItem, TurnHeaderOutcome } from "@/types/stream";
+import type { StreamItem } from "@/types/stream";
 
-export function appendLiveTurnHeader(state: StreamItem[], startedAt: Date): StreamItem[] {
-  const lastHeader = findLastTurnHeader(state);
-  if (lastHeader && lastHeader.completedAt === undefined) {
-    return state;
-  }
-  const header: TurnHeaderItem = {
-    kind: "turn_header",
-    id: `turn_${startedAt.getTime()}_${state.length.toString(36)}`,
-    timestamp: startedAt,
-    startedAt,
-    source: "live",
-  };
-  return [...state, header];
+export interface TurnTiming {
+  startedAt: Date;
+  completedAt: Date;
+  durationMs: number;
 }
 
-export function completeLastTurnHeader(
-  state: StreamItem[],
-  completedAt: Date,
-  outcome: TurnHeaderOutcome,
-): StreamItem[] {
-  for (let i = state.length - 1; i >= 0; i -= 1) {
-    const item = state[i];
-    if (item?.kind !== "turn_header") {
-      continue;
-    }
-    if (item.completedAt !== undefined) {
-      return state;
-    }
-    const updated: TurnHeaderItem = {
-      ...item,
-      completedAt,
-      durationMs: Math.max(0, completedAt.getTime() - item.startedAt.getTime()),
-      outcome,
-    };
-    const next = [...state];
-    next[i] = updated;
-    return next;
-  }
-  return state;
+export interface StreamTurnTiming {
+  byAssistantId: Map<string, TurnTiming>;
+  runningStartedAt: Date | null;
 }
 
-export function synthesizeMissingTurnHeaders(state: StreamItem[]): StreamItem[] {
-  const result: StreamItem[] = [];
-  let segment: StreamItem[] = [];
-  let needsHeader = true;
+export function deriveStreamTurnTiming(params: {
+  agentStatus: string;
+  tail: StreamItem[];
+  head: StreamItem[];
+}): StreamTurnTiming {
+  const byAssistantId = new Map<string, TurnTiming>();
+  let currentUserAt: Date | null = null;
+  let currentLastItemAt: Date | null = null;
+  let currentAssistantIds: string[] = [];
 
-  function flushSegment() {
-    if (segment.length === 0) {
+  const flushCompletedTurn = () => {
+    if (!currentUserAt || !currentLastItemAt || currentAssistantIds.length === 0) {
       return;
     }
-    if (needsHeader) {
-      const first = segment[0];
-      const last = segment[segment.length - 1];
-      const startedAt = first.timestamp;
-      const completedAt = last.timestamp;
-      const header: TurnHeaderItem = {
-        kind: "turn_header",
-        id: `turn_derived_${startedAt.getTime()}_${result.length.toString(36)}`,
-        timestamp: startedAt,
-        startedAt,
-        completedAt,
-        durationMs: Math.max(0, completedAt.getTime() - startedAt.getTime()),
-        outcome: "completed",
-        source: "derived",
-      };
-      result.push(header);
+    const timing: TurnTiming = {
+      startedAt: currentUserAt,
+      completedAt: currentLastItemAt,
+      durationMs: Math.max(0, currentLastItemAt.getTime() - currentUserAt.getTime()),
+    };
+    for (const id of currentAssistantIds) {
+      byAssistantId.set(id, timing);
     }
-    result.push(...segment);
-    segment = [];
-  }
+  };
 
-  for (const item of state) {
+  const visitItem = (item: StreamItem) => {
     if (item.kind === "user_message") {
-      flushSegment();
-      needsHeader = true;
-      result.push(item);
-      continue;
+      flushCompletedTurn();
+      currentUserAt = item.timestamp;
+      currentLastItemAt = null;
+      currentAssistantIds = [];
+      return;
     }
-    if (item.kind === "turn_header") {
-      flushSegment();
-      needsHeader = false;
-      result.push(item);
-      continue;
+    if (!currentUserAt) {
+      return;
     }
-    segment.push(item);
+    currentLastItemAt = item.timestamp;
+    if (item.kind === "assistant_message") {
+      currentAssistantIds.push(item.id);
+    }
+  };
+
+  for (const item of params.tail) {
+    visitItem(item);
+  }
+  for (const item of params.head) {
+    visitItem(item);
   }
 
-  flushSegment();
-  return result;
-}
-
-export function findInFlightTurnStartedAt(params: {
-  agentStatus: string;
-  liveHead: StreamItem[];
-  tail: StreamItem[];
-}): Date | null {
+  const runningStartedAt =
+    params.agentStatus === "running"
+      ? (findLastUserMessageTimestamp(params.head) ?? currentUserAt)
+      : null;
   if (params.agentStatus !== "running") {
-    return null;
+    flushCompletedTurn();
   }
-  const headStartedAt = findLastOpenTurnHeader(params.liveHead)?.startedAt;
-  if (headStartedAt) {
-    return headStartedAt;
-  }
-  return findLastOpenTurnHeader(params.tail)?.startedAt ?? null;
+
+  return {
+    byAssistantId,
+    runningStartedAt,
+  };
 }
 
-export interface TurnHeaderNeighborResolver {
-  getNeighborIndex(index: number, relation: "above" | "below"): number;
-}
-
-export function findTurnHeaderForAssistantTurn(params: {
-  strategy: TurnHeaderNeighborResolver;
-  items: StreamItem[];
-  startIndex: number;
-}): TurnHeaderItem | null {
-  let index = params.startIndex;
-  while (index >= 0 && index < params.items.length) {
-    const item = params.items[index];
-    if (!item) return null;
-    if (item.kind === "turn_header") return item;
-    if (item.kind === "user_message") return null;
-    index = params.strategy.getNeighborIndex(index, "above");
-  }
-  return null;
-}
-
-function findLastTurnHeader(state: StreamItem[]): TurnHeaderItem | null {
-  for (let i = state.length - 1; i >= 0; i -= 1) {
-    const item = state[i];
-    if (item?.kind === "turn_header") {
-      return item;
-    }
-  }
-  return null;
-}
-
-function findLastOpenTurnHeader(state: StreamItem[]): TurnHeaderItem | null {
-  for (let i = state.length - 1; i >= 0; i -= 1) {
-    const item = state[i];
-    if (item?.kind === "turn_header" && item.completedAt === undefined) {
-      return item;
+function findLastUserMessageTimestamp(items: StreamItem[]): Date | null {
+  for (let i = items.length - 1; i >= 0; i -= 1) {
+    const item = items[i];
+    if (item?.kind === "user_message") {
+      return item.timestamp;
     }
   }
   return null;

packages/app/src/types/stream.test.ts

@@ -841,8 +841,8 @@ describe("stream reducer canonical tool calls", () => {
   });
 });
 
-describe("turn headers", () => {
-  it("inserts a live header on turn_started and closes it on turn_completed", () => {
+describe("turn lifecycle events", () => {
+  it("finalizes active stream items without adding timeline rows", () => {
     const startedAt = new Date("2025-01-01T12:00:00Z");
     const completedAt = new Date("2025-01-01T12:00:05Z");
 
@@ -854,16 +854,13 @@ describe("turn headers", () => {
     );
     state = reduceStreamUpdate(state, { type: "turn_completed", provider: "claude" }, completedAt);
 
-    const header = state.find((item) => item.kind === "turn_header");
-    invariant(header?.kind === "turn_header");
-    assert.strictEqual(header.source, "live");
-    assert.strictEqual(header.outcome, "completed");
-    assert.strictEqual(header.durationMs, 5_000);
-    assert.strictEqual(header.startedAt.getTime(), startedAt.getTime());
-    assert.strictEqual(header.completedAt?.getTime(), completedAt.getTime());
+    assert.deepStrictEqual(
+      state.map((item) => item.kind),
+      ["assistant_message"],
+    );
   });
 
-  it("synthesizes a derived header during hydration when turn events are missing", () => {
+  it("hydrates canonical timeline rows without synthetic turn rows", () => {
     const state = hydrateStreamState([
       {
         event: {
@@ -883,24 +880,13 @@ describe("turn headers", () => {
       },
     ]);
 
-    const headers = state.filter((item) => item.kind === "turn_header");
-    assert.strictEqual(headers.length, 1);
-    const [header] = headers;
-    invariant(header?.kind === "turn_header");
-    assert.strictEqual(header.source, "derived");
-    assert.strictEqual(header.outcome, "completed");
-    assert.strictEqual(header.durationMs, 3_000);
-    // Header should sit between the user message and the first assistant item.
-    const kinds = state.map((item) => item.kind);
-    assert.deepStrictEqual(kinds, [
-      "user_message",
-      "turn_header",
-      "assistant_message",
-      "assistant_message",
-    ]);
+    assert.deepStrictEqual(
+      state.map((item) => item.kind),
+      ["user_message", "assistant_message", "assistant_message"],
+    );
   });
 
-  it("does not synthesize a derived header when a live header is already present", () => {
+  it("does not materialize turn_started events during hydration", () => {
     const startedAt = new Date("2025-01-01T14:00:00Z");
     const state = hydrateStreamState([
       {
@@ -918,15 +904,13 @@ describe("turn headers", () => {
       },
     ]);
 
-    const headers = state.filter((item) => item.kind === "turn_header");
-    assert.strictEqual(headers.length, 1);
-    const header = headers[0];
-    invariant(header?.kind === "turn_header");
-    assert.strictEqual(header.source, "live");
-    assert.strictEqual(header.completedAt, undefined);
+    assert.deepStrictEqual(
+      state.map((item) => item.kind),
+      ["user_message", "assistant_message"],
+    );
   });
 
-  it("skips synthesis for turns with no assistant output", () => {
+  it("keeps adjacent user messages as adjacent timeline rows", () => {
     const state = hydrateStreamState([
       {
         event: {
@@ -946,7 +930,9 @@ describe("turn headers", () => {
       },
     ]);
 
-    const headers = state.filter((item) => item.kind === "turn_header");
-    assert.strictEqual(headers.length, 0);
+    assert.deepStrictEqual(
+      state.map((item) => item.kind),
+      ["user_message", "user_message"],
+    );
   });
 });

packages/app/src/types/stream.ts

@@ -3,11 +3,6 @@ import type { AgentAttachment, AgentStreamEventPayload } from "@server/shared/me
 import type { AttachmentMetadata } from "@/attachments/types";
 import { extractTaskEntriesFromToolCall } from "../utils/tool-call-parsers";
 import { splitMarkdownBlocks } from "@/utils/split-markdown-blocks";
-import {
-  appendLiveTurnHeader,
-  completeLastTurnHeader,
-  synthesizeMissingTurnHeaders,
-} from "@/timeline/turn-time";
 
 /**
  * Simple hash function for deterministic ID generation
@@ -55,21 +50,7 @@ export type StreamItem =
   | ToolCallItem
   | TodoListItem
   | ActivityLogItem
-  | CompactionItem
-  | TurnHeaderItem;
-
-export type TurnHeaderOutcome = "completed" | "failed" | "canceled";
-
-export interface TurnHeaderItem {
-  kind: "turn_header";
-  id: string;
-  timestamp: Date;
-  startedAt: Date;
-  completedAt?: Date;
-  durationMs?: number;
-  outcome?: TurnHeaderOutcome;
-  source: "live" | "derived";
-}
+  | CompactionItem;
 
 export type UserMessageImageAttachment = AttachmentMetadata;
 
@@ -723,15 +704,10 @@ export function reduceStreamUpdate(
     case "timeline":
       return reduceTimelineEvent(state, event, timestamp, source);
     case "thread_started":
-      return finalizeActiveThoughts(state);
     case "turn_started":
-      return appendLiveTurnHeader(finalizeActiveThoughts(state), timestamp);
     case "turn_completed":
-      return completeLastTurnHeader(finalizeActiveThoughts(state), timestamp, "completed");
     case "turn_failed":
-      return completeLastTurnHeader(finalizeActiveThoughts(state), timestamp, "failed");
     case "turn_canceled":
-      return completeLastTurnHeader(finalizeActiveThoughts(state), timestamp, "canceled");
     case "permission_requested":
     case "permission_resolved":
     case "attention_required":
@@ -755,7 +731,7 @@ export function hydrateStreamState(
     return reduceStreamUpdate(state, event, timestamp, options);
   }, []);
 
-  return synthesizeMissingTurnHeaders(finalizeActiveThoughts(hydrated));
+  return finalizeActiveThoughts(hydrated);
 }
 
 /**

packages/server/src/server/agent/providers/codex-app-server-agent.test.ts

@@ -1418,6 +1418,68 @@ describe("Codex app-server provider", () => {
     ]);
   });
 
+  test("uses Codex turn timestamps for timestamp-less persisted history items", async () => {
+    const session = createSession();
+    session.client = {
+      request: vi.fn(async (method: string) => {
+        if (method !== "thread/read") {
+          return {};
+        }
+        return {
+          thread: {
+            turns: [
+              {
+                startedAt: 1_778_832_941,
+                completedAt: 1_778_833_094,
+                items: [
+                  {
+                    type: "userMessage",
+                    id: "user-history",
+                    content: [{ type: "text", text: "Check OpenCode timestamps." }],
+                  },
+                  {
+                    type: "agentMessage",
+                    id: "message-history",
+                    text: "History loaded.",
+                  },
+                ],
+              },
+            ],
+          },
+        };
+      }),
+    };
+
+    await asInternals(session).loadPersistedHistory();
+
+    const history: AgentStreamEvent[] = [];
+    for await (const event of session.streamHistory()) {
+      history.push(event);
+    }
+
+    expect(history).toEqual([
+      {
+        type: "timeline",
+        provider: "codex",
+        timestamp: "2026-05-15T08:15:41.000Z",
+        item: {
+          type: "user_message",
+          text: "Check OpenCode timestamps.",
+        },
+      },
+      {
+        type: "timeline",
+        provider: "codex",
+        timestamp: "2026-05-15T08:18:14.000Z",
+        item: {
+          type: "assistant_message",
+          text: "History loaded.",
+          messageId: "message-history",
+        },
+      },
+    ]);
+  });
+
   test("preserves Codex app-server assistant item ids in persisted history", async () => {
     const session = createSession();
     session.client = {

packages/server/src/server/agent/providers/codex-app-server-agent.ts

@@ -1462,6 +1462,28 @@ function readCodexHistoryTimestamp(item: unknown): string | null {
   );
 }
 
+function readCodexTurnHistoryTimestamp(
+  turn: unknown,
+  timelineItem: AgentTimelineItem,
+): string | null {
+  const record = toObjectRecord(turn);
+  if (!record) {
+    return null;
+  }
+
+  const startedAt =
+    normalizeProviderReplayTimestamp(record.startedAt) ??
+    normalizeProviderReplayTimestamp(record.started_at);
+  const completedAt =
+    normalizeProviderReplayTimestamp(record.completedAt) ??
+    normalizeProviderReplayTimestamp(record.completed_at);
+
+  if (timelineItem.type === "user_message") {
+    return startedAt ?? completedAt;
+  }
+  return completedAt ?? startedAt;
+}
+
 function codexImageOutputFromResult(result: unknown): ProviderImageOutput | null {
   if (typeof result === "string") {
     const trimmed = result.trim();
@@ -1616,7 +1638,8 @@ async function loadCodexThreadHistoryTimeline(params: {
     for (const item of turn.items) {
       const timelineItem = threadItemToTimeline(item, { cwd: params.cwd });
       if (timelineItem) {
-        const timestamp = readCodexHistoryTimestamp(item);
+        const timestamp =
+          readCodexHistoryTimestamp(item) ?? readCodexTurnHistoryTimestamp(turn, timelineItem);
         timeline.push({
           item: timelineItem,
           timestamp: timestamp ?? undefined,