Reduce chat timeline work-row rerenders

apps/web/src/components/ChatView.tsx

@@ -4729,7 +4729,6 @@ function ChatViewContent(props: ChatViewProps) {
               <MessagesTimeline
                 key={activeThread.id}
                 isWorking={isWorking}
-                activeTurnInProgress={isWorking || !latestTurnSettled}
                 activeTurnStartedAt={activeWorkStartedAt}
                 listRef={legendListRef}
                 timelineEntries={timelineEntries}

apps/web/src/components/chat/MessagesTimeline.logic.test.ts

@@ -879,6 +879,69 @@ describe("deriveMessagesTimelineRows", () => {
     expect(assistantRow?.showAssistantMeta).toBe(false);
     expect(assistantRow?.showAssistantCopyButton).toBe(false);
   });
+
+  it("marks only the unsettled turn work row as in progress", () => {
+    const rows = deriveMessagesTimelineRows({
+      timelineEntries: [
+        {
+          id: "old-work-entry",
+          kind: "work",
+          createdAt: "2026-01-01T00:00:08Z",
+          entry: {
+            id: "old-work",
+            createdAt: "2026-01-01T00:00:08Z",
+            turnId: "turn-1" as never,
+            label: "Read files",
+            tone: "tool" as const,
+          },
+        },
+        {
+          id: "user-entry",
+          kind: "message",
+          createdAt: "2026-01-01T00:00:12Z",
+          message: {
+            id: "user-message" as never,
+            role: "user",
+            text: "Continue",
+            turnId: null,
+            createdAt: "2026-01-01T00:00:12Z",
+            updatedAt: "2026-01-01T00:00:12Z",
+            streaming: false,
+          },
+        },
+        {
+          id: "active-work-entry",
+          kind: "work",
+          createdAt: "2026-01-01T00:00:18Z",
+          entry: {
+            id: "active-work",
+            createdAt: "2026-01-01T00:00:18Z",
+            turnId: "turn-2" as never,
+            label: "Run tests",
+            tone: "tool" as const,
+          },
+        },
+      ],
+      latestTurn: {
+        turnId: "turn-2" as never,
+        state: "running",
+        startedAt: "2026-01-01T00:00:16Z",
+        completedAt: null,
+      },
+      expandedTurnIds: new Set(["turn-1" as never]),
+      isWorking: false,
+      activeTurnStartedAt: null,
+      turnDiffSummaryByAssistantMessageId: new Map(),
+      revertTurnCountByUserMessageId: new Map(),
+    });
+
+    const workRows = rows.filter((row) => row.kind === "work");
+
+    expect(workRows.map((row) => [row.id, row.turnInProgress])).toEqual([
+      ["old-work-entry", false],
+      ["active-work-entry", true],
+    ]);
+  });
 });
 
 describe("computeStableMessagesTimelineRows", () => {
@@ -987,6 +1050,92 @@ describe("computeStableMessagesTimelineRows", () => {
     expect(repeated.result[0]).toBe(initial.result[0]);
   });
 
+  it("reuses settled work rows when a different turn stops running", () => {
+    const timelineEntries = [
+      {
+        id: "old-work-entry",
+        kind: "work" as const,
+        createdAt: "2026-01-01T00:00:08Z",
+        entry: {
+          id: "old-work",
+          createdAt: "2026-01-01T00:00:08Z",
+          turnId: "turn-1" as never,
+          label: "Read files",
+          tone: "tool" as const,
+        },
+      },
+      {
+        id: "user-entry",
+        kind: "message" as const,
+        createdAt: "2026-01-01T00:00:12Z",
+        message: {
+          id: "user-message" as never,
+          role: "user" as const,
+          text: "Continue",
+          turnId: null,
+          createdAt: "2026-01-01T00:00:12Z",
+          updatedAt: "2026-01-01T00:00:12Z",
+          streaming: false,
+        },
+      },
+      {
+        id: "active-work-entry",
+        kind: "work" as const,
+        createdAt: "2026-01-01T00:00:18Z",
+        entry: {
+          id: "active-work",
+          createdAt: "2026-01-01T00:00:18Z",
+          turnId: "turn-2" as never,
+          label: "Run tests",
+          tone: "tool" as const,
+        },
+      },
+    ];
+
+    const runningRows = deriveMessagesTimelineRows({
+      timelineEntries,
+      latestTurn: {
+        turnId: "turn-2" as never,
+        state: "running",
+        startedAt: "2026-01-01T00:00:16Z",
+        completedAt: null,
+      },
+      expandedTurnIds: new Set(["turn-1" as never, "turn-2" as never]),
+      isWorking: false,
+      activeTurnStartedAt: null,
+      turnDiffSummaryByAssistantMessageId: new Map(),
+      revertTurnCountByUserMessageId: new Map(),
+    });
+    const initial = computeStableMessagesTimelineRows(runningRows, {
+      byId: new Map(),
+      result: [],
+    });
+
+    const settledRows = deriveMessagesTimelineRows({
+      timelineEntries,
+      latestTurn: {
+        turnId: "turn-2" as never,
+        state: "completed",
+        startedAt: "2026-01-01T00:00:16Z",
+        completedAt: "2026-01-01T00:00:30Z",
+      },
+      expandedTurnIds: new Set(["turn-1" as never, "turn-2" as never]),
+      isWorking: false,
+      activeTurnStartedAt: null,
+      turnDiffSummaryByAssistantMessageId: new Map(),
+      revertTurnCountByUserMessageId: new Map(),
+    });
+
+    const repeated = computeStableMessagesTimelineRows(settledRows, initial);
+
+    expect(repeated.result.find((row) => row.id === "old-work-entry")).toBe(
+      initial.result.find((row) => row.id === "old-work-entry"),
+    );
+    expect(repeated.result.find((row) => row.id === "active-work-entry")).not.toBe(
+      initial.result.find((row) => row.id === "active-work-entry"),
+    );
+  });
+
   it("returns a new result when row order changes without content changes", () => {
     const firstUserMessage = {
       id: "user-1" as never,

apps/web/src/components/chat/MessagesTimeline.logic.ts

@@ -41,6 +41,7 @@ export type MessagesTimelineRow =
       id: string;
       createdAt: string;
       groupedEntries: WorkLogEntry[];
+      turnInProgress: boolean;
     }
   | {
       kind: "turn-fold";
@@ -361,6 +362,9 @@ export function deriveMessagesTimelineRows(input: {
         id: timelineEntry.id,
         createdAt: timelineEntry.createdAt,
         groupedEntries,
+        turnInProgress:
+          unsettledTurnId !== null &&
+          groupedEntries.some((entry) => entry.turnId === unsettledTurnId),
       });
       index = cursor - 1;
       continue;
@@ -460,7 +464,10 @@ function isRowUnchanged(a: MessagesTimelineRow, b: MessagesTimelineRow): boolean
       return a.proposedPlan === (b as typeof a).proposedPlan;
 
     case "work":
-      return Equal.equals(a.groupedEntries, (b as typeof a).groupedEntries);
+      return (
+        a.turnInProgress === (b as typeof a).turnInProgress &&
+        Equal.equals(a.groupedEntries, (b as typeof a).groupedEntries)
+      );
 
     case "message": {
       const bm = b as typeof a;

apps/web/src/components/chat/MessagesTimeline.test.tsx

@@ -93,7 +93,6 @@ const MESSAGE_CREATED_AT = "2026-03-17T19:12:28.000Z";
 function buildProps() {
   return {
     isWorking: false,
-    activeTurnInProgress: false,
     activeTurnStartedAt: null,
     listRef: createRef<LegendListRef | null>(),
     latestTurn: null,