Refine tool call summaries and scrolling (#2069)

* feat(app): refine tool call summaries and scrolling

Keep summary groups stable from the first tool call, preserve live activity feedback, and scroll expanded groups to the latest entry. Consolidate web scrollbar styling around the native browser mechanism.

* refactor(app): reuse tool call height constant

* fix(app): preserve tool call summary state

* fix(app): refresh web tool groups on expand

* fix(app): preserve grouped tool errors

packages/app/src/agent-stream/strategy-web.test.tsx

@@ -6,7 +6,7 @@ import { act } from "react";
 import { createRoot, type Root } from "react-dom/client";
 import { afterEach, beforeEach, describe, expect, it, vi } from "vitest";
 import type { StreamItem } from "@/types/stream";
-import type { StreamSegmentRenderers, StreamViewportHandle } from "./strategy";
+import type { StreamRenderInput, StreamSegmentRenderers, StreamViewportHandle } from "./strategy";
 import { createWebStreamStrategy } from "./strategy-web";
 
 vi.hoisted(() => {
@@ -25,8 +25,6 @@ vi.hoisted(() => {
   });
 });
 
-vi.mock("@/components/use-web-scrollbar", () => ({ useWebElementScrollbar: () => null }));
-
 function userMessage(index: number): StreamItem {
   return {
     kind: "user_message",
@@ -148,6 +146,59 @@ describe("createWebStreamStrategy", () => {
     expect(rowRenderCount.mock.calls.length).toBeLessThanOrEqual(historyVirtualized.length);
   });
 
+  it("rerenders a stable live-head row when its revision changes", () => {
+    const strategy = createWebStreamStrategy({ isMobileBreakpoint: false });
+    const viewportRef = React.createRef<StreamViewportHandle>();
+    const liveHead = [userMessage(1)];
+    let label = "collapsed";
+    const renderLiveHeadRow = vi.fn(() => <div>{label}</div>);
+    const renderInput: StreamRenderInput = {
+      agentId: "agent",
+      segments: {
+        historyVirtualized: [],
+        historyMounted: [],
+        liveHead,
+      },
+      boundary: {
+        hasVirtualizedHistory: false,
+        hasMountedHistory: false,
+        hasLiveHead: true,
+      },
+      renderers: {
+        ...createRenderers(vi.fn()),
+        renderLiveHeadRow,
+      },
+      listEmptyComponent: null,
+      viewportRef,
+      routeBottomAnchorRequest: null,
+      isAuthoritativeHistoryReady: true,
+      onNearBottomChange: vi.fn(),
+      onNearHistoryStart: vi.fn(),
+      isLoadingOlderHistory: false,
+      hasOlderHistory: false,
+      scrollEnabled: true,
+      listStyle: null,
+      baseListContentContainerStyle: null,
+      forwardListContentContainerStyle: null,
+    };
+    container = document.createElement("div");
+    document.body.appendChild(container);
+    root = createRoot(container);
+
+    act(() => {
+      root?.render(strategy.render({ ...renderInput, liveHeadRowRevision: 0 }));
+    });
+    expect(container.textContent).toContain("collapsed");
+
+    label = "expanded";
+    act(() => {
+      root?.render(strategy.render({ ...renderInput, liveHeadRowRevision: 1 }));
+    });
+
+    expect(container.textContent).toContain("expanded");
+    expect(renderLiveHeadRow).toHaveBeenCalledTimes(2);
+  });
+
   it("fires near-history-start when the user scrolls near the top", async () => {
     const strategy = createWebStreamStrategy({ isMobileBreakpoint: true });
     const viewportRef = React.createRef<StreamViewportHandle>();