Polish issue chat layout and add UX lab

Co-Authored-By: Paperclip <noreply@paperclip.ing>

ui/src/components/IssueChatThread.test.tsx

@@ -0,0 +1,123 @@
+// @vitest-environment jsdom
+
+import { act } from "react";
+import type { ReactNode } from "react";
+import { createRoot } from "react-dom/client";
+import { MemoryRouter } from "react-router-dom";
+import { afterEach, beforeEach, describe, expect, it, vi } from "vitest";
+import { IssueChatThread } from "./IssueChatThread";
+
+vi.mock("@assistant-ui/react", () => ({
+  AssistantRuntimeProvider: ({ children }: { children: ReactNode }) => <div>{children}</div>,
+  ThreadPrimitive: {
+    Root: ({ children, className }: { children: ReactNode; className?: string }) => (
+      <div data-testid="thread-root" className={className}>{children}</div>
+    ),
+    Viewport: ({ children, className }: { children: ReactNode; className?: string }) => (
+      <div data-testid="thread-viewport" className={className}>{children}</div>
+    ),
+    Empty: ({ children }: { children: ReactNode }) => <div>{children}</div>,
+    Messages: () => <div data-testid="thread-messages" />,
+  },
+  MessagePrimitive: {
+    Root: ({ children }: { children: ReactNode }) => <div>{children}</div>,
+    Content: () => null,
+  },
+  useAui: () => ({ thread: () => ({ append: vi.fn() }) }),
+  useAuiState: () => false,
+  useMessage: () => ({
+    id: "message",
+    role: "assistant",
+    createdAt: new Date("2026-04-06T12:00:00.000Z"),
+    content: [],
+    metadata: { custom: {} },
+    status: { type: "complete" },
+  }),
+}));
+
+vi.mock("./transcript/useLiveRunTranscripts", () => ({
+  useLiveRunTranscripts: () => ({
+    transcriptByRun: new Map(),
+    hasOutputForRun: () => false,
+  }),
+}));
+
+vi.mock("./MarkdownBody", () => ({
+  MarkdownBody: ({ children }: { children: ReactNode }) => <div>{children}</div>,
+}));
+
+vi.mock("./MarkdownEditor", () => ({
+  MarkdownEditor: () => <textarea aria-label="Issue chat editor" />,
+}));
+
+vi.mock("./InlineEntitySelector", () => ({
+  InlineEntitySelector: () => null,
+}));
+
+vi.mock("./Identity", () => ({
+  Identity: ({ name }: { name: string }) => <span>{name}</span>,
+}));
+
+vi.mock("./OutputFeedbackButtons", () => ({
+  OutputFeedbackButtons: () => null,
+}));
+
+vi.mock("./AgentIconPicker", () => ({
+  AgentIcon: () => null,
+}));
+
+vi.mock("./StatusBadge", () => ({
+  StatusBadge: ({ status }: { status: string }) => <span>{status}</span>,
+}));
+
+vi.mock("../hooks/usePaperclipIssueRuntime", () => ({
+  usePaperclipIssueRuntime: () => ({}),
+}));
+
+// eslint-disable-next-line @typescript-eslint/no-explicit-any
+(globalThis as any).IS_REACT_ACT_ENVIRONMENT = true;
+
+describe("IssueChatThread", () => {
+  let container: HTMLDivElement;
+
+  beforeEach(() => {
+    container = document.createElement("div");
+    document.body.appendChild(container);
+  });
+
+  afterEach(() => {
+    container.remove();
+  });
+
+  it("drops the count heading and does not use an internal scrollbox", () => {
+    const root = createRoot(container);
+
+    act(() => {
+      root.render(
+        <MemoryRouter>
+          <IssueChatThread
+            comments={[]}
+            linkedRuns={[]}
+            timelineEvents={[]}
+            liveRuns={[]}
+            onAdd={async () => {}}
+            showComposer={false}
+            enableLiveTranscriptPolling={false}
+          />
+        </MemoryRouter>,
+      );
+    });
+
+    expect(container.textContent).toContain("Jump to latest");
+    expect(container.textContent).not.toContain("Chat (");
+
+    const viewport = container.querySelector('[data-testid="thread-viewport"]') as HTMLDivElement | null;
+    expect(viewport).not.toBeNull();
+    expect(viewport?.className).not.toContain("overflow-y-auto");
+    expect(viewport?.className).not.toContain("max-h-[70vh]");
+
+    act(() => {
+      root.unmount();
+    });
+  });
+});