diff --git a/packages/tui/test/alt-screen-large-transcript-bench.ts b/packages/tui/test/alt-screen-large-transcript-bench.ts
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+++ b/packages/tui/test/alt-screen-large-transcript-bench.ts
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+/**
+ * Alternate-screen large-transcript benchmark.
+ *
+ * Mirrors the fullscreen transcript shape used by the coding agent:
+ *
+ * ScrollView
+ * └── document Container
+ *     ├── header Container
+ *     ├── resources Container
+ *     └── chat Container
+ *         └── 2,500 alternating user/assistant Markdown components
+ *
+ * Measures warm steady frames, one-line scrolling, streaming updates to the
+ * final assistant message, and width changes that invalidate Markdown caches.
+ *
+ * Run from the repository root:
+ *   node --experimental-strip-types packages/tui/test/alt-screen-large-transcript-bench.ts
+ */
+
+import { performance } from "node:perf_hooks";
+import { Markdown, type MarkdownTheme } from "../src/components/markdown.ts";
+import { ScrollView } from "../src/components/scroll-view.ts";
+import { Text } from "../src/components/text.ts";
+import { VStack } from "../src/components/v-stack.ts";
+import type { Terminal } from "../src/terminal.ts";
+import { Container } from "../src/tui.ts";
+import { TuiAltScreen } from "../src/tui-alt-screen.ts";
+
+const COLUMNS = 80;
+const ROWS = 50;
+const COMPONENT_COUNT = 2_500;
+const WARMUP_FRAMES = 20;
+
+const theme: MarkdownTheme = {
+	heading: (text) => text,
+	link: (text) => text,
+	linkUrl: (text) => text,
+	code: (text) => text,
+	codeBlock: (text) => text,
+	codeBlockBorder: (text) => text,
+	quote: (text) => text,
+	quoteBorder: (text) => text,
+	hr: (text) => text,
+	listBullet: (text) => text,
+	bold: (text) => text,
+	italic: (text) => text,
+	strikethrough: (text) => text,
+	underline: (text) => text,
+};
+
+class NullTerminal implements Terminal {
+	columns = COLUMNS;
+	rows = ROWS;
+
+	start(_onInput: (data: string) => void, _onResize: () => void): void {}
+	stop(): void {}
+	async drainInput(): Promise<void> {}
+	write(_data: string): void {}
+	get kittyProtocolActive(): boolean {
+		return false;
+	}
+	moveBy(_lines: number): void {}
+	hideCursor(): void {}
+	showCursor(): void {}
+	clearLine(): void {}
+	clearFromCursor(): void {}
+	clearScreen(): void {}
+	setTitle(_title: string): void {}
+	setProgress(_active: boolean): void {}
+}
+
+const userMarkdown = [
+	"## User request",
+	"",
+	"Please inspect this implementation carefully and report the relevant behavior.",
+	"",
+	"- preserve correctness",
+	"- include concrete evidence",
+].join("\n");
+
+const assistantMarkdown = [
+	"## Analysis",
+	"",
+	"This response contains representative prose with **inline styles**, a [link](https://example.com), and enough words to wrap across terminal rows at realistic widths. The implementation should preserve all observable behavior while avoiding unnecessary allocation.",
+	"",
+	"1. First item with explanatory text and a concrete example.",
+	"2. Second item with more explanatory text and another example.",
+	"3. Third item that ensures list rendering is represented.",
+	"",
+	"```ts",
+	"function render(width: number): string[] {",
+	"  const lines: string[] = [];",
+	"  for (const child of children) {",
+	"    const childLines = child.render(width);",
+	"    for (const line of childLines) lines.push(line);",
+	"  }",
+	"  const height = lines.length;",
+	"  const start = Math.max(0, from);",
+	"  const end = Math.min(height, start + count);",
+	"  const visible = lines.slice(start, end);",
+	"  updateLayout(height, viewportHeight);",
+	"  return visible;",
+	"}",
+	"```",
+	"",
+	"> A quoted conclusion with enough text to exercise wrapping and inline rendering in the real Markdown component.",
+	"",
+	"Final paragraph with a concise recommendation and a note about correctness tests.",
+].join("\n");
+
+const header = new Container();
+header.addChild(new Text("pi benchmark\nheader line", 0, 0));
+const resources = new Container();
+resources.addChild(new Text("resource", 0, 0));
+const chat = new Container();
+let streamingMarkdown: Markdown | undefined;
+for (let index = 0; index < COMPONENT_COUNT; index++) {
+	const markdown = new Markdown(index % 2 === 0 ? userMarkdown : assistantMarkdown, 1, 0, theme);
+	chat.addChild(markdown);
+	if (index === COMPONENT_COUNT - 1) streamingMarkdown = markdown;
+}
+if (!streamingMarkdown) throw new Error("Benchmark requires at least one assistant Markdown component");
+
+const document = new Container();
+document.addChild(header);
+document.addChild(resources);
+document.addChild(chat);
+
+const transcript = new ScrollView(document, { follow: "none", primary: true });
+const dock = new VStack([new Text("editor\nfooter", 0, 0)]);
+const root = new VStack([
+	{ component: transcript, basis: 0, grow: 1, minSize: 1 },
+	{ component: dock, basis: "auto", minSize: 1 },
+]);
+const terminal = new NullTerminal();
+const tui = new TuiAltScreen(terminal, false, "/tmp/pi-tui-bench");
+tui.setLayoutRoot(root);
+tui.start();
+tui.renderNow();
+
+const totalLines = document.render(terminal.columns).length;
+transcript.scrollTo(Math.floor(totalLines / 2));
+for (let frame = 0; frame < WARMUP_FRAMES; frame++) tui.renderNow();
+
+function measure(name: string, frames: number, beforeFrame: (frame: number) => void): void {
+	const start = performance.now();
+	for (let frame = 0; frame < frames; frame++) {
+		beforeFrame(frame);
+		tui.renderNow();
+	}
+	const millisecondsPerFrame = (performance.now() - start) / frames;
+	console.log(`${name}: ${millisecondsPerFrame.toFixed(3)} ms/frame (${frames} frames)`);
+}
+
+console.log(`components=${COMPONENT_COUNT} lines=${totalLines} viewport=${terminal.columns}x${terminal.rows}`);
+measure("steady", 200, () => {});
+transcript.scrollTo(Math.floor(totalLines / 2));
+measure("scroll", 200, () => transcript.scrollBy(1));
+measure("streaming", 100, (frame) => {
+	streamingMarkdown.setText(`${assistantMarkdown}\n\nstream ${"x".repeat(frame + 1)}`);
+});
+measure("resize", 10, (frame) => {
+	terminal.columns = frame % 2 === 0 ? COLUMNS - 1 : COLUMNS;
+});
+
+tui.stop();