oh-my-pi/packages/coding-agent/test/tool-live-region-scrollback.test.ts

import { beforeAll, describe, expect, it } from "bun:test";
import type { AssistantMessage } from "@oh-my-pi/pi-ai";
import { Settings } from "@oh-my-pi/pi-coding-agent/config/settings";
import { AssistantMessageComponent } from "@oh-my-pi/pi-coding-agent/modes/components/assistant-message";
import { ToolExecutionComponent } from "@oh-my-pi/pi-coding-agent/modes/components/tool-execution";
import { TranscriptContainer } from "@oh-my-pi/pi-coding-agent/modes/components/transcript-container";
import { initTheme } from "@oh-my-pi/pi-coding-agent/modes/theme/theme";
import { type Component, Text, TUI } from "@oh-my-pi/pi-tui";
import { VirtualTerminal } from "../../tui/test/virtual-terminal";

class MutableLiveBlock implements Component {
	#lines: string[];
	#finalized: boolean;

	constructor(lines: string[], finalized = false) {
		this.#lines = [...lines];
		this.#finalized = finalized;
	}

	render(width: number): string[] {
		return this.#lines.map(line => line.slice(0, width));
	}

	setLines(lines: string[]): void {
		this.#lines = [...lines];
	}

	isTranscriptBlockFinalized(): boolean {
		return this.#finalized;
	}
}

function markerLines(prefix: string, count: number): string[] {
	return Array.from({ length: count }, (_unused, i) => `${prefix}${i}`);
}

function stripRows(rows: string[]): string {
	return rows.map(row => Bun.stripANSI(row).trimEnd()).join("\n");
}

describe("transcript reactive commit boundary", () => {
	it("treats growth before stable trailing chrome as append-only", async () => {
		const chat = new TranscriptContainer();
		const block = new MutableLiveBlock(["top", "stable", "bottom"]);
		chat.addChild(block);

		expect(chat.render(80)).toEqual(["top", "stable", "bottom"]);
		expect(chat.getNativeScrollbackCommitSafeEnd()).toBeUndefined();

		block.setLines(["top", "stable", "inserted", "bottom"]);
		expect(chat.render(80)).toEqual(["top", "stable", "inserted", "bottom"]);
		expect(chat.getNativeScrollbackCommitSafeEnd()).toBe(4);
	});

	it("treats in-place growth of the trailing line as append-only", async () => {
		const chat = new TranscriptContainer();
		// Models a streaming assistant reply: stable head rows plus a current
		// line that grows token-by-token without adding a new row — the dominant
		// streaming shape, and the one a strict line-count-growth check missed,
		// stranding the scrolled-off head outside tmux pane history.
		const block = new MutableLiveBlock(["para one", "para two", "the quick brown"]);
		chat.addChild(block);

		chat.render(80);
		block.setLines(["para one", "para two", "the quick brown fox"]);
		chat.render(80);
		expect(chat.getNativeScrollbackCommitSafeEnd()).toBe(3);
	});

	it("marks interior live re-layout volatile and defers commit", async () => {
		const chat = new TranscriptContainer();
		const block = new MutableLiveBlock(["top", "old", "bottom"]);
		chat.addChild(block);

		chat.render(80);
		block.setLines(["top", "new", "extra", "bottom"]);
		expect(chat.render(80)).toEqual(["top", "new", "extra", "bottom"]);
		expect(chat.getNativeScrollbackCommitSafeEnd()).toBeUndefined();

		block.setLines(["top", "new", "extra", "more", "bottom"]);
		chat.render(80);
		expect(chat.getNativeScrollbackCommitSafeEnd()).toBeUndefined();
	});

	it("treats escape placement and pad drift on visually unchanged rows as append-only", async () => {
		const chat = new TranscriptContainer();
		// Field failure shape (streaming styled thinking): the previous last row
		// carried the span-closing SGR before its width padding; when the
		// paragraph wrapped onto a new row, the close moved to the new last row
		// while the first row's visible cells stayed identical.
		const sty = "\x1b[38;2;156;163;176m";
		const block = new MutableLiveBlock([`${sty}alpha beta\x1b[39m   `]);
		chat.addChild(block);

		chat.render(80);
		block.setLines([`${sty}alpha beta   `, `${sty}gamma\x1b[39m        `]);
		chat.render(80);
		expect(chat.getNativeScrollbackCommitSafeEnd()).toBe(2);
	});

	it("treats a wrap-shrink of the trailing line as append-only", async () => {
		const chat = new TranscriptContainer();
		// A streamed token extends the last word past the wrap column, so the
		// word moves down onto an appended row and the previous bottom line
		// shrinks. The bottom line is on screen by definition, so this is not a
		// rewrite of committed-candidate rows.
		const block = new MutableLiveBlock(["para one", "foo bar baz"]);
		chat.addChild(block);

		chat.render(80);
		block.setLines(["para one", "foo bar", "bazqux and more"]);
		chat.render(80);
		expect(chat.getNativeScrollbackCommitSafeEnd()).toBe(3);
	});

	it("re-earns append-only after a one-off interior rewrite heals", async () => {
		const chat = new TranscriptContainer();
		const block = new MutableLiveBlock(["top", "old", "bottom"]);
		chat.addChild(block);

		chat.render(80);
		// Interior rewrite (a codespan finalizing across a wrap) suspends commits.
		block.setLines(["top", "new", "bottom"]);
		chat.render(80);
		expect(chat.getNativeScrollbackCommitSafeEnd()).toBeUndefined();

		// Clean static frames re-arm the block...
		for (let i = 0; i < 30; i++) chat.render(80);
		// ...and the next append-shaped frame resumes committing the full block,
		// so the pinned emitter can backfill the stalled gap contiguously.
		block.setLines(["top", "new", "bottom", "appended"]);
		chat.render(80);
		expect(chat.getNativeScrollbackCommitSafeEnd()).toBe(4);
	});

	it("keeps a periodically rewriting block (spinner) deferred", async () => {
		const chat = new TranscriptContainer();
		const block = new MutableLiveBlock(["⠋ running", "body"]);
		chat.addChild(block);

		chat.render(80);
		const glyphs = ["⠙", "⠹", "⠸", "⠼", "⠴", "⠦", "⠧", "⠇", "⠏", "⠋"];
		for (const glyph of glyphs) {
			// Spinner advances every third frame; the static frames in between
			// must never accumulate into a re-arm.
			block.setLines([`${glyph} running`, "body"]);
			chat.render(80);
			chat.render(80);
			chat.render(80);
		}
		block.setLines(["⠋ running", "body", "appended"]);
		chat.render(80);
		expect(chat.getNativeScrollbackCommitSafeEnd()).toBeUndefined();
	});

	it("commits the settled head of a block whose tail keeps rewriting (task progress shape)", () => {
		const chat = new TranscriptContainer();
		const head = markerLines("head-", 8);
		const block = new MutableLiveBlock([...head, "⠋ agents running · 0 tools"]);
		chat.addChild(block);
		chat.render(80);

		// The progress tail rewrites every frame, so append-only is never
		// earned — but the head rows stay visibly identical the whole time.
		for (let i = 1; i <= 62; i++) {
			block.setLines([...head, `⠋ agents running · ${i} tools`]);
			chat.render(80);
		}

		// The settled head must become commit-safe; otherwise a tall block's
		// scrolled-off head is neither committed nor on screen for the whole
		// run — the transcript reads as cut off until the tool seals.
		expect(chat.getNativeScrollbackCommitSafeEnd()).toBe(8);
	});

	it("retreats the settled-head boundary when a promoted row is rewritten", () => {
		const chat = new TranscriptContainer();
		const head = markerLines("head-", 8);
		const block = new MutableLiveBlock([...head, "tail-0"]);
		chat.addChild(block);
		chat.render(80);
		for (let i = 1; i <= 62; i++) {
			block.setLines([...head, `tail-${i}`]);
			chat.render(80);
		}
		expect(chat.getNativeScrollbackCommitSafeEnd()).toBe(8);

		// A collapse/re-layout rewrites a promoted row: the boundary retreats
		// to the divergence (the engine audit owns rows already committed).
		block.setLines([...head.slice(0, 3), "rewritten", ...head.slice(4), "tail-x"]);
		chat.render(80);
		expect(chat.getNativeScrollbackCommitSafeEnd()).toBe(3);
	});

	it("stops re-promoting slow-ticking rows after the first promoted-row rewrite", () => {
		const chat = new TranscriptContainer();
		const head = markerLines("head-", 8);
		// Task progress tree shape: per-agent rows whose tool/cost counters tick
		// every few seconds — far slower than the promotion window, so each row
		// looks "settled" between updates. Without the rewrite floor, every
		// quiet stretch re-promotes the tree, every tick rewrites a
		// committed row, and the engine audit recommits — spraying a stale
		// snapshot of the block into scrollback for the whole run.
		const tree = (a: number, b: number, c: number) => [
			`agent-one · ${a} tools`,
			`agent-two · ${b} tools`,
			`agent-three · ${c} tools`,
		];
		const block = new MutableLiveBlock([...head, ...tree(0, 0, 0)]);
		chat.addChild(block);
		chat.render(80);

		// Stagger slow updates with quiet stretches longer than the promotion
		// window. The floor arms the first time an already-promoted row ticks
		// and descends to each promoted ticker as it re-ticks; after the
		// topmost ticker has re-ticked once post-promotion, the boundary must
		// converge to the static head and never reach into the tree again.
		let maxSafeEndAfterConvergence = 0;
		const counters: [number, number, number] = [0, 0, 0];
		for (let tick = 0; tick < 9; tick++) {
			counters[tick % 3] += 1;
			block.setLines([...head, ...tree(...counters)]);
			for (let frame = 0; frame < 40; frame++) {
				chat.render(80);
				const safeEnd = chat.getNativeScrollbackCommitSafeEnd() ?? 0;
				if (tick >= 4) maxSafeEndAfterConvergence = Math.max(maxSafeEndAfterConvergence, safeEnd);
			}
		}

		// The static head still commits; the slow-ticking tree stays deferred.
		expect(chat.getNativeScrollbackCommitSafeEnd()).toBe(8);
		expect(maxSafeEndAfterConvergence).toBe(8);
	});

	it("keeps the rewrite floor anchored across append growth below it", () => {
		const chat = new TranscriptContainer();
		const head = markerLines("head-", 4);
		const block = new MutableLiveBlock([...head, "ticker · 0"]);
		chat.addChild(block);
		chat.render(80);

		// Let the ratchet over-promote through the quiet ticker, then tick it:
		// the floor lands on the ticker row (index 4).
		for (let i = 0; i < 70; i++) chat.render(80);
		expect(chat.getNativeScrollbackCommitSafeEnd()).toBe(5);
		block.setLines([...head, "ticker · 1"]);
		chat.render(80);

		// Settled rows are inserted above the ticker (append above stable
		// trailing chrome): the ticker shifts down and the floor must travel
		// with it, or the new settled rows would be barred from promoting.
		block.setLines([...head, "settled-a", "settled-b", "ticker · 1"]);
		for (let i = 0; i < 70; i++) chat.render(80);
		expect(chat.getNativeScrollbackCommitSafeEnd()).toBe(6);

		// And the shifted ticker itself never re-promotes.
		block.setLines([...head, "settled-a", "settled-b", "ticker · 2"]);
		for (let i = 0; i < 70; i++) chat.render(80);
		expect(chat.getNativeScrollbackCommitSafeEnd()).toBe(6);
	});
});

describe("tool live-region scrollback", () => {
	beforeAll(async () => {
		await initTheme();
		// The task progress renderer reads settings (resolved-model badge).
		await Settings.init({ inMemory: true, cwd: process.cwd() });
	});

	it("does not splice stale pending eval preview above the running eval viewport", async () => {
		if (process.platform === "win32") return;

		const term = new VirtualTerminal(120, 12);
		const tui = new TUI(term);
		const chat = new TranscriptContainer();
		const code = Array.from({ length: 20 }, (_unused, i) => `const line${i} = ${i};`).join("\n");
		const title = "call model with new prompt + check box heights";
		const args = { cells: [{ language: "js", title, code }] };
		const component = new ToolExecutionComponent("eval", args, {}, undefined, tui, process.cwd());

		try {
			chat.addChild(
				new Text("Now let me verify by calling the model and checking the box heights it produces:", 0, 0),
			);
			chat.addChild(new Text("prior filler\n".repeat(8).trimEnd(), 0, 0));
			tui.addChild(chat);
			tui.start();
			await term.waitForRender();

			chat.addChild(component);
			tui.requestRender();
			await term.waitForRender();

			component.updateResult(
				{
					content: [{ type: "text", text: "" }],
					details: { cells: [{ index: 0, title, code, language: "js", output: "", status: "running" }] },
				},
				true,
			);
			tui.requestRender();
			await term.waitForRender();

			const bufferText = term
				.getScrollBuffer()
				.map(row => Bun.stripANSI(row).trimEnd())
				.join("\n");
			expect(bufferText).not.toContain("pending [1/1]");
			expect(bufferText).toContain("const line9 = 9;");
			expect(bufferText).toContain("const line19 = 19;");
		} finally {
			component.stopAnimation();
			tui.stop();
			await term.flush();
		}
	});

	it("repaints a finalized write whose result lands after a card was appended below it", async () => {
		if (process.platform === "win32") return;

		const term = new VirtualTerminal(120, 20);
		const tui = new TUI(term);
		const chat = new TranscriptContainer();
		const content = Array.from({ length: 5 }, (_unused, i) => `const line${i} = ${i};`).join("\n");
		const args = { file_path: "packages/coding-agent/test/probe.ts", content };
		const component = new ToolExecutionComponent("write", args, {}, undefined, tui, process.cwd());

		try {
			chat.addChild(new Text("prior filler", 0, 0));
			tui.addChild(chat);
			tui.start();
			await term.waitForRender();

			// The write streams its preview while it is the live block.
			chat.addChild(component);
			tui.requestRender();
			await term.waitForRender();

			// An out-of-band card (e.g. a TTSR rule notification) is appended below
			// the still-in-flight write. Previously this froze the write on its
			// streaming preview, so the eventual result never repainted.
			chat.addChild(new Text("⚠ Injecting rule: ts-set-map", 0, 0));
			tui.requestRender();
			await term.waitForRender();

			const beforeResult = term
				.getScrollBuffer()
				.map(row => Bun.stripANSI(row).trimEnd())
				.join("\n");
			expect(beforeResult).toContain("(streaming)");

			// The write finishes after the card is already below it.
			component.updateResult({ content: [{ type: "text", text: "" }], details: { path: args.file_path } }, false);
			tui.requestRender();
			await term.waitForRender();

			const afterResult = term
				.getScrollBuffer()
				.map(row => Bun.stripANSI(row).trimEnd())
				.join("\n");
			// The streaming preview is gone and the finalized header repainted in place.
			expect(afterResult).not.toContain("(streaming)");
			expect(afterResult).toContain("· 5 lines");
		} finally {
			component.stopAnimation();
			tui.stop();
			await term.flush();
		}
	});

	it("commits the scrolled-off head of an over-tall expanded streaming write to scrollback", async () => {
		if (process.platform === "win32") return;

		const term = new VirtualTerminal(120, 20);
		const tui = new TUI(term);
		const chat = new TranscriptContainer();
		const body = (n: number) => Array.from({ length: n }, (_unused, i) => `MARK-${i}`).join("\n");
		const filePath = "packages/coding-agent/test/probe.txt";
		// Expanded (Ctrl+O) lifts the tail-window cap, so the preview renders the
		// whole content top-anchored — append-only growth as chunks stream in.
		const component = new ToolExecutionComponent(
			"write",
			{ file_path: filePath, content: body(12) },
			{},
			undefined,
			tui,
			process.cwd(),
		);
		component.setExpanded(true);

		try {
			chat.addChild(component);
			tui.addChild(chat);
			tui.start();
			await term.waitForRender();

			for (const lineCount of [24, 40]) {
				component.updateArgs({ file_path: filePath, content: body(lineCount) });
				tui.requestRender();
				await term.waitForRender();
			}

			const scrollText = stripRows(term.getScrollBuffer());
			const viewportText = stripRows(term.getViewport());

			// MARK-0 scrolled above the viewport: it must live in native scrollback
			// (committed), not nowhere. Before the fix the tool block was not
			// append-only, so its scrolled-off head was dropped — a yanked stream.
			expect(viewportText).not.toContain("MARK-0");
			expect(scrollText).toContain("MARK-0");
			// The streaming tail stays on screen, and nothing went missing between.
			expect(viewportText).toContain("MARK-39");
			expect(viewportText).toContain("(streaming)");
			expect(scrollText).toContain("MARK-20");
		} finally {
			component.stopAnimation();
			tui.stop();
			await term.flush();
		}
	});

	it("commits the scrolled-off head of an over-tall pending task context to scrollback", async () => {
		if (process.platform === "win32") return;

		const term = new VirtualTerminal(120, 12);
		const tui = new TUI(term);
		const chat = new TranscriptContainer();
		const context = (n: number) => Array.from({ length: n }, (_unused, i) => `- CTX-${i}`).join("\n");
		const args = (n: number) => ({
			agent: "task",
			context: context(n),
			tasks: [{ id: "alpha", description: "probe", assignment: "Inspect the task context." }],
		});
		const component = new ToolExecutionComponent("task", args(4), {}, undefined, tui, process.cwd());

		try {
			chat.addChild(component);
			tui.addChild(chat);
			tui.start();
			await term.waitForRender();

			for (const lineCount of [12, 24, 40]) {
				component.updateArgs(args(lineCount));
				tui.requestRender();
				await term.waitForRender();
			}

			const scrollText = stripRows(term.getScrollBuffer());
			const viewportText = stripRows(term.getViewport());

			expect(viewportText).not.toContain("CTX-0");
			expect(scrollText).toContain("CTX-0");
			expect(scrollText).toContain("CTX-20");
			expect(viewportText).toContain("CTX-39");
		} finally {
			component.stopAnimation();
			tui.stop();
			await term.flush();
		}
	});

	it("keeps the static task context reachable in scrollback while progress ticks below it", async () => {
		if (process.platform === "win32") return;

		const term = new VirtualTerminal(120, 12);
		const tui = new TUI(term);
		const chat = new TranscriptContainer();
		const context = Array.from({ length: 40 }, (_unused, i) => `- CTX-${i}`).join("\n");
		const args = {
			agent: "explore",
			context,
			tasks: [{ id: "alpha", description: "probe", assignment: "Inspect the repo." }],
		};
		const component = new ToolExecutionComponent("task", args, {}, undefined, tui, process.cwd());
		const progressAt = (toolCount: number) => ({
			index: 0,
			id: "alpha",
			agent: "explore",
			agentSource: "bundled" as const,
			status: "running" as const,
			task: "probe",
			description: "probe",
			recentTools: [],
			recentOutput: [],
			toolCount,
			tokens: 0,
			cost: 0,
			durationMs: toolCount * 250,
		});
		const partial = (toolCount: number) =>
			component.updateResult(
				{
					content: [{ type: "text", text: "" }],
					details: {
						projectAgentsDir: null,
						results: [],
						totalDurationMs: 0,
						progress: [progressAt(toolCount)],
					},
				},
				true,
			);

		try {
			chat.addChild(component);
			tui.addChild(chat);
			tui.start();
			await term.waitForRender();

			// A running task rewrites its progress line (tool counts, spinner)
			// below the static context for the whole run. The context head that
			// scrolled above the viewport must still reach native scrollback —
			// previously the ticking tail suspended commits for the entire
			// block, leaving the context neither in history nor on screen.
			// Two full promotion windows: the call→result transition frame
			// poisons the first window's minimum, the second promotes the head.
			for (let i = 1; i <= 70; i++) {
				partial(i);
				tui.requestRender();
				await term.waitForRender();
			}

			const scrollText = stripRows(term.getScrollBuffer());
			const viewportText = stripRows(term.getViewport());

			expect(viewportText).not.toContain("CTX-0");
			expect(scrollText).toContain("CTX-0");
			expect(scrollText).toContain("CTX-20");
		} finally {
			component.stopAnimation();
			tui.stop();
			await term.flush();
		}
	}, 20000);

	it("stops growing scrollback once slow-ticking rows are floored (no recommit storm)", async () => {
		if (process.platform === "win32") return;

		// The duplication-storm shape from the field: a live block whose head is
		// static context, whose tail is a slowly-ticking agent tree plus a
		// spinner, with finalized content (IRC cards) piled below it. The pile
		// pushes the ticker rows above the window top, so any over-promotion
		// commits them; every later tick would then make the engine audit
		// recommit — native scrollback gains a stale snapshot of the tree per
		// tick for the entire run. With the rewrite floor the ratchet converges
		// after the first promoted-row re-tick and scrollback stops growing.
		const term = new VirtualTerminal(80, 10);
		const tui = new TUI(term);
		const chat = new TranscriptContainer();
		const head = markerLines("CTX-", 20);
		const spinner = ["⠋", "⠙", "⠹", "⠸", "⠼", "⠴", "⠦", "⠧"];
		let frameSeq = 0;
		const liveLines = (a: number, b: number) => [
			...head,
			`agent-one · ${a} tools`,
			`agent-two · ${b} tools`,
			`${spinner[frameSeq % spinner.length]} running`,
		];
		const block = new MutableLiveBlock(liveLines(0, 0));
		chat.addChild(block);
		chat.addChild(new MutableLiveBlock(markerLines("IRC-", 15), true));

		const counters: [number, number] = [0, 0];
		const renderFrames = async (frames: number) => {
			for (let i = 0; i < frames; i++) {
				frameSeq++;
				block.setLines(liveLines(...counters));
				tui.requestRender();
				await term.waitForRender();
			}
		};
		const tick = async (which: 0 | 1, frames: number) => {
			counters[which] += 1;
			await renderFrames(frames);
		};

		try {
			tui.addChild(chat);
			tui.start();
			await term.waitForRender();

			// Overshoot: a quiet stretch longer than the promotion window lets
			// the ratchet promote (and the engine commit) the ticker rows.
			await renderFrames(35);
			// First post-promotion tick of the topmost ticker arms the floor.
			await tick(0, 35);
			const settled = stripRows(term.getScrollBuffer());

			// Further slow ticks must not grow native scrollback at all.
			await tick(1, 12);
			await tick(0, 12);
			await tick(1, 12);
			expect(stripRows(term.getScrollBuffer())).toBe(settled);

			// The static head still reached scrollback. The ticker rows sit in
			// the hidden gap between the commit boundary and the window top
			// (the accepted cost while finalized content is piled below a live
			// block) — but history holds exactly one stale snapshot of them
			// instead of one per tick.
			expect(settled).toContain("CTX-0");
			const staleSnapshots = settled.split("\n").filter(row => row.startsWith("agent-one ·")).length;
			expect(staleSnapshots).toBeLessThanOrEqual(2);
		} finally {
			tui.stop();
			await term.flush();
		}
	}, 30000);

	it("commits the scrolled-off head of a tall finalized bottom tool result", async () => {
		if (process.platform === "win32") return;

		const term = new VirtualTerminal(120, 12);
		const tui = new TUI(term);
		const chat = new TranscriptContainer();
		const content = markerLines("FINAL-", 40).join("\n");
		const args = { path: "packages/coding-agent/test/finalized.txt" };
		const component = new ToolExecutionComponent("read", args, {}, undefined, tui, process.cwd());
		component.setExpanded(true);
		component.updateResult(
			{
				content: [{ type: "text", text: content }],
				details: { displayContent: { text: content, startLine: 1 } },
			},
			false,
		);

		try {
			chat.addChild(component);
			tui.addChild(chat);
			tui.start();
			await term.waitForRender();

			const scrollText = stripRows(term.getScrollBuffer());
			const viewportText = stripRows(term.getViewport());

			expect(viewportText).not.toContain("FINAL-0");
			expect(scrollText).toContain("FINAL-0");
			expect(scrollText).toContain("FINAL-20");
			expect(viewportText).toContain("FINAL-39");
		} finally {
			component.stopAnimation();
			tui.stop();
			await term.flush();
		}
	});

	it("keeps a re-layouting live block's changed head out of scrollback", async () => {
		if (process.platform === "win32") return;

		const term = new VirtualTerminal(120, 12);
		const tui = new TUI(term);
		const chat = new TranscriptContainer();
		const block = new MutableLiveBlock(markerLines("OLD-", 8));

		try {
			chat.addChild(block);
			tui.addChild(chat);
			tui.start();
			await term.waitForRender();

			block.setLines(markerLines("NEW-", 40));
			tui.requestRender();
			await term.waitForRender();

			const scrollText = stripRows(term.getScrollBuffer());
			const viewportText = stripRows(term.getViewport());

			expect(viewportText).not.toContain("NEW-0");
			expect(scrollText).not.toContain("NEW-0");
			expect(scrollText).not.toContain("NEW-20");
			expect(viewportText).toContain("NEW-39");
		} finally {
			tui.stop();
			await term.flush();
		}
	});

	it("commits the scrolled-off head of an expanded eval whose output streams past the viewport", async () => {
		if (process.platform === "win32") return;

		const term = new VirtualTerminal(120, 12);
		const tui = new TUI(term);
		const chat = new TranscriptContainer();
		const title = "stream lots of output";
		const code = "for (let i = 0; i < 40; i++) console.log('MARK-' + i);";
		const args = { cells: [{ language: "js", title, code }] };
		const component = new ToolExecutionComponent("eval", args, {}, undefined, tui, process.cwd());
		component.setExpanded(true);
		const out = (n: number) => Array.from({ length: n }, (_unused, i) => `MARK-${i}`).join("\n");
		const partial = (output: string) =>
			component.updateResult(
				{
					content: [{ type: "text", text: "" }],
					details: { cells: [{ index: 0, title, code, language: "js", output, status: "running" }] },
				},
				true,
			);

		partial(out(4));

		try {
			chat.addChild(component);
			tui.addChild(chat);
			tui.start();
			await term.waitForRender();

			for (const lineCount of [12, 24, 40]) {
				partial(out(lineCount));
				tui.requestRender();
				await term.waitForRender();
			}

			const scrollText = stripRows(term.getScrollBuffer());
			const viewportText = stripRows(term.getViewport());

			// The streamed output head scrolled above the viewport: it must live in
			// native scrollback (committed), not nowhere. The fixed code cell rides
			// along as the stable prefix above it.
			expect(viewportText).not.toContain("MARK-0");
			expect(scrollText).toContain("MARK-0");
			expect(scrollText).toContain("MARK-20");
			// The streaming tail stays on screen, and nothing went missing between.
			expect(viewportText).toContain("MARK-39");
		} finally {
			component.stopAnimation();
			tui.stop();
			await term.flush();
		}
	});
});

function makeAssistantMessage(text: string): AssistantMessage {
	return {
		role: "assistant",
		content: [{ type: "text", text }],
		api: "anthropic",
		provider: "anthropic",
		model: "test-model",
		usage: {
			input: 0,
			output: 0,
			cacheRead: 0,
			cacheWrite: 0,
			totalTokens: 0,
			cost: { input: 0, output: 0, cacheRead: 0, cacheWrite: 0, total: 0 },
		},
		stopReason: "stop",
		timestamp: Date.now(),
	};
}

function makeThinkingMessage(thinking: string): AssistantMessage {
	const message = makeAssistantMessage("");
	message.content = [{ type: "thinking", thinking }];
	return message;
}

describe("assistant live-region scrollback", () => {
	beforeAll(async () => {
		await initTheme();
		await Settings.init({ inMemory: true, cwd: process.cwd() });
	});

	it("commits a streamed reply's scrolled-off head to scrollback instead of dropping it", async () => {
		if (process.platform === "win32") return;

		const term = new VirtualTerminal(120, 12);
		const tui = new TUI(term);
		const chat = new TranscriptContainer();
		// A streaming assistant reply, mid-stream (no message in the ctor → live).
		// A markdown list yields one stable row per item, so growth is append-only.
		const component = new AssistantMessageComponent(undefined, false);
		const markers = Array.from({ length: 40 }, (_unused, i) => `- MARK-${i}`);

		try {
			chat.addChild(component);
			tui.addChild(chat);
			tui.start();
			await term.waitForRender();

			component.updateContent(makeAssistantMessage(markers.slice(0, 4).join("\n")));
			tui.requestRender();
			await term.waitForRender();

			for (const lineCount of [12, 24, 40]) {
				component.updateContent(makeAssistantMessage(markers.slice(0, lineCount).join("\n")));
				tui.requestRender();
				await term.waitForRender();
			}

			const scrollText = stripRows(term.getScrollBuffer());
			const viewportText = stripRows(term.getViewport());

			// MARK-0 scrolled above the viewport: with the fix it lives in native
			// scrollback (committed), not nowhere. The regression dropped it.
			expect(viewportText).not.toContain("MARK-0");
			expect(scrollText).toContain("MARK-0");
			// The tail is still on screen, and nothing went missing in between.
			expect(viewportText).toContain("MARK-39");
			expect(scrollText).toContain("MARK-20");
		} finally {
			tui.stop();
			await term.flush();
		}
	});

	it("commits scrolled-off styled thinking paragraphs to scrollback while streaming", async () => {
		if (process.platform === "win32") return;

		const term = new VirtualTerminal(120, 12);
		const tui = new TUI(term);
		const chat = new TranscriptContainer();
		const component = new AssistantMessageComponent(undefined, false);
		// Word-wrapped italic/colored paragraphs — the styled streaming shape the
		// raw-byte append detector mis-classified as volatile (the span-closing
		// SGR moves rows as the paragraph wraps), which froze the commit boundary
		// and dropped every later paragraph that scrolled past the viewport top.
		const paragraphs = Array.from(
			{ length: 8 },
			(_unused, i) =>
				`PARA-${i} considering the resolver path and the descriptor defaults, the policy layer must keep the ` +
				`reasoning flag intact while discovery maps an unknown model entry onto the bundled reference shape ` +
				`so the runtime request stays correct across upstream metadata shifts.`,
		);
		const fullText = paragraphs.join("\n\n");
		const words = fullText.split(" ");

		try {
			chat.addChild(component);
			tui.addChild(chat);
			tui.start();
			await term.waitForRender();

			// Stream a few words per frame so the in-flight bottom line extends,
			// wraps, and sheds words onto new rows across many coalesced frames.
			for (let i = 5; i <= words.length; i += 5) {
				component.updateContent(makeThinkingMessage(words.slice(0, i).join(" ")));
				tui.requestRender();
				await term.waitForRender();
			}

			const scrollText = stripRows(term.getScrollBuffer());
			const viewportText = stripRows(term.getViewport());

			// Early paragraphs scrolled above the viewport: they must live in
			// native scrollback, not vanish into the dropped gap.
			expect(viewportText).not.toContain("PARA-0");
			expect(scrollText).toContain("PARA-0");
			expect(scrollText).toContain("PARA-4");
			// The tail is still on screen.
			expect(viewportText).toContain("PARA-7");
		} finally {
			tui.stop();
			await term.flush();
		}
	});
});