From da6a2fb5eacb52aad46efc89708b0259841725fd Mon Sep 17 00:00:00 2001
From: Mario Zechner <badlogicgames@gmail.com>
Date: Sun, 11 Jan 2026 19:01:05 +0100
Subject: [PATCH] test(tui): cover style reset cases

---
 packages/tui/test/markdown.test.ts            | 48 +++++++++++++
 .../tui/test/tui-overlay-style-leak.test.ts   | 72 +++++++++++++++++++
 2 files changed, 120 insertions(+)
 create mode 100644 packages/tui/test/tui-overlay-style-leak.test.ts

diff --git a/packages/tui/test/markdown.test.ts b/packages/tui/test/markdown.test.ts
index d313902c..1bb2b240 100644
--- a/packages/tui/test/markdown.test.ts
+++ b/packages/tui/test/markdown.test.ts
@@ -1,12 +1,25 @@
 import assert from "node:assert";
 import { describe, it } from "node:test";
+import type { Terminal as XtermTerminalType } from "@xterm/headless";
 import { Chalk } from "chalk";
 import { Markdown } from "../src/components/markdown.js";
+import { type Component, TUI } from "../src/tui.js";
 import { defaultMarkdownTheme } from "./test-themes.js";
+import { VirtualTerminal } from "./virtual-terminal.js";
 
 // Force full color in CI so ANSI assertions are deterministic
 const chalk = new Chalk({ level: 3 });
 
+function getCellItalic(terminal: VirtualTerminal, row: number, col: number): number {
+	const xterm = (terminal as unknown as { xterm: XtermTerminalType }).xterm;
+	const buffer = xterm.buffer.active;
+	const line = buffer.getLine(buffer.viewportY + row);
+	assert.ok(line, `Missing buffer line at row ${row}`);
+	const cell = line.getCell(col);
+	assert.ok(cell, `Missing cell at row ${row} col ${col}`);
+	return cell.isItalic();
+}
+
 describe("Markdown component", () => {
 	describe("Nested lists", () => {
 		it("should render simple nested list", () => {
@@ -437,6 +450,41 @@ describe("Markdown component", () => {
 			// Should have bold codes (1 or 22 for bold on/off)
 			assert.ok(joinedOutput.includes("\x1b[1m"), "Should have bold code");
 		});
+
+		it("should not leak styles into following lines when rendered in TUI", async () => {
+			class MarkdownWithInput implements Component {
+				public markdownLineCount = 0;
+
+				constructor(private readonly markdown: Markdown) {}
+
+				render(width: number): string[] {
+					const lines = this.markdown.render(width);
+					this.markdownLineCount = lines.length;
+					return [...lines, "INPUT"];
+				}
+
+				invalidate(): void {
+					this.markdown.invalidate();
+				}
+			}
+
+			const markdown = new Markdown("This is thinking with `inline code`", 1, 0, defaultMarkdownTheme, {
+				color: (text) => chalk.gray(text),
+				italic: true,
+			});
+
+			const terminal = new VirtualTerminal(80, 6);
+			const tui = new TUI(terminal);
+			const component = new MarkdownWithInput(markdown);
+			tui.addChild(component);
+			tui.start();
+			await terminal.flush();
+
+			assert.ok(component.markdownLineCount > 0);
+			const inputRow = component.markdownLineCount;
+			assert.strictEqual(getCellItalic(terminal, inputRow, 0), 0);
+			tui.stop();
+		});
 	});
 
 	describe("Spacing after code blocks", () => {
diff --git a/packages/tui/test/tui-overlay-style-leak.test.ts b/packages/tui/test/tui-overlay-style-leak.test.ts
new file mode 100644
index 00000000..cf49f31b
--- /dev/null
+++ b/packages/tui/test/tui-overlay-style-leak.test.ts
@@ -0,0 +1,72 @@
+import assert from "node:assert";
+import { describe, it } from "node:test";
+import type { Terminal as XtermTerminalType } from "@xterm/headless";
+import { type Component, TUI } from "../src/tui.js";
+import { VirtualTerminal } from "./virtual-terminal.js";
+
+class StaticLines implements Component {
+	constructor(private readonly lines: string[]) {}
+
+	render(): string[] {
+		return this.lines;
+	}
+
+	invalidate(): void {}
+}
+
+class StaticOverlay implements Component {
+	constructor(private readonly line: string) {}
+
+	render(): string[] {
+		return [this.line];
+	}
+
+	invalidate(): void {}
+}
+
+function getCellItalic(terminal: VirtualTerminal, row: number, col: number): number {
+	const xterm = (terminal as unknown as { xterm: XtermTerminalType }).xterm;
+	const buffer = xterm.buffer.active;
+	const line = buffer.getLine(buffer.viewportY + row);
+	assert.ok(line, `Missing buffer line at row ${row}`);
+	const cell = line.getCell(col);
+	assert.ok(cell, `Missing cell at row ${row} col ${col}`);
+	return cell.isItalic();
+}
+
+async function renderAndFlush(tui: TUI, terminal: VirtualTerminal): Promise<void> {
+	tui.requestRender(true);
+	await new Promise<void>((resolve) => process.nextTick(resolve));
+	await terminal.flush();
+}
+
+describe("TUI overlay compositing", () => {
+	it("should not leak styles when a trailing reset sits beyond the last visible column (no overlay)", async () => {
+		const width = 20;
+		const baseLine = `\x1b[3m${"X".repeat(width)}\x1b[23m`;
+
+		const terminal = new VirtualTerminal(width, 6);
+		const tui = new TUI(terminal);
+		tui.addChild(new StaticLines([baseLine, "INPUT"]));
+		tui.start();
+		await renderAndFlush(tui, terminal);
+		assert.strictEqual(getCellItalic(terminal, 1, 0), 0);
+		tui.stop();
+	});
+
+	it("should not leak styles when overlay slicing drops trailing SGR resets", async () => {
+		const width = 20;
+		const baseLine = `\x1b[3m${"X".repeat(width)}\x1b[23m`;
+
+		const terminal = new VirtualTerminal(width, 6);
+		const tui = new TUI(terminal);
+		tui.addChild(new StaticLines([baseLine, "INPUT"]));
+
+		tui.showOverlay(new StaticOverlay("OVR"), { row: 0, col: 5, width: 3 });
+		tui.start();
+		await renderAndFlush(tui, terminal);
+
+		assert.strictEqual(getCellItalic(terminal, 1, 0), 0);
+		tui.stop();
+	});
+});