fix(tui): normalize tabs for terminal output (#6697)

packages/tui/src/utils.ts

@@ -274,14 +274,35 @@ export function visibleWidth(str: string): number {
  * Normalize text for terminal output without changing logical editor content.
  * Some terminals render precomposed Thai/Lao AM vowels inconsistently during
  * differential repaint. Their compatibility decompositions have the same cell
- * width but avoid stale-cell artifacts in terminal renderers.
+ * width but avoid stale-cell artifacts in terminal renderers. Visible tabs are
+ * expanded to the fixed width used by layout so terminal tab stops cannot wrap
+ * a logical line, while tabs inside terminal string sequences stay untouched.
  */
 const THAI_LAO_AM_REGEX = /[\u0e33\u0eb3]/;
 const THAI_LAO_AM_GLOBAL_REGEX = /[\u0e33\u0eb3]/g;
 
 export function normalizeTerminalOutput(str: string): string {
-	if (!THAI_LAO_AM_REGEX.test(str)) return str;
-	return str.replace(THAI_LAO_AM_GLOBAL_REGEX, (char) => (char === "\u0e33" ? "\u0e4d\u0e32" : "\u0ecd\u0eb2"));
+	let normalized = str;
+	if (THAI_LAO_AM_REGEX.test(normalized)) {
+		normalized = normalized.replace(THAI_LAO_AM_GLOBAL_REGEX, (char) =>
+			char === "\u0e33" ? "\u0e4d\u0e32" : "\u0ecd\u0eb2",
+		);
+	}
+	if (!normalized.includes("\t")) return normalized;
+
+	let result = "";
+	let i = 0;
+	while (i < normalized.length) {
+		const ansi = extractAnsiCode(normalized, i);
+		if (ansi) {
+			result += ansi.code;
+			i += ansi.length;
+			continue;
+		}
+		result += normalized[i] === "\t" ? "   " : normalized[i];
+		i++;
+	}
+	return result;
 }
 
 /**

packages/tui/test/tab-width.test.ts

@@ -1,6 +1,37 @@
 import assert from "node:assert";
 import { describe, it } from "node:test";
-import { extractSegments, sliceWithWidth, visibleWidth } from "../src/utils.ts";
+import { type Component, TUI } from "../src/tui.ts";
+import { extractSegments, normalizeTerminalOutput, sliceWithWidth, visibleWidth } from "../src/utils.ts";
+import { VirtualTerminal } from "./virtual-terminal.ts";
+
+class FullViewportContent implements Component {
+	render(width: number): string[] {
+		return ["base 0", "base 1", "base 2"].map((line) => line.padEnd(width));
+	}
+
+	invalidate(): void {}
+}
+
+class CapturingVirtualTerminal extends VirtualTerminal {
+	private output = "";
+
+	override write(data: string): void {
+		this.output += data;
+		super.write(data);
+	}
+
+	getOutput(): string {
+		return this.output;
+	}
+}
+
+class TabStatusOverlay implements Component {
+	render(): string[] {
+		return ["\tX"];
+	}
+
+	invalidate(): void {}
+}
 
 describe("tab width accounting", () => {
 	it("keeps slice helper widths consistent with visible width", () => {
@@ -25,4 +56,32 @@ describe("tab width accounting", () => {
 		assert.strictEqual(tabFits.beforeWidth, 11);
 		assert.strictEqual(visibleWidth(tabFits.before), tabFits.beforeWidth);
 	});
+
+	it("keeps tabs inside terminal control sequences byte-identical", () => {
+		const controlSequences = [
+			"\x1b]8;;https://example.test/a\tb\x07",
+			"\x1b]0;window\ttitle\x1b\\",
+			"\x1b_payload\tdata\x1b\\",
+		];
+
+		for (const controlSequence of controlSequences) {
+			assert.strictEqual(normalizeTerminalOutput(`${controlSequence}label\ttext`), `${controlSequence}label   text`);
+		}
+	});
+
+	it("keeps tab-containing overlays on one physical terminal row", async () => {
+		const terminal = new CapturingVirtualTerminal(16, 3);
+		const tui = new TUI(terminal);
+		tui.addChild(new FullViewportContent());
+		tui.showOverlay(new TabStatusOverlay(), { width: 4, row: 1, col: 4 });
+		tui.start();
+
+		try {
+			await terminal.waitForRender();
+			assert.deepStrictEqual(terminal.getViewport(), ["base 0          ", "base   X        ", "base 2          "]);
+			assert.ok(!terminal.getOutput().includes("\t"));
+		} finally {
+			tui.stop();
+		}
+	});
 });