Fix TUI tab width accounting

closes #5218

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

@@ -0,0 +1,23 @@
+import assert from "node:assert";
+import { describe, it } from "node:test";
+import { extractSegments, sliceWithWidth, visibleWidth } from "../src/utils.ts";
+
+describe("tab width accounting", () => {
+	it("keeps slice helper widths consistent with visible width", () => {
+		const text = "out 192M\t.pi/skill-tests/results-ha";
+		const slice = sliceWithWidth(text, 0, 10, true);
+
+		assert.strictEqual(slice.text, "out 192M");
+		assert.strictEqual(slice.width, 8);
+		assert.strictEqual(visibleWidth(slice.text), slice.width);
+	});
+
+	it("keeps overlay segment widths consistent with visible width", () => {
+		const text = "out 192M\t.pi/skill-tests/results-ha";
+		const segments = extractSegments(text, 10, 13, 10, true);
+
+		assert.strictEqual(segments.before, "out 192M\t");
+		assert.strictEqual(segments.beforeWidth, 11);
+		assert.strictEqual(visibleWidth(segments.before), segments.beforeWidth);
+	});
+});