feat(ui): add ask keymap help modal

tests/help-modal.test.ts

@@ -0,0 +1,68 @@
+import assert from "node:assert/strict";
+import test from "node:test";
+import { visibleWidth } from "@mariozechner/pi-tui";
+import { ASK_HELP_CLOSE_HINT, ASK_KEYMAPS } from "../src/constants/keymaps.ts";
+import { AskHelpModal } from "../src/ui/help-modal.ts";
+
+const noop = () => {
+	// Test callback intentionally does nothing.
+};
+
+function plainTheme() {
+	return {
+		fg(_color: string, text: string) {
+			return text;
+		},
+		bg(_color: string, text: string) {
+			return text;
+		},
+	};
+}
+
+test("help modal renders compactly on phone-width screens", () => {
+	const modal = new AskHelpModal(plainTheme(), noop);
+	const lines = modal.render(28);
+
+	assert(lines.length > ASK_KEYMAPS.length + 4);
+	assert(lines.every((line) => visibleWidth(line) <= 28));
+	assert(lines.join("\n").includes("@eko24ive/pi-ask"));
+	assert(lines.slice(-3, -1).join(" ").includes("Esc, Ctrl+C, or ?"));
+	assert(lines.includes("│ ?                        │"));
+	assert(lines.includes("│   Show this menu         │"));
+});
+
+test("help modal keeps context rows on wider screens", () => {
+	const modal = new AskHelpModal(plainTheme(), noop);
+	const lines = modal.render(72);
+
+	assert(lines.length > ASK_KEYMAPS.length + 4);
+	assert(lines.join("\n").includes("Main flow"));
+	assert(lines.at(-2)?.includes(ASK_HELP_CLOSE_HINT));
+});
+
+test("help modal closes from configured keyboard shortcuts", () => {
+	for (const input of ["?", "\u001b", "\u0003"]) {
+		let closed = 0;
+		const modal = new AskHelpModal(plainTheme(), () => {
+			closed += 1;
+		});
+
+		modal.handleInput(input);
+
+		assert.equal(closed, 1);
+	}
+});
+
+test("help modal ignores enter and closes idempotently on dispose", () => {
+	let closed = 0;
+	const modal = new AskHelpModal(plainTheme(), () => {
+		closed += 1;
+	});
+
+	modal.handleInput("\r");
+	assert.equal(closed, 0);
+
+	modal.dispose();
+	modal.dispose();
+	assert.equal(closed, 1);
+});