feat: add shared tty-input module (ask, editLine)

Extract duplicated ask() from commit.ts and pr.ts, and extract
the 100+ line inline raw-mode editor editMessage() from commit.ts
into a reusable editLine() with proper escape sequence buffering.

Co-Authored-By: Claude <noreply@anthropic.com>

src/tty-input.ts

@@ -0,0 +1,163 @@
+// Shared TTY input utilities used by command handlers.
+// Provides a simple line-input "ask" helper and a reusable inline
+// raw-mode text editor (used by both commit message editing and
+// interactive config editing).
+
+import * as readline from "node:readline";
+import { isStdinTTY } from "./tty";
+
+// ── Simple line input (cooked mode) ──────────────────────────────────
+
+export function ask(question: string): Promise<string> {
+	const rl = readline.createInterface({ input: process.stdin, output: process.stdout });
+	return new Promise((resolve) => {
+		rl.question(question, (answer) => {
+			rl.close();
+			resolve(answer.trim());
+		});
+	});
+}
+
+// ── Inline raw-mode editor ────────────────────────────────────────────
+//
+// Provides a simple line editor that runs in raw mode and supports:
+//   - Left/Right arrows, Home/End for cursor movement
+//   - Backspace / Delete for character removal
+//   - Ctrl+A (beginning), Ctrl+E (end), Ctrl+K (kill to end), Ctrl+U (kill to start)
+//   - Enter to confirm, Ctrl+C / Esc to cancel
+//
+// Returns the edited string, or null if the user cancelled.
+
+export interface EditResult {
+	value: string | null;
+}
+
+export async function editLine(initial: string): Promise<string | null> {
+	if (!isStdinTTY()) return null;
+
+	const savedRaw = process.stdin.isRaw;
+	process.stdin.setRawMode(true);
+	process.stdin.resume();
+
+	let buffer = initial;
+	let cursor = initial.length;
+
+	function render() {
+		// Clear line, move to start, show prompt + buffer, then reposition cursor
+		process.stdout.write("\r\x1b[2K  > " + buffer);
+		if (cursor < buffer.length) {
+			process.stdout.write(`\x1b[${buffer.length - cursor}D`);
+		}
+	}
+
+	process.stdout.write("  > " + buffer);
+
+	return new Promise((resolve) => {
+		let escapeBuf = "";
+
+		function finish(value: string | null) {
+			process.stdin.setRawMode(savedRaw === true);
+			process.stdin.pause();
+			process.stdin.removeAllListeners("data");
+			process.stdout.write("\n");
+			resolve(value);
+		}
+
+		function handleEscapeSeq(seq: string) {
+			switch (seq) {
+				case "\x1b[D": case "\x1bOD": // Left
+					if (cursor > 0) { cursor--; process.stdout.write("\x1b[D"); }
+					break;
+				case "\x1b[C": case "\x1bOC": // Right
+					if (cursor < buffer.length) { cursor++; process.stdout.write("\x1b[C"); }
+					break;
+				case "\x1b[H": case "\x1b[1~": case "\x1bOH": // Home
+					if (cursor > 0) { process.stdout.write(`\x1b[${cursor}D`); cursor = 0; }
+					break;
+				case "\x1b[F": case "\x1b[4~": case "\x1bOF": // End
+					if (cursor < buffer.length) { process.stdout.write(`\x1b[${buffer.length - cursor}C`); cursor = buffer.length; }
+					break;
+				case "\x1b[3~": // Delete
+					if (cursor < buffer.length) { buffer = buffer.slice(0, cursor) + buffer.slice(cursor + 1); render(); }
+					break;
+			}
+		}
+
+		process.stdin.on("data", (data: Buffer) => {
+			const key = data.toString();
+
+			// Ctrl+C
+			if (key === "\x03") { finish(null); return; }
+			// Esc
+			if (key === "\x1b") {
+				if (escapeBuf) {
+					// Already buffering — check if this completes a sequence
+					const next = escapeBuf + key;
+					if (/^(\x1b\[[0-9;]*[A-Za-z~]|\x1bO[A-Z])$/.test(next)) {
+						handleEscapeSeq(next);
+						escapeBuf = "";
+					} else {
+						// Treat lone Esc as cancel
+						finish(null);
+					}
+					return;
+				}
+				escapeBuf = "\x1b";
+				return;
+			}
+
+			// Buffering an escape sequence
+			if (escapeBuf) {
+				escapeBuf += key;
+				// Check if this completes a valid sequence
+				if (/^(\x1b\[[0-9;]*[A-Za-z~]|\x1bO[A-Z])$/.test(escapeBuf)) {
+					handleEscapeSeq(escapeBuf);
+					escapeBuf = "";
+				} else if (escapeBuf.length > 10 || /^[A-Za-z~]$/.test(key)) {
+					// Timeout or terminator that didn't match — discard
+					escapeBuf = "";
+				}
+				return;
+			}
+
+			// Enter
+			if (key === "\r" || key === "\n") {
+				const result = buffer.trim();
+				finish(result || null);
+				return;
+			}
+
+			// Backspace
+			if (key === "\x7f") {
+				if (cursor > 0) {
+					buffer = buffer.slice(0, cursor - 1) + buffer.slice(cursor);
+					cursor--;
+					render();
+				}
+				return;
+			}
+
+			// Ctrl+A → beginning of line
+			if (key === "\x01") {
+				if (cursor > 0) { process.stdout.write(`\x1b[${cursor}D`); cursor = 0; }
+				return;
+			}
+			// Ctrl+E → end of line
+			if (key === "\x05") {
+				if (cursor < buffer.length) { process.stdout.write(`\x1b[${buffer.length - cursor}C`); cursor = buffer.length; }
+				return;
+			}
+			// Ctrl+K → kill to end
+			if (key === "\x0b") { buffer = buffer.slice(0, cursor); render(); return; }
+			// Ctrl+U → kill to start
+			if (key === "\x15") { buffer = buffer.slice(cursor); cursor = 0; render(); return; }
+
+			// Printable characters
+			if (key >= " " && key !== "\x7f") {
+				buffer = buffer.slice(0, cursor) + key + buffer.slice(cursor);
+				cursor += key.length;
+				render();
+			}
+		});
+	});
+}