feat: add relay:tmux helper for relay watcher

src/cli/relay_tmux.ts

@@ -0,0 +1,29 @@
+import { spawn } from "node:child_process";
+
+const SESSION = "warelay-relay";
+
+export async function spawnRelayTmux(cmd = "pnpm warelay relay --verbose") {
+	await killSession(SESSION);
+	await new Promise<void>((resolve, reject) => {
+		const child = spawn("tmux", ["new", "-d", "-s", SESSION, cmd], {
+			stdio: "inherit",
+			shell: false,
+		});
+		child.on("error", reject);
+		child.on("exit", (code) => {
+			if (code === 0) resolve();
+			else reject(new Error(`tmux exited with code ${code}`));
+		});
+	});
+	return SESSION;
+}
+
+async function killSession(name: string) {
+	await new Promise<void>((resolve) => {
+		const child = spawn("tmux", ["kill-session", "-t", name], {
+			stdio: "ignore",
+		});
+		child.on("exit", () => resolve());
+		child.on("error", () => resolve());
+	});
+}