Extract auto-reply helpers into modules

src/runtime.ts

@@ -0,0 +1,14 @@
+export type RuntimeEnv = {
+	log: typeof console.log;
+	error: typeof console.error;
+	exit: (code: number) => never;
+};
+
+export const defaultRuntime: RuntimeEnv = {
+	log: console.log,
+	error: console.error,
+	exit: (code) => {
+		process.exit(code);
+		throw new Error("unreachable"); // satisfies tests when mocked
+	},
+};