Require functions passed to conversation.external to return serializable values

[Loskir]

conversations/src/conversation.ts

Line 1173 in 9725eca

async external<F extends (...args: any[]) => any, I = any>(

Would be cool on a type level if possible. If not — return serialized and unserialized values so that the user notices it in runtime (and so that it's consistent between initial run and replays). Or maybe show a warning / throw an error if the value is not serializable