Most conversational state management assumes the conversation is happening — a chat session, a websocket, a context window. Email breaks that assumption rudely: a customer replies five days after your agent's last message, and your code is expected to pick up exactly where things left off, with no session, no socket, and a process that has restarted twelve times since. The good news: email already solved durable conversation tracking, decades ago, in three headers. Build on them properly and the