Sessions and Streaming: The Conversation Plumbing

The four nouns every agent platform reinvents — session, message, run, step — plus the two streams an agent UI needs (tokens and events), what it takes to reconnect to a long run without double-charging a customer, and the one decision that follows you forever: who stores the transcript, you or the platform.

Content current as of 2026-09.

Lessons

1. Four nouns: session, message, run, step
2. Two streams: tokens and events
3. Resumability: the run outlives the connection
4. Session state is not memory
5. Who holds the transcript: you or the platform