## Summary
Two documentation improvements for the AI chat docs.
**Head-start persistence contract.** The fast starts page now documents
what your hooks can rely on across a head-start handover: one stable
assistant `messageId` for the whole turn, `onTurnComplete` as the
canonical persistence point, reasoning parts flowing into durable
history, and how Head Start composes with `hydrateMessages` (the
first-turn history arrives as `incomingMessages`, and the runtime
splices the warm partial onto the hydrated chain, deduplicated by id).
The hydrate examples on the lifecycle hooks and database persistence
pages now upsert their conversation row, since head-start first turns
run without a preload to create it.
**Sessions page.** The page opened with "a durable, task-bound,
bi-directional I/O channel pair", which reads as jargon and omitted run
orchestration entirely. It now leads with the plain mental model (a pair
of durable streams: input carries user messages, output carries
everything the agent produces) plus the Session's role orchestrating
runs, a diagram, a minimal runnable example, and a section on the
one-session-many-runs lifecycle.
Documents behavior shipping in
[#3907](https://github.com/triggerdotdev/trigger.dev/pull/3907).
Eric Allam
84809b02ca