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## Summary

Documents the Sessions HTTP API for non-SDK and server-to-server
callers, which until now appeared only in the conceptual
[ai-chat/sessions](https://trigger.dev/docs/ai-chat/sessions) page.

## What's covered

- **Sessions API reference** —
`create`/`list`/`retrieve`/`update`/`close` added to the OpenAPI spec
and a new "Sessions API" group (`management/sessions/*`), mirroring the
Runs API.
- **Channel endpoints** — a reference page for the `.in`/`.out` realtime
HTTP endpoints (append, SSE read, records drain), the wire protocol,
`Last-Event-ID` resume, and the per-direction auth boundary (`.out`
append is secret-key only).
- **Session scopes** — `read:sessions:{id}` / `write:sessions:{id}` in
the authentication docs, with the capability boundary and the 1h token
TTL.

Cross-linked with the SDK-side `ai-chat/sessions` page. Verified by
rendering each page on the Mintlify dev server.