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Sessions (§6)

A session is a long-lived ARCP context over one transport. It starts with a handshake, carries job traffic, and ends with session.close or transport drop.

Spec reference: §6.

Handshake

The Rust SDK names the v1.1 handshake messages SessionOpen, SessionAccepted, SessionRejected, and SessionUnauthenticated.

client  -> runtime  session.open
runtime -> client   session.accepted
        -> client   session.rejected or session.unauthenticated

Session<Unauthenticated> exposes only authenticate. A successful handshake returns Session<Authenticated>, which exposes job and runtime operations.

Capabilities

Capabilities declares optional surfaces such as anonymous auth, streaming, artifacts, subscriptions, model use, provisioned credentials, and feature support. The runtime advertises what it supports; the accepted session records the negotiated capabilities.

Ack and back-pressure

The runtime can be configured with RuntimeBuilder::with_ack_window. Once the number of emitted but unacknowledged countable envelopes reaches the window, writers pause until the client sends session.ack.

See examples/ack_backpressure.rs.

Heartbeat

session.ping and session.pong (ARCP v1.1 §6.4) keep long-lived sessions fresh and detect stalled peers. See examples/session_heartbeat/.

Listing and subscribing

The runtime implements session job listing plus generic and job-scoped subscriptions:

  • session.list_jobs for visible jobs in the session.
  • job.subscribe / job.unsubscribe for cross-session job observation.
  • subscribe / unsubscribe for filtered envelope fanout.

See examples/session_list_jobs/ and examples/job_subscribe/.

Closing

Either side may send session.close (SessionClosePayload). After close, job-scoped traffic must stop and the transport should be closed by the owner. In-flight jobs continue server-side and remain resumable until the runtime's retention window expires.