An active Claude Code session backed by a long-lived CLI process.
Each session maintains a single CLI process whose stdin is kept open for multi-turn conversation. send writes a prompt to stdin; stream reads stdout until the next ResultMessage — see the hazard note on stream before correlating the two. The session is acquired as a Resource, which handles process cleanup on both normal exit and error.
The session ID assigned by the CLI, wrapped in IO since it reads a Ref.
The session ID assigned by the CLI, wrapped in IO since it reads a Ref.
Returns IO("pending") until the CLI emits an init SystemMessage or until the first turn completes (at which point the ResultMessage session ID is used).
Reads stdout messages until the next ResultMessage.
Reads stdout messages until the next ResultMessage.
HAZARD — the messages read are NOT "the reply to your last send". The underlying message queue is shared and long-lived across the whole session, and the CLI owns turn boundaries:
it emits output with no send in flight (a background task finishing resumes the main loop and produces a full extra ResultMessage), and
it merges a send issued while a turn is running into that turn, so the merged send never gets a ResultMessage of its own. Correlating send and stream positionally therefore attributes replies to the wrong message. At most one consumer may read at a time; concurrent readers silently split the messages between them. See docs/adr/0001-session-is-a-stream-not-turns.md.