Session control plane

A prompt sent while a session is working follows session.busy_input.default_mode, which defaults to steer. An idle session starts a normal turn. Explicit --queue, --steer, and --interrupt flags override the busy default for one send.

compozy session prompt sess_1234 "Prefer the smaller patch."
compozy session prompt sess_1234 "Run the next check." --queue
compozy session prompt sess_1234 "Change direction." --steer --expected-turn turn_1234 -o json

Steering uses the live agent's advertised capability. A successful injection preserves the active turn. If injection is unavailable or refused, CompozyOS records interrupt_fallback before canceling the current turn and dispatching the accepted replacement.

`steer_delivery`	Meaning
`injected`	Guidance was delivered into the active turn.
`pending_injection`	The agent accepted guidance and is waiting to inject it.
`interrupt_fallback`	CompozyOS accepted a replacement through the interrupt path.

The busy response contains disposition, steer_delivery, turn_id, entry_id, message_id, idempotency_key, queue_position, and replayed. Non-steering responses omit steer_delivery. HTTP and UDS return this object inside prompt; CLI JSON and native tools use the same envelope. Legacy status, delivery, and queue fields remain available during the compatibility window. Use steer_delivery for the injection outcome; legacy delivery describes dispatch scheduling.

An omitted expected_turn_id lets the daemon capture the current turn at admission. An explicit fence is strict: an obsolete ID returns 409 active_turn_mismatch with current_turn_id, before queue mutation or cancellation. CLI --expected-turn supplies this fence. The older --expected-turn-id flag remains supported with a deprecation warning until v0.5.0.

Keep both returned identities when retrying an uncertain send:

compozy session prompt sess_1234 "Prefer the smaller patch." \
  --message-id msg_original --idempotency-key idem_original

Reuse the original text, runtime, mode, and explicit fence. A changed request with the same identity returns send_conflict. A resolved steer acceptance replays the recorded delivery without injecting or canceling again.

compozy__session_prompt defaults to wait:false: it returns durable acceptance immediately. Set wait:true to wait for completion and receive a terminal runtime error if the turn fails. The follow-up preference is daemon-owned, so changing Follow-up behavior in Settings affects subsequent busy admissions through Web, CLI, HTTP, UDS, and native tools.