Advances the flow by answering the current step. The body depends on the last presentation's type — do not mix the two shapes:

• decision: send only choice (a step_id from options). Do not send option_index or values.
• form: send option_index (index into options) and values (field name → string). Do not send choice.

Do not call /resolve for detection_failed, authenticated, or failed. For retryable detection_failed, a timeout, or a 409 (another transition still in flight), poll GET .../state/{session_id} until a decision/form/authenticated view appears, then continue. If detection_failed is not retryable, open live_view_url to finish signing in.

{
  "values": {
    "username": "user@example.com",
    "password": "secret"
  }
}