Call state

agent.state returns a CallState — a call’s current phase. Compare it against the State::* constants, usually inside await_until:

await_until(|| assert(callee.state).equals(State::Ringing));

• State::Idle — No active call.
• State::Ringing — A call is ringing — incoming or outgoing — but not yet answered.
• State::Established — The call is connected and media is flowing.