default_build_packet_envelope

def default_build_packet_envelope(
    channel_id: str,
    sender_id: str,
    body: str,
    *,
    handoff: "Handoff | None" = None,
    context_set: dict | None = None,
    audience: list[str] | None = None,
    causation_id: str | None = None,
) -> Envelope:
    """Default ``build_packet_envelope``: emit ``EV_PACKET`` with body +
    optional routing.

    ``routing`` carries ``{"kind": "handoff", "target": ..., "reason": ...}``
    when ``handoff`` is set. ``context_set`` populates ``context``.
    """
    event_data: dict[str, object] = {"body": body}
    if handoff is not None:
        routing: dict[str, object] = {"kind": "handoff", "target": handoff.target}
        if handoff.reason:
            routing["reason"] = handoff.reason
        event_data["routing"] = routing
    if context_set:
        event_data["context"] = dict(context_set)
    return Envelope(
        channel_id=channel_id,
        sender_id=sender_id,
        audience=audience,
        event_type=EV_PACKET,
        event_data=event_data,
        causation_id=causation_id,
    )