Per-experience token the client uses to poll.
Optionaldecision_Stable handle for outcome reporting; equals session_id on the generated path, null on cache hit.
Identifier of the generated experience.
Identifier of the generation session.
PENDING on async dispatch; COMPLETED on cache hit (widget_data is populated).
Optionalwidget_The capability's widget data — for /engage this is the decision envelope
(cast to DecisionEnvelope); null while PENDING (poll
GET /experiences/{id}, whose widget.data fills the same generic slot).
Single carrier — a duplicate decision_envelope field was removed to halve
the response now that it carries content blocks (engagement-content-blocks).
Result of invoking an engagement decision.