Create a manual handoff

Creates a one-way human ownership episode for payer interaction work. Use this endpoint only when the current `nextAction.type` is `complete_payer_interaction` and `nextAction.resolution.kind` is `manual_handoff`. Customer calls during `processing` are rejected with `manual_handoff_not_allowed`. Creating a handoff does not prove payer submission or receipt. Once active, mutating automation does not resume for that interaction lineage. ## Returns Returns the durable `ManualHandoff`.