Host route that finalizes tokenize-first payments; undefined disables auto-completion.
fieldsOwnerRef
fieldsOwnerRef:RefObject<object|null>
Identity of the instance holding the single mount slot.
Claimed synchronously when its mount effect starts (before the async SDK
load), so a second concurrent instance is rejected instead of silently
stealing the slot.
Host route that finalizes tokenize-first payments; undefined disables auto-completion.