complete method
Implementation
AccumulatedTextStream? complete(String itemId, {String status = 'completed'}) {
final current = _items[itemId.trim()];
if (current == null) {
return null;
}
final next = AccumulatedTextStream(
itemId: current.itemId,
turnId: current.turnId,
status: status,
text: current.text,
senderName: current.senderName,
phase: current.phase,
);
_items[current.itemId] = next;
return next;
}