Optional organizationOptional retrievalOptional maxOptional topKByOptional per-scope retrieval caps. Implementations are free to ignore/override.
Optional turnWith a learning layer: the turn's scope ids, from the GMI's learner session. A retriever reads the user, persona and conversation scopes under them (a learner's, or the session's own form on a turn with no learner); without them it reads under the plain ids, as with no layer.
Advisory character budget for the returned context string. Implementations may truncate to stay within this budget.