After a bit more analysis and the discovery of the handling of Result.autocreate implementation in Moodle, I've revised the proposed flow for Grade Item creation.
The key here is that: in the new flow (autocreate: true) regardless that the Tool requires a grade (either by capability OR explicit settings for manual deployment) a grade book column will only be created if there is an explicit Line Item section in the Content Item payload.
Hoping to hear if that makes sense?
Thanks!
Claude