0123 — The codebase keeps `message_log`/`cursor`/`position` naming rather than renaming to events/consumers

Context. The fan-out design was planned in terms of “events” and “consumers”, while the code already uses message_log, cursor, and position from the log/queue split. The shapes are the same; only the names differ.

Decision. Keep the existing names. No rename churn to match the planning vocabulary.

Consequences. A reader of older planning material must map “events” to message_log and a consumer’s offset to cursor.position. In exchange, the schema, code, and labs stay internally consistent, and the codebase’s own nouns remain the single naming authority.