How do I detect backfill completion with S3 destinations?

reference_id is only populated if you pass it when connecting users (in the widget session or the generateAuthToken call); otherwise it is null.

reference_id is only populated if you pass it when connecting users (in the widget session or the generateAuthToken call); otherwise it is null.

You can still map user_id to reference_id from the auth event files. Every S3 file is named {user_id}-{start_time}.json and carries user.user_id in the body.

For S3 there is no explicit backfill-completion signal (the terra-reference chunk count only applies to webhook destinations). Treat historical files as done once the start_time values in the filenames catch up to the present.