Read-only IAM, nothing more
The service account needs bigquery.jobs.create, bigquery.jobs.listAll, bigquery.datasets.get, bigquery.tables.get, bigquery.tables.list, bigquery.reservations.list, resourcemanager.projects.get, bigquery.readsessions.create, bigquery.readsessions.getData. Storage Read sessions are used only for INFORMATION_SCHEMA jobs, jobs timeline, and table storage results. SlashPeak never asks for roles/bigquery.dataViewer on your projects. The one optional exception is a linked Cloud Billing export, where you grant it on that single dataset of cost rows.
