Function register_baseline_start 

pub async fn register_baseline_start(
    pool: &PgPool,
    tracking_table: &TrackingTable,
    version: u64,
    description: &str,
    checksum: &str,
    sections: &[(i32, MigrationSection)],
) -> Result<()>

Register a baseline as started: the main row (idempotent — ON CONFLICT DO NOTHING, so a resumed provision or later module adoption re-registers harmlessly) plus its Pending section rows. Ensures the main tracking table exists first (the section table is the caller’s precondition). See [register_start].