Raw SQL execution against a Barograph database.
Level 3 of the query layer (spec §9.2): always available, never second-class. Each call opens a short-lived read connection — WAL mode allows concurrent readers alongside the single writer, so reads never contend with the write path. A dedicated read pool replaces this when the Ecto integration lands.
Summary
Functions
Runs sql with positional (?1, ?2, …) parameters against the
database behind db.