pub async fn build_pool(config: &BackendConfig) -> Result<PgPool, EngineError>Expand description
Build a sqlx::PgPool from a BackendConfig whose connection
arm is BackendConnection::Postgres.
Returns EngineError::Unavailable { op: "pg.pool.build" } when
the config’s connection arm is not Postgres — the Valkey backend
has its own dial path, and a mis-routed config is a programmer
error the backend surfaces as a typed error rather than a panic.