formatting and comments

apps/server-rust/src/db.rs

@@ -1,3 +1,10 @@
+//! PostgreSQL pool, migrations and low-level tenant-scoped queries.
+//!
+//! Multi-tenant tables use PostgreSQL row-level security in addition to owner
+//! columns and composite foreign keys. Every tenant query must execute inside a
+//! transaction after [`Db::set_tenant`], which uses `SET LOCAL` so pooled
+//! connections cannot retain the previous request's identity.
+
 use std::{fmt, str::FromStr};
 
 use deadpool_postgres::{Manager, ManagerConfig, Object, Pool, RecyclingMethod, Runtime};