diff --git a/crates/ailang-core/src/ast.rs b/crates/ailang-core/src/ast.rs
index 36d903a..20020d3 100644
--- a/crates/ailang-core/src/ast.rs
+++ b/crates/ailang-core/src/ast.rs
@@ -1,10 +1,12 @@
 //! AST nodes for the AILang language.
 //!
-//! Every type in this module is the in-memory mirror of a node in the
-//! AILang JSON schema documented in `docs/DESIGN.md`. The serde
-//! attributes carry the schema: field renames (`as`, `type`, `fn`,
-//! `paramTypes`, `retType`), enum tags (`kind`, `t`, `k`, `p`), and
-//! `skip_serializing_if` predicates that keep the canonical-JSON
+//! **The canonical schema lives in `docs/DESIGN.md` §"Data model"**;
+//! this module is the Rust-side projection of it. When the two drift,
+//! `crates/ailang-core/tests/design_schema_drift.rs` fires.
+//!
+//! The serde attributes carry the schema: field renames (`as`, `type`,
+//! `fn`, `paramTypes`, `retType`), enum tags (`kind`, `t`, `k`, `p`),
+//! and `skip_serializing_if` predicates that keep the canonical-JSON
 //! representation backwards compatible across schema extensions.
 //!
 //! The entry type is [`Module`]. The two helpers [`def_name`] and