constraints: CHECK — check (<expr>) at create table & add column (ADR-0029)

The fourth constraint. `check ( <expr> )` reuses the ADR-0026
WHERE-expression grammar via `Subgrammar`, so a check is
written in the same language as a `where` filter.

- Grammar: a `CHECK_CONSTRAINT` arm joins the shared
  constraint-suffix Choice; `consume_check_expr` extracts the
  parenthesised expression (paren-depth aware) into
  `ColumnSpec.check` / `Command::AddColumn.check`.
- Storage: the parsed `Expr` is compiled once to inline SQL
  (`compile_check_sql` — `compile_expr` + ADR-0028's
  param-inliner) and stored in that form everywhere — a new
  `check_expr` column in `__rdbms_playground_columns`,
  `project.yaml`'s `ColumnSchema.check`, and the column DDL
  emitted by `do_create_table` / `schema_to_ddl`.
- `add column … check` routes through the rebuild primitive
  (SQLite's `ALTER … ADD COLUMN` cannot carry it); a CHECK on
  a serial/shortid column is create-table-only and refused at
  add-column with a friendly message.
- `describe` surfaces the CHECK. ADR-0029 §7/§8 updated to the
  SQL-form decision — double-quoted identifiers, consistent
  with ADR-0028's `explain` display SQL.

1201 tests pass (+8); clippy clean.

docs/adr/0029-column-constraints.md

@@ -80,7 +80,7 @@ A column spec gains an optional, repeatable constraint suffix
 **after** the `(type)` group:
 
 ```
-create table Books with pk isbn(text) check (length(isbn) = 13)
+create table Books with pk isbn(text) check (isbn like '978%')
 
 add column to Books: title (text) not null
 add column to Books: stock (int) default 0 check (stock >= 0)
@@ -283,28 +283,31 @@ the data.
 constraints must round-trip through `project.yaml` or they
 vanish on `rebuild` / `export` / `import`.
 
+The `CHECK` expression is stored — everywhere — as the
+**compiled SQL** form: the parsed `Expr` run through
+`compile_expr` with literals inlined (§4). Identifiers are
+double-quoted, exactly as ADR-0028's `explain` display SQL
+already renders them, so the form is consistent with what the
+learner already meets. (The original plan stored canonical
+*DSL text*; that needs both an `Expr`→text renderer and a
+text→`Expr` re-parser for the round-trip, while the rebuild
+path needs the SQL form regardless — storing SQL once removes
+both.)
+
 - **`project.yaml`** — the `ColumnSchema` record gains
-  `not_null: bool`, `default: Option<Value>`, and
+  `not_null: bool`, `default: Option<String>`, and
   `check: Option<String>`. (`unique: bool` already exists,
-  from ADR-0018's `serial` / `shortid` contract.) The `check`
+  from ADR-0018's `serial` / `shortid` contract.) `check`
-  expression is stored as its **canonical DSL text** — see the
+  holds the compiled SQL.
-  `Expr` text renderer below.
 - **Metadata table** — `NOT NULL`, `UNIQUE`, and `DEFAULT` are
   all recoverable from SQLite itself (`pragma_table_info`'s
   `notnull` and `dflt_value`; `pragma_index_list` origin `u`),
   so they need no metadata row. `CHECK` is *not* exposed by
-  any pragma — only by the raw `sqlite_master` SQL, which is
+  any pragma. So `__rdbms_playground_columns` carries a
-  in engine syntax. So `__rdbms_playground_columns` carries a
+  nullable `check_expr TEXT` column holding the compiled SQL,
-  nullable `check_expr TEXT` column holding the canonical DSL
+  which `schema_to_ddl` and `describe` echo verbatim. It is
-  text, keeping `describe` independent of engine-syntax
+  part of the internal table's `CREATE TABLE` definition —
-  parsing. It is part of the internal table's `CREATE TABLE`
+  there are no existing databases to migrate.
-  definition — there are no existing databases to migrate.
-- **`Expr` → DSL text renderer** — a new `render_expr` (small;
-  the `Expr` tree from ADR-0026 is shallow) produces canonical
-  DSL text for an expression. One renderer, three consumers:
-  `project.yaml` serialization, the `check_expr` metadata
-  column, and the structure view (§8). The check round-trips
-  text → `Expr` (re-parsed on load) → text.
 
 ### 8. Structure rendering
 
@@ -315,17 +318,17 @@ Option<String>`, and `check: Option<String>`.
 every constraint a column carries:
 
 ```
-┌───────┬──────┬───────────────────────────────────┐
+┌───────┬────────┬─────────────────────────────────┐
 │ Name  │ Type   │ Constraints                     │
-├───────┼──────┼───────────────────────────────────┤
+├───────┼────────┼─────────────────────────────────┤
 │ id    │ serial │ PK                              │
 │ email │ text   │ NOT NULL, UNIQUE                │
-│ age   │ int  │ DEFAULT 18, CHECK age >= 0        │
+│ age   │ int    │ DEFAULT 18, CHECK ("age" >= 0)  │
-└───────┴──────┴───────────────────────────────────┘
+└───────┴────────┴─────────────────────────────────┘
 ```
 
-The `CHECK` expression renders in DSL form (`render_expr`),
+The `CHECK` renders in its compiled-SQL form (§7) — the same
-not engine SQL.
+double-quoted-identifier style as ADR-0028's `explain` SQL.
 
 ### 9. PK columns — redundant and impossible constraints
 
@@ -409,10 +412,7 @@ additions:
   tables go through the ADR-0016 pretty-table renderer.
 - The internal metadata table `__rdbms_playground_columns`
   carries a new `check_expr` column — its first change since
-  ADR-0012.
+  ADR-0012 — holding the compiled-SQL form of the `CHECK`.
-- A new `Expr` → DSL-text renderer (`render_expr`) is added;
-  it is also reusable by any future feature that needs to
-  show an expression back to the user.
 - `project.yaml`'s `ColumnSchema` grows three fields; the
   format stays backward-compatible (the new keys default to
   "absent" — `not_null: false`, no `default`, no `check`).
@@ -433,8 +433,8 @@ A sensible build order, each step test-guarded:
    honour it, including the §6 `add column` rules. The
    `Expr` → SQL compile for `CHECK`.
 3. **Storage round-trip.** `ColumnSchema` fields, the
-   `check_expr` metadata column, `render_expr`, and the
+   `check_expr` metadata column, and the `project.yaml`
-   `project.yaml` read/write paths.
+   read/write paths.
 4. **`add constraint …` / `drop constraint …`.** The two
    commands, the rebuild-table path, and the §5 dry-run with
    its pretty-table refusals.

docs/simple-mode-limitations.md

@@ -48,3 +48,8 @@ entry names the ADR that drew the boundary.
   added afterward with `add column`. Creating a table with a
   mix of PK and non-PK columns in one statement needs
   advanced-mode `CREATE TABLE` syntax.
+- **`check (<expr>)` constraints reuse the WHERE-expression
+  grammar** (ADR-0026), so the same limits apply: no scalar
+  functions (`length(x)`), no arithmetic. A check is a boolean
+  combination of column-vs-literal comparisons, `LIKE`, `IN`,
+  `BETWEEN`, and `IS NULL`.

src/app.rs

@@ -2175,6 +2175,7 @@ mod tests {
                 primary_key: true,
                 unique: false,
                 default: None,
+                check: None,
             }],
             outbound_relationships: Vec::new(),
             inbound_relationships: Vec::new(),

src/db.rs

@@ -136,6 +136,9 @@ pub struct ColumnDescription {
     /// The column's `DEFAULT` expression as SQLite reports it,
     /// or `None` (ADR-0029).
     pub default: Option<String>,
+    /// The column's `CHECK` constraint in compiled-SQL form,
+    /// or `None` (ADR-0029).
+    pub check: Option<String>,
 }
 
 #[derive(Debug, Clone, PartialEq, Eq)]
@@ -1050,6 +1053,7 @@ fn configure_connection(conn: &Connection) -> Result<(), rusqlite::Error> {
              table_name TEXT NOT NULL,\n\
              column_name TEXT NOT NULL,\n\
              user_type TEXT NOT NULL,\n\
+             check_expr TEXT,\n\
              PRIMARY KEY (table_name, column_name)\n\
          ) STRICT;\n\
          CREATE TABLE IF NOT EXISTS {REL_TABLE} (\n\
@@ -1612,6 +1616,7 @@ fn read_schema_snapshot(conn: &Connection) -> Result<SchemaSnapshot, DbError> {
                 unique: c.unique,
                 not_null: c.notnull,
                 default: c.default_sql.clone(),
+                check: c.check.clone(),
                 // user_type is always populated for tables we
                 // created; the fallback is defensive.
                 user_type: c.user_type.unwrap_or(Type::Text),
@@ -1707,6 +1712,7 @@ fn read_table_snapshot(
             unique: c.unique,
             not_null: c.notnull,
             default: c.default_sql.clone(),
+            check: c.check.clone(),
         })
         .collect();
     let column_idents: Vec<String> = read
@@ -1816,6 +1822,63 @@ fn default_sql_literal(spec: &ColumnSpec) -> Result<Option<String>, DbError> {
     Ok(Some(sql_literal(&bound_to_sqlite_value(&bound))))
 }
 
+/// Compile a `CHECK` expression to inline SQL (ADR-0029 §4 /
+/// §7) — the form stored in the `check_expr` metadata column
+/// and emitted into column DDL. `compile_expr` produces
+/// `?N`-parameterised SQL; `inline_params_for_display`
+/// (ADR-0028) folds the literals back in, since DDL admits no
+/// parameters.
+fn compile_check_sql(expr: &Expr, schema: &ReadSchema) -> String {
+    let mut params: Vec<rusqlite::types::Value> = Vec::new();
+    let sql = compile_expr(expr, schema, &mut params);
+    inline_params_for_display(&sql, &params)
+}
+
+/// A minimal `ReadSchema` built from column specs — enough for
+/// `compile_expr` to resolve column types when compiling a
+/// `CHECK` at create-table time, before the table exists.
+fn read_schema_for_specs(columns: &[ColumnSpec], primary_key: &[String]) -> ReadSchema {
+    ReadSchema {
+        columns: columns
+            .iter()
+            .map(|c| ReadColumn {
+                name: c.name.clone(),
+                sqlite_type: c.ty.sqlite_strict_type().to_string(),
+                notnull: c.not_null,
+                primary_key: primary_key.contains(&c.name),
+                unique: c.unique,
+                default_sql: None,
+                check: None,
+                user_type: Some(c.ty),
+            })
+            .collect(),
+        primary_key: primary_key.to_vec(),
+        foreign_keys: Vec::new(),
+    }
+}
+
+/// Insert a column's row into the metadata table — the user
+/// type, plus the compiled `CHECK` SQL when present
+/// (ADR-0029 §7).
+fn insert_column_metadata(
+    conn: &Connection,
+    table: &str,
+    column: &str,
+    user_type: Type,
+    check_sql: Option<&str>,
+) -> Result<(), DbError> {
+    conn.execute(
+        &format!(
+            "INSERT INTO {META_TABLE} \
+                 (table_name, column_name, user_type, check_expr) \
+             VALUES (?1, ?2, ?3, ?4);"
+        ),
+        rusqlite::params![table, column, user_type.keyword(), check_sql],
+    )
+    .map_err(DbError::from_rusqlite)?;
+    Ok(())
+}
+
 fn do_create_table(
     conn: &Connection,
     persistence: Option<&Persistence>,
@@ -1843,8 +1906,17 @@ fn do_create_table(
     let single_inline_pk = primary_key.len() == 1 && columns.len() == 1
         && primary_key[0] == columns[0].name;
 
+    // Compile each column's CHECK once (ADR-0029 §4) — reused
+    // by the DDL clause and the metadata insert below. The
+    // minimal schema gives `compile_expr` the column types.
+    let check_schema = read_schema_for_specs(columns, primary_key);
+    let check_sqls: Vec<Option<String>> = columns
+        .iter()
+        .map(|c| c.check.as_ref().map(|e| compile_check_sql(e, &check_schema)))
+        .collect();
+
     let mut column_clauses: Vec<String> = Vec::with_capacity(columns.len());
-    for col in columns {
+    for (col, check_sql) in columns.iter().zip(&check_sqls) {
         let mut clause = format!(
             "{ident} {sqlite_type}",
             ident = quote_ident(&col.name),
@@ -1858,6 +1930,9 @@ fn do_create_table(
         // redundant declarations (ADR-0029 §9) so a PK column
         // never carries them here.
         clause.push_str(&column_constraints_sql(col)?);
+        if let Some(cs) = check_sql {
+            clause.push_str(&format!(" CHECK ({cs})"));
+        }
         column_clauses.push(clause);
     }
 
@@ -1884,17 +1959,8 @@ fn do_create_table(
         .unchecked_transaction()
         .map_err(DbError::from_rusqlite)?;
     tx.execute_batch(&ddl).map_err(DbError::from_rusqlite)?;
-    {
+    for (col, check_sql) in columns.iter().zip(&check_sqls) {
-        let mut stmt = tx
+        insert_column_metadata(&tx, name, &col.name, col.ty, check_sql.as_deref())?;
-            .prepare(&format!(
-                "INSERT INTO {META_TABLE} (table_name, column_name, user_type) \
-                 VALUES (?1, ?2, ?3);"
-            ))
-            .map_err(DbError::from_rusqlite)?;
-        for col in columns {
-            stmt.execute([name, col.name.as_str(), col.ty.keyword()])
-                .map_err(DbError::from_rusqlite)?;
-        }
     }
     let description = do_describe_table(conn, name)?;
     let changes = Changes {
@@ -1992,13 +2058,25 @@ fn do_add_column(
                 ty = column.ty.keyword(),
             )));
         }
+        // A CHECK on an auto-generated column is supported at
+        // `create table` time; adding one to a `serial` /
+        // `shortid` column afterwards is not (the auto-fill
+        // rebuild path does not thread it).
+        if column.check.is_some() {
+            return Err(DbError::Unsupported(format!(
+                "a `check` constraint on the auto-generated column `{}` \
+                 can only be set when the table is created.",
+                column.name,
+            )));
+        }
         return do_add_auto_generated_column(conn, persistence, source, table, column);
     }
-    // SQLite's `ALTER TABLE ADD COLUMN` cannot express `UNIQUE`,
+    // SQLite's `ALTER TABLE ADD COLUMN` cannot express `UNIQUE`
-    // and a `NOT NULL` column added that way must carry a
+    // or `CHECK`, and a `NOT NULL` column added that way must
-    // default — both route through the rebuild primitive
+    // carry a default — all route through the rebuild
-    // instead (ADR-0029 §6).
+    // primitive instead (ADR-0029 §6).
-    if column.unique || (column.not_null && column.default.is_none()) {
+    if column.unique || column.check.is_some() || (column.not_null && column.default.is_none())
+    {
         do_add_constrained_column_via_rebuild(conn, persistence, source, table, column)
     } else {
         do_add_plain_column(conn, persistence, source, table, column)
@@ -2087,6 +2165,7 @@ fn do_add_auto_generated_column(
         primary_key: false,
         unique: true,
         default_sql: None,
+        check: None,
         user_type: Some(ty),
     });
 
@@ -2233,18 +2312,21 @@ fn do_add_constrained_column_via_rebuild(
         primary_key: false,
         unique: spec.unique,
         default_sql: default_sql_literal(spec)?,
+        check: None,
         user_type: Some(spec.ty),
     });
+    // The CHECK is compiled against the post-add schema, so it
+    // may reference the new column itself.
+    let check_sql = spec
+        .check
+        .as_ref()
+        .map(|e| compile_check_sql(e, &new_schema));
+    if let Some(last) = new_schema.columns.last_mut() {
+        last.check.clone_from(&check_sql);
+    }
 
     let metadata_updates = |tx: &rusqlite::Transaction<'_>| -> Result<(), DbError> {
-        tx.execute(
+        insert_column_metadata(tx, table, &spec.name, spec.ty, check_sql.as_deref())?;
-            &format!(
-                "INSERT INTO {META_TABLE} (table_name, column_name, user_type) \
-                 VALUES (?1, ?2, ?3);"
-            ),
-            [table, spec.name.as_str(), spec.ty.keyword()],
-        )
-        .map_err(DbError::from_rusqlite)?;
         let changes = Changes {
             schema_dirty: true,
             rewritten_tables: vec![table.to_string()],
@@ -3400,6 +3482,11 @@ struct ReadColumn {
     /// literal, echoed verbatim by `schema_to_ddl` so the
     /// rebuild dance preserves it (ADR-0029).
     default_sql: Option<String>,
+    /// The column's `CHECK` constraint in compiled-SQL form
+    /// (ADR-0029 §7), read from the `check_expr` metadata
+    /// column — `pragma_table_info` does not expose CHECK.
+    /// Echoed verbatim by `schema_to_ddl`.
+    check: Option<String>,
     user_type: Option<Type>,
 }
 
@@ -3416,7 +3503,8 @@ fn read_schema(conn: &Connection, table: &str) -> Result<ReadSchema, DbError> {
     // Columns + PK from pragma_table_info, joined with our user-type metadata.
     let mut col_stmt = conn
         .prepare(&format!(
-            "SELECT pti.name, pti.type, pti.\"notnull\", pti.pk, m.user_type, pti.dflt_value \
+            "SELECT pti.name, pti.type, pti.\"notnull\", pti.pk, m.user_type, \
+                    pti.dflt_value, m.check_expr \
              FROM pragma_table_info(?1) AS pti \
              LEFT JOIN {META_TABLE} AS m \
                ON m.table_name = ?1 AND m.column_name = pti.name \
@@ -3434,6 +3522,7 @@ fn read_schema(conn: &Connection, table: &str) -> Result<ReadSchema, DbError> {
                 primary_key: row.get::<_, i64>(3)? != 0,
                 unique: false, // filled in below from pragma_index_list
                 default_sql: row.get(5)?,
+                check: row.get(6)?,
                 user_type,
             })
         })
@@ -3656,6 +3745,13 @@ fn schema_to_ddl(table: &str, schema: &ReadSchema) -> String {
             clause.push_str(" DEFAULT ");
             clause.push_str(default_sql);
         }
+        // ADR-0029 CHECK — echoed verbatim from the compiled
+        // SQL stored in the `check_expr` metadata column.
+        if let Some(check) = &col.check {
+            clause.push_str(" CHECK (");
+            clause.push_str(check);
+            clause.push(')');
+        }
         clauses.push(clause);
     }
 
@@ -3907,6 +4003,7 @@ fn do_add_relationship(
             primary_key: false,
             unique: false,
             default_sql: None,
+            check: None,
             user_type: Some(expected_child_type),
         });
     } else {
@@ -4281,6 +4378,7 @@ fn do_describe_table(conn: &Connection, name: &str) -> Result<TableDescription,
             primary_key: c.primary_key,
             unique: c.unique,
             default: c.default_sql.clone(),
+            check: c.check.clone(),
         })
         .collect();
 
@@ -5478,6 +5576,7 @@ fn build_read_schema(table: &TableSchema, relationships: &[RelationshipSchema])
             primary_key: table.primary_key.contains(&c.name),
             unique: c.unique,
             default_sql: c.default.clone(),
+            check: c.check.clone(),
             user_type: Some(c.user_type),
         })
         .collect();
@@ -8695,6 +8794,137 @@ mod tests {
         );
     }
 
+    // --- CHECK constraints (ADR-0029 §4) --------------------
+
+    /// Parse a `create table` DSL string into its db-call parts
+    /// — the way to get a real `Expr` into a `ColumnSpec.check`
+    /// without hand-building the AST.
+    fn parse_create(dsl: &str) -> (String, Vec<ColumnSpec>, Vec<String>) {
+        match crate::dsl::parser::parse_command(dsl).expect("create table parse") {
+            Command::CreateTable {
+                name,
+                columns,
+                primary_key,
+            } => (name, columns, primary_key),
+            other => panic!("expected CreateTable, got {other:?}"),
+        }
+    }
+
+    /// A `ColumnSpec` carrying a `CHECK`, parsed from DSL.
+    fn col_c_check(name: &str, ty: Type, check_dsl: &str) -> ColumnSpec {
+        let (_, columns, _) = parse_create(&format!(
+            "create table __probe with pk {name}({}) check ({check_dsl})",
+            ty.keyword(),
+        ));
+        columns.into_iter().next().expect("one column")
+    }
+
+    #[tokio::test]
+    async fn create_table_check_constraint_is_enforced() {
+        let db = db();
+        let (n, c, pk) = parse_create(
+            "create table Grades with pk grade(text) check (grade in ('A', 'B', 'C'))",
+        );
+        db.create_table(n, c, pk, None).await.unwrap();
+        let insert_grade = |g: &str| {
+            db.insert(
+                "Grades".to_string(),
+                Some(vec!["grade".to_string()]),
+                vec![Value::Text(g.to_string())],
+                None,
+            )
+        };
+        assert!(insert_grade("A").await.is_ok(), "a value the check allows");
+        assert!(
+            insert_grade("Z").await.is_err(),
+            "a value the check forbids is refused",
+        );
+    }
+
+    #[tokio::test]
+    async fn describe_surfaces_the_check_constraint() {
+        let db = db();
+        let (n, c, pk) =
+            parse_create("create table T with pk age(int) check (age >= 0)");
+        db.create_table(n, c, pk, None).await.unwrap();
+        let desc = db.describe_table("T".to_string(), None).await.unwrap();
+        let age = desc.columns.iter().find(|c| c.name == "age").unwrap();
+        let check = age.check.as_deref().expect("age carries a CHECK");
+        assert!(
+            check.contains(">="),
+            "the compiled check SQL is surfaced: {check}",
+        );
+    }
+
+    #[tokio::test]
+    async fn add_column_check_constraint_is_enforced() {
+        let db = db();
+        people_table(&db).await;
+        db.add_column(
+            "People".to_string(),
+            col_c_check("score", Type::Int, "score >= 0"),
+            None,
+        )
+        .await
+        .expect("a CHECK column adds via the rebuild path");
+        let desc = db.describe_table("People".to_string(), None).await.unwrap();
+        assert!(desc.columns.iter().find(|c| c.name == "score").unwrap().check.is_some());
+        // An update that violates the check is refused.
+        let bad = db
+            .update(
+                "People".to_string(),
+                vec![("score".to_string(), Value::Number("-1".to_string()))],
+                parse_filter("update People set score=-1 where id = 1"),
+                None,
+            )
+            .await;
+        assert!(bad.is_err(), "an update violating the CHECK is refused");
+    }
+
+    #[tokio::test]
+    async fn rebuild_preserves_a_check_constraint() {
+        let db = db();
+        let (n, c, pk) =
+            parse_create("create table T with pk code(text) check (code like 'X%')");
+        db.create_table(n, c, pk, None).await.unwrap();
+        db.add_column("T".to_string(), col("note", Type::Int), None)
+            .await
+            .unwrap();
+        // A type change on `note` rebuilds the table; `code`'s
+        // CHECK must survive the round-trip through schema_to_ddl.
+        db.change_column_type(
+            "T".to_string(),
+            "note".to_string(),
+            Type::Decimal,
+            ChangeColumnMode::Default,
+            None,
+        )
+        .await
+        .unwrap();
+        let desc = db.describe_table("T".to_string(), None).await.unwrap();
+        assert!(
+            desc.columns.iter().find(|c| c.name == "code").unwrap().check.is_some(),
+            "code keeps its CHECK across the rebuild",
+        );
+    }
+
+    #[tokio::test]
+    async fn add_serial_column_with_a_check_is_refused() {
+        let db = db();
+        people_table(&db).await;
+        let result = db
+            .add_column(
+                "People".to_string(),
+                col_c_check("seq", Type::Serial, "seq > 0"),
+                None,
+            )
+            .await;
+        assert!(
+            result.is_err(),
+            "a CHECK on an auto-generated column is a create-table-only feature",
+        );
+    }
+
     #[tokio::test]
     async fn update_with_all_rows_affects_everything() {
         let db = db();
@@ -8966,6 +9196,7 @@ mod tests {
                     primary_key: true,
                     unique: false,
                     default_sql: None,
+                    check: None,
                     user_type: Some(Type::Serial),
                 },
                 ReadColumn {
@@ -8975,6 +9206,7 @@ mod tests {
                     primary_key: false,
                     unique: true,
                     default_sql: None,
+                    check: None,
                     user_type: Some(Type::Text),
                 },
             ],

src/dsl/grammar/ddl.rs

@@ -13,7 +13,7 @@
 
 use crate::dsl::action::ReferentialAction;
 use crate::dsl::command::{
-    ChangeColumnMode, ColumnSpec, Command, IndexSelector, RelationshipSelector,
+    ChangeColumnMode, ColumnSpec, Command, Expr, IndexSelector, RelationshipSelector,
 };
 use crate::dsl::value::Value;
 use crate::dsl::grammar::{
@@ -27,7 +27,7 @@ use crate::dsl::grammar::{
 /// candidates (ADR-0024 §HintMode-per-node).
 const NEW_NAME_HINT: HintMode = HintMode::ForceProse("hint.ambient_typing_name");
 use crate::dsl::types::Type;
-use crate::dsl::walker::outcome::{MatchedKind, MatchedPath};
+use crate::dsl::walker::outcome::{MatchedItem, MatchedKind, MatchedPath};
 
 // =================================================================
 // Building blocks
@@ -616,7 +616,8 @@ fn build_add(path: &MatchedPath) -> Result<Command, ValidationError> {
                     message_key: "parse.error_wrapper",
                     args: vec![("detail", "unknown type".to_string())],
                 })?;
-            let (not_null, unique, default) = collect_column_constraints(path)?;
+            let (not_null, unique, default, check) =
+                collect_column_constraints(path)?;
             Ok(Command::AddColumn {
                 table: require_ident(path, "table_name")?,
                 column: require_ident(path, "column_name")?,
@@ -624,8 +625,7 @@ fn build_add(path: &MatchedPath) -> Result<Command, ValidationError> {
                 not_null,
                 unique,
                 default,
-                // CHECK joins in a later ADR-0029 step.
+                check,
-                check: None,
             })
         }
         Some("1") => build_add_relationship(path),
@@ -842,8 +842,20 @@ const DEFAULT_CONSTRAINT_NODES: &[Node] = &[
 ];
 const DEFAULT_CONSTRAINT: Node = Node::Seq(DEFAULT_CONSTRAINT_NODES);
 
+// `check ( <expr> )` — the expression is the ADR-0026 WHERE
+// grammar, reached through `Subgrammar` (ADR-0029 §2.1). The
+// parentheses match SQL's `CHECK (…)` and give the parser an
+// unambiguous end for the expression.
+const CHECK_CONSTRAINT_NODES: &[Node] = &[
+    Node::Word(Word::keyword("check")),
+    Node::Punct('('),
+    Node::Subgrammar(&super::expr::OR_EXPR),
+    Node::Punct(')'),
+];
+const CHECK_CONSTRAINT: Node = Node::Seq(CHECK_CONSTRAINT_NODES);
+
 const COLUMN_CONSTRAINT_CHOICES: &[Node] =
-    &[NOT_NULL_CONSTRAINT, UNIQUE_CONSTRAINT, DEFAULT_CONSTRAINT];
+    &[NOT_NULL_CONSTRAINT, UNIQUE_CONSTRAINT, DEFAULT_CONSTRAINT, CHECK_CONSTRAINT];
 const COLUMN_CONSTRAINT: Node = Node::Choice(COLUMN_CONSTRAINT_CHOICES);
 
 /// Zero-or-more constraints — the suffix after a column's
@@ -894,18 +906,49 @@ const CREATE_TABLE_NODES: &[Node] = &[
 ];
 const CREATE_TABLE: Node = Node::Seq(CREATE_TABLE_NODES);
 
+/// Consume a `check` constraint's `( <expr> )` from `items`,
+/// which must be positioned just after the `Word("check")`,
+/// and build the ADR-0026 expression (ADR-0029 §2.1). The
+/// grammar's `Seq` guarantees the surrounding `(` … `)`;
+/// paren depth handles a parenthesised sub-expression inside.
+fn consume_check_expr(
+    items: &mut std::iter::Peekable<std::slice::Iter<'_, MatchedItem>>,
+) -> Result<Expr, ValidationError> {
+    items.next(); // the opening `(`
+    let mut depth = 1usize;
+    let mut expr_items: Vec<MatchedItem> = Vec::new();
+    for inner in items.by_ref() {
+        match &inner.kind {
+            MatchedKind::Punct('(') => {
+                depth += 1;
+                expr_items.push(inner.clone());
+            }
+            MatchedKind::Punct(')') => {
+                depth -= 1;
+                if depth == 0 {
+                    break;
+                }
+                expr_items.push(inner.clone());
+            }
+            _ => expr_items.push(inner.clone()),
+        }
+    }
+    super::expr::build_expr(&expr_items)
+}
+
 /// Collect the ADR-0029 constraint suffix from a
 /// single-column command's matched path (`add column`),
-/// returning the `(not_null, unique, default)` triple. The
+/// returning the `(not_null, unique, default, check)` tuple.
-/// scan reacts only to the four constraint keywords, so
+/// The scan reacts only to the constraint keywords, so
 /// passing the whole path is safe. (`create table`'s
 /// multi-column collection is inline in `build_create_table`.)
 fn collect_column_constraints(
     path: &MatchedPath,
-) -> Result<(bool, bool, Option<Value>), ValidationError> {
+) -> Result<(bool, bool, Option<Value>, Option<Expr>), ValidationError> {
     let mut not_null = false;
     let mut unique = false;
     let mut default = None;
+    let mut check = None;
     let mut items = path.items.iter().peekable();
     while let Some(item) = items.next() {
         match &item.kind {
@@ -929,10 +972,13 @@ fn collect_column_constraints(
                     })?;
                 default = Some(value);
             }
+            MatchedKind::Word("check") => {
+                check = Some(consume_check_expr(&mut items)?);
+            }
             _ => {}
         }
     }
-    Ok((not_null, unique, default))
+    Ok((not_null, unique, default, check))
 }
 
 /// The friendly error for declaring a constraint a
@@ -1005,6 +1051,13 @@ fn build_create_table(path: &MatchedPath) -> Result<Command, ValidationError> {
                     last.default = Some(value);
                 }
             }
+            // `check ( <expr> )` (ADR-0029 §2.1).
+            MatchedKind::Word("check") => {
+                let expr = consume_check_expr(&mut items)?;
+                if let Some(last) = columns.last_mut() {
+                    last.check = Some(expr);
+                }
+            }
             _ => {}
         }
     }
@@ -1152,4 +1205,33 @@ mod constraint_tests {
             other => panic!("expected AddColumn, got {other:?}"),
         }
     }
+
+    #[test]
+    fn create_table_parses_a_check_constraint() {
+        let cols = create_columns("create table T with pk age(int) check (age >= 0)");
+        assert_eq!(cols.len(), 1);
+        assert!(cols[0].check.is_some(), "the column carries a CHECK");
+    }
+
+    #[test]
+    fn add_column_parses_a_check_constraint() {
+        match parse_command("add column to T: age (int) check (age >= 0 and age < 150)")
+            .expect("parse")
+        {
+            Command::AddColumn { check, .. } => {
+                assert!(check.is_some(), "the column carries a CHECK");
+            }
+            other => panic!("expected AddColumn, got {other:?}"),
+        }
+    }
+
+    #[test]
+    fn check_with_a_parenthesised_sub_expression_parses() {
+        // The check's own parens plus a nested group — the
+        // builder's paren-depth scan must pair them correctly.
+        let cols = create_columns(
+            "create table T with pk n(int) check ((n > 0) or (n < -10))",
+        );
+        assert!(cols[0].check.is_some());
+    }
 }

src/output_render.rs

@@ -369,6 +369,9 @@ fn constraints_display(c: &ColumnDescription) -> String {
     if let Some(default) = &c.default {
         parts.push(format!("DEFAULT {default}"));
     }
+    if let Some(check) = &c.check {
+        parts.push(format!("CHECK ({check})"));
+    }
     parts.join(", ")
 }
 
@@ -521,6 +524,7 @@ mod tests {
             primary_key: pk,
             unique: false,
             default: None,
+            check: None,
         }
     }
 
@@ -990,6 +994,7 @@ mod tests {
                 primary_key: false,
                 unique: false,
                 default: None,
+                check: None,
             }],
             outbound_relationships: Vec::new(),
             inbound_relationships: Vec::new(),

src/persistence/csv_io.rs

@@ -376,6 +376,7 @@ mod tests {
             unique: false,
             not_null: false,
             default: None,
+            check: None,
         }
     }
 

src/persistence/mod.rs

@@ -152,6 +152,10 @@ pub struct ColumnSchema {
     /// form SQLite reports and `schema_to_ddl` echoes verbatim.
     /// `None` when the column has no default.
     pub default: Option<String>,
+    /// `CHECK` constraint in compiled-SQL form (ADR-0029 §7),
+    /// echoed verbatim into the rebuilt DDL. `None` when the
+    /// column has no check.
+    pub check: Option<String>,
 }
 
 /// One index as recorded in `project.yaml` (ADR-0025).
@@ -383,6 +387,7 @@ mod tests {
                 unique: false,
                 not_null: false,
                 default: None,
+                check: None,
             }],
             rows: vec![vec![CellValue::Text("Alice".to_string())]],
         };

src/persistence/yaml.rs

@@ -129,6 +129,10 @@ fn write_column(out: &mut String, col: &ColumnSchema) {
         line.push_str(", default: ");
         line.push_str(&yaml_string(default));
     }
+    if let Some(check) = &col.check {
+        line.push_str(", check: ");
+        line.push_str(&yaml_string(check));
+    }
     line.push_str(" }");
     let _ = writeln!(out, "{line}");
 }
@@ -238,6 +242,7 @@ pub(crate) fn parse_schema(body: &str) -> Result<SchemaSnapshot, YamlError> {
                 unique: c.unique,
                 not_null: c.not_null,
                 default: c.default,
+                check: c.check,
             });
         }
         tables.push(TableSchema {
@@ -370,6 +375,9 @@ struct RawColumn {
     /// `DEFAULT` SQL literal (ADR-0029); absent in older files.
     #[serde(default)]
     default: Option<String>,
+    /// `CHECK` SQL (ADR-0029); absent in older files.
+    #[serde(default)]
+    check: Option<String>,
 }
 
 #[derive(Deserialize)]
@@ -407,16 +415,16 @@ mod tests {
                     name: "Customers".to_string(),
                     primary_key: vec!["id".to_string()],
                     columns: vec![
-                        ColumnSchema { name: "id".to_string(), user_type: Type::Serial, unique: false, not_null: false, default: None },
+                        ColumnSchema { name: "id".to_string(), user_type: Type::Serial, unique: false, not_null: false, default: None, check: None },
-                        ColumnSchema { name: "Name".to_string(), user_type: Type::Text, unique: false, not_null: false, default: None },
+                        ColumnSchema { name: "Name".to_string(), user_type: Type::Text, unique: false, not_null: false, default: None, check: None },
                     ],
                 },
                 TableSchema {
                     name: "Orders".to_string(),
                     primary_key: vec!["id".to_string()],
                     columns: vec![
-                        ColumnSchema { name: "id".to_string(), user_type: Type::Serial, unique: false, not_null: false, default: None },
+                        ColumnSchema { name: "id".to_string(), user_type: Type::Serial, unique: false, not_null: false, default: None, check: None },
-                        ColumnSchema { name: "CustId".to_string(), user_type: Type::Int, unique: false, not_null: false, default: None },
+                        ColumnSchema { name: "CustId".to_string(), user_type: Type::Int, unique: false, not_null: false, default: None, check: None },
                     ],
                 },
             ],
@@ -484,6 +492,7 @@ mod tests {
                     unique: false,
                     not_null: false,
                     default: None,
+                    check: None,
                 }],
             }],
             relationships: vec![],
@@ -523,6 +532,7 @@ mod tests {
                         unique: false,
                         not_null: false,
                         default: None,
+                        check: None,
                     },
                     ColumnSchema {
                         name: "title".to_string(),
@@ -530,6 +540,7 @@ mod tests {
                         unique: true,
                         not_null: true,
                         default: Some("'untitled'".to_string()),
+                        check: None,
                     },
                     ColumnSchema {
                         name: "stock".to_string(),
@@ -537,6 +548,7 @@ mod tests {
                         unique: false,
                         not_null: false,
                         default: Some("0".to_string()),
+                        check: Some("\"stock\" >= 0".to_string()),
                     },
                 ],
             }],
@@ -622,8 +634,8 @@ relationships:
                 name: "Items".to_string(),
                 primary_key: vec!["a".to_string(), "b".to_string()],
                 columns: vec![
-                    ColumnSchema { name: "a".to_string(), user_type: Type::Int, unique: false, not_null: false, default: None },
+                    ColumnSchema { name: "a".to_string(), user_type: Type::Int, unique: false, not_null: false, default: None, check: None },
-                    ColumnSchema { name: "b".to_string(), user_type: Type::Int, unique: false, not_null: false, default: None },
+                    ColumnSchema { name: "b".to_string(), user_type: Type::Int, unique: false, not_null: false, default: None, check: None },
                 ],
             }],
             relationships: vec![],

src/ui.rs

@@ -1117,6 +1117,7 @@ mod tests {
                     primary_key: true,
                     unique: false,
                     default: None,
+                    check: None,
                 },
                 ColumnDescription {
                     name: "Name".to_string(),
@@ -1126,6 +1127,7 @@ mod tests {
                     primary_key: false,
                     unique: false,
                     default: None,
+                    check: None,
                 },
             ],
             outbound_relationships: Vec::new(),

tests/walking_skeleton.rs

@@ -252,6 +252,7 @@ fn fake_table(name: &str, columns: &[(&str, Type, bool)]) -> TableDescription {
                 primary_key: *pk,
                 unique: false,
                 default: None,
+                check: None,
             })
             .collect(),
         outbound_relationships: Vec::new(),
@@ -419,6 +420,7 @@ fn add_relationship_flow_shows_parent_side_with_inbound_section() {
             primary_key: true,
             unique: false,
             default: None,
+            check: None,
         }],
         outbound_relationships: Vec::new(),
         inbound_relationships: vec![RelationshipEnd {
@@ -470,6 +472,7 @@ fn add_relationship_flow_shows_inbound_section_on_parent() {
             primary_key: true,
             unique: false,
             default: None,
+            check: None,
         }],
         outbound_relationships: Vec::new(),
         inbound_relationships: vec![RelationshipEnd {