feat: ADR-0035 4a.2 — per-column CHECK/DEFAULT + composite UNIQUE

Advanced-mode SQL CREATE TABLE gains the constraints that need no new
internal table (the 4a.2 slice):

- Grammar (sql_create_table.rs): column-level DEFAULT/CHECK and
  table-level UNIQUE(cols). DEFAULT is a literal or a *parenthesised*
  expression (standard SQL) — a bare sql_expr greedily eats a following
  NOT (NOT IN/LIKE/BETWEEN), breaking `DEFAULT 0 NOT NULL`; the parens
  bound it. CHECK is paren-bounded already.
- Builder (ddl.rs): captures CHECK/DEFAULT raw SQL text by byte span
  (sql_expr builds no AST) via capture_parenthesised_span /
  capture_expr_span; routes single-column table UNIQUE into the
  column's flag and composite UNIQUE into unique_constraints.
- Command/worker: ColumnSpec gains check_sql/default_sql (raw, preferred
  over the typed Expr/Value); Command::SqlCreateTable + Request +
  do_create_table gain unique_constraints; do_create_table emits raw
  CHECK/DEFAULT and composite UNIQUE clauses.
- Round-trip (part D): ReadSchema/TableSchema gain unique_constraints;
  read_schema detects composite UNIQUE via PRAGMA index_list origin 'u'
  (single-column still folds to the column flag); schema_to_ddl emits
  them; YAML RawTable/write_table round-trips (optional-on-read).
  CHECK round-trips via __rdbms_playground_columns.check_expr, DEFAULT
  via PRAGMA table_info — no new metadata table.

Table-level/multi-column CHECK remains 4a.3 (rejected "not yet
supported"); FK is 4b.

Tests: +7 builder (raw-text capture incl. the DEFAULT 0 NOT NULL
boundary the fix was found by; single/composite UNIQUE routing) and +4
Tier-3 (CHECK enforced, DEFAULT applied, composite UNIQUE enforced, and
all three survive a rebuild — the part-D round-trip). 1752 pass / 0 fail
/ 1 ignored; clippy clean. Plan + requirements.md updated.

docs/plans/20260525-adr-0035-sql-ddl-4a2.md

@@ -71,10 +71,17 @@ CHECK). Builds directly on the 4a `SqlCreateTable` command + grammar.
 ### 4.1 Grammar (`src/dsl/grammar/sql_create_table.rs`)
 
 - **Column constraints** — extend `COL_CONSTRAINT_CHOICES` with:
-  - `DEFAULT <sql_expr>`: `Seq[ Word("default"),
-    Subgrammar(&sql_expr::SQL_OR_EXPR) ]`.
+  - `DEFAULT <value>` where `<value>` is a **literal** (number /
+    string / `null` / `true` / `false`) **or a parenthesised**
+    `( <sql_expr> )` — *not* a bare `sql_expr`. This matches standard
+    SQL (a complex default must be parenthesised) **and** resolves a
+    real ambiguity found in testing: a bare `sql_expr` greedily
+    consumes a following `NOT` (as `NOT IN`/`NOT LIKE`/`NOT BETWEEN`),
+    breaking the common `DEFAULT 0 NOT NULL`. The parens give the
+    expression a clean right edge. (See §6.3.)
   - `CHECK ( <sql_expr> )`: `Seq[ Word("check"), Punct('('),
-    Subgrammar(&sql_expr::SQL_OR_EXPR), Punct(')') ]`.
+    Subgrammar(&sql_expr::SQL_OR_EXPR), Punct(')') ]` — already
+    paren-bounded, so no ambiguity.
 - **Table element** — extend `ELEMENT_CHOICES` with table-level
   `UNIQUE ( col, … )`: `Seq[ Word("unique"), Punct('('),
   Repeated(uniq_column, ',', 1), Punct(')') ]`. (Distinct ident role,
@@ -146,9 +153,13 @@ execution; `finalize_persistence` writes yaml/CSV/journal. No new
    unknown-column `[ERR]`. If they do, the grammar must suppress
    schema-existence checks in the CREATE-TABLE CHECK context (as the
    simple-mode path effectively does). Resolve during step 1.
-2. **DEFAULT expression boundary** — confirm the `sql_expr` match is
-   maximal enough that the raw-text slice for `DEFAULT <expr>` ends
-   cleanly before the next element. Covered by builder tests.
+2. **DEFAULT grammar — resolved during implementation (§4.1).** A bare
+   `DEFAULT <sql_expr>` greedily ate a following `NOT` (start of
+   `NOT IN`/`LIKE`/`BETWEEN`), so `DEFAULT 0 NOT NULL` failed to parse
+   (caught by a builder test). Fixed by restricting a bare default to a
+   **literal**, with complex defaults **parenthesised** (`DEFAULT
+   (expr)`) — standard SQL, and the parens bound the expression. The
+   raw-text capture keeps the parens so it re-emits as valid SQL.
 
 ## 7. Devil's Advocate review of this plan