A cross-field typeguard guard passes the DEFAULT gate at declaration and fails at every insert

[farhan-syah]

A typeguard DEFAULT or VALUE clause is a generated-column expression, evaluated per row against the document. A column DEFAULT is a constant expression, const-folded once.

CREATE TYPEGUARD validates its clauses against the column-DEFAULT gate. A cross-field expression parses there, so declaration succeeds. CONVERT COLLECTION then copies it onto a strict-schema column, where the column-DEFAULT evaluator const-folds it and raises UnevaluableDefault on every insert.

Reproduction

CREATE COLLECTION t (id TEXT PRIMARY KEY, status TEXT, lowered TEXT);
CREATE TYPEGUARD ON t (lowered STRING VALUE LOWER(status));
CONVERT COLLECTION t TO document_strict (id TEXT, status TEXT, lowered TEXT);
INSERT INTO t (id, status) VALUES ('k1', 'ACTIVE');

The insert fails. The declaration reported no error.

Expected

Either the guard evaluates per row after conversion, keeping the semantics it had before, or CONVERT refuses to carry a guard whose expression references another column and says so.

Notes

Catching this at CONVERT needs nodedb-sql to expose whether a classified DEFAULT references a column. A second classifier must not be written for it.

There is a related semantic narrowing at the same site, documented in code: a guard VALUE expr always overwrites, while a strict-schema column DEFAULT fills only when the column is omitted. Strict schema has one materialization slot, so the conversion cannot preserve both meanings.

[EnRaiha]

Grouping note for the record: the resubmission PR for this issue carries three defects on the same declaration path.

1. The filed defect: a cross-field guard (VALUE LOWER(status)) carried onto a strict column DEFAULT is refused at CONVERT, naming field and clause.
2. Typeguard handlers resolving DatabaseId::DEFAULT instead of the session database.
3. CONVERT dropping the source primary key (and a column list that omits it being refused).

Defects 2 and 3 are prerequisites of the same gate and travel with this PR rather than in separate ones; the maintainer's resubmission conditions grouped them under this issue (typeguard database_id threading, CONVERT primary-key carry, cross-column refusal).