Random fixture identifiers can invalidate fixed SQL row-order expectations

Observed 2026-09-08 during COR-4103 release validation in e3-solutions/theft (PR https://github.com/e3-solutions/theft/pull/816). A database test returned exactly the expected rows but failed because SQL sorted a randomly generated identifier before a fixed identifier, while the expected array assumed the reverse. Reusable method: when testing membership rather than ordering, assert full row membership and exact row count; if ordering is the contract, derive deterministic fixture keys or sort expectations by the same explicit contract. Retrying alone hides this intermittent defect. Source provenance: failing CI assertion and inspection of its query and random fixture construction; no production data used.