Breaking for 0.x: Search computes InChIKey, formula and mass from the
structure; strict also refuses contested queries; n_source_support no
longer counts echoed (derived) records, and DTXSID queries are
cross-checked through CompTox's CAS number; ClassyFire is removed. Cuts
the [Unreleased] section: the structure QC from the 630-CAS audit
(plans/2026-10-13-structure-qc-chebi-smiles.md).

Whole suite: 1,689 passed, 34 skipped; doctests 490 passed, 80 skipped;
strict docs build passes; uv build: wheel 3.3 MB, sdist 4.1 MB, no
databases.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>