Two sources, tried in order, and the response always says which one answered:
  - `source="pubchem"`  — the curated, human-checked IUPAC name. Authoritative,
    but only exists for compounds PubChem indexes.
  - `source="openclatura"` — a name constructed from the molecular graph by a
    deterministic IUPAC Blue Book (2013) rule engine. Works on any valid
    structure, including novel compounds, intermediates and analogues.

Parameters:
  prefer_pubchem — check PubChem first (default true). Set false to force
    generation, or to keep the call purely offline and ~100x faster: the
    rule engine takes ~5 ms, the PubChem round-trip 0.6-1 s.
  explain — also return `rules_hit`, the Blue Book rules that fired
    (e.g. P-44, P-61). Costs ~5x the naming time; off by default.
  verify — round-trip the generated name through OPSIN and report whether it
    parses back to the same structure. Needs a Java runtime; without one the
    result reports `verification="skipped_no_java"` instead of failing.

Returns: `{name, smiles, source, generated, engine}` (+ `rules_hit`,
`verification` when requested), or `{error, smiles}`.

A generated name is a systematic construction, not a database record —
treat `generated=true` accordingly.