Validate Code

Validate and describe one or more Combined Nomenclature customs codes.

Single code: normalises loose input, resolves the hierarchy of description levels in lang, and returns {code, levels, product_name, has_subcodes} plus interpreted_from when the input was reformatted. The synthetic 'TOTAL' aggregate short-circuits the nomenclature lookup. Comma-separated input is treated as a batch (strict digits-only regex, at most 50 codes) and returns {"results": [...]}, each item a success dict or {"code", "error": {"status", "detail"}}.

Errors: 400 (malformed/too short), 404 (unknown code, with the nearest valid parent), 503 (nomenclature service unavailable). A mostly-numeric string over 12 digits with no commas is rejected as a likely pasted list. Successful responses are day-cacheable.