A file being imported is not necessarily one this reader wrote. Extracts the
record validator so both the store read and the import path share it, and covers
what it has to guarantee: a partly-corrupt file costs the reader only the broken
records, a hue that is not a hex colour never reaches a style attribute, an
export written before F13 is a file with nothing of its own rather than an
error, and an event whose dates contradict themselves does not land.
Co-Authored-By: Claude Opus 5 (1M context) <[email protected]>
