enforceMetadataLimits(metadata: Record<string, string>,maxValueLength: number,maxEntries?: number,): Record<string, string>
Only the fields that grow with what the buyer selected can realistically exceed the per-value limit. Form validation already holds every other field well below the smallest provider limit of 255.
thank_you_url is deliberately NOT handled here. It must never fail a
checkout, so an over-cap URL is dropped before signing, in
buildItemsMetadata. A cap here, after signPrice, would strip a key the
proof covers, and the webhook would read the session as tampered.