Signature
Description
Sets, updates, or removes an extra-metadata entry. An emptyvalue removes the
entry. Emits ExtraMetadataUpdated.
Dev: Reverts with AccessControlUnauthorizedAccount when the caller does not hold METADATA_ROLE.
Dev: Reverts with InvalidMetadataKey when key is the empty string.
Param: key Metadata entry key (e.g. "category").
Param: value New value, or empty string to remove.
Access control
METADATA_ROLE gates this call.