During the validation process for missing keys, we should implement two additional checks:

If the document indicates that the index should be marked as multi-key (shouldMarkIndexAsMultikey), but the index is not a multi-key index (isMultikey), we should generate an error.
If the index is marked as multi-key, but the multi-key paths (getMultikeyPaths) do not cover (covers) the record key, we should generate an error.

For checking extra keys, no further modifications are necessary as it should function as designed.

Additionally, we will add a test to ensure it is working as expected.