Define GET /reference/{id}/bases in favor of GAReference.sequence.

This approach is intended to allow for more efficient access to the bases needed by the client. Returning an upwards of 300MB (uncompressed) string as a single JSON value would likely have performance issues; this is solved here via pagination if the endpoint chooses to implement the method with multiple pages.
Thanks, that's an unfortunate quirk. On further thought, it doesn't make sense to allow this field to be null so I've removed the union type. I've the 'end' coordinate nullable, let me know if you feel this is too asymmetric.

Note: SearchReads may suffer from the original issue you described.