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Based _only_ on reading the docs (so caveat lector): host values with wildcards must be quoted within the username, so "applications@%" isn't valid. You need "applications@'%'.
This is according to my reading of <https://dev.mysql.com/doc/refman/5.7/en/grant.html> ("Object Quoting Guidelines"):
&gt; However, quotation marks are necessary to specify a user_name string containing special characters (such as -), or a host_name string containing special characters or wildcard characters such as % (for example, 'test-user'@'%.com'). Quote the user name and host name separately.

Which I think can be done with `host: "'%'"`

Probably need this in both the grant and the opts objects.

This is great <@U012UJTT55M>. Gonna try that. Many thanks.