In MariaDB the UNTIL keyword is inclusive.
"The replica will start replication from the current GTID position, run up to and including the event with the GTID specified, and then stop. "
Keyword UNTIL origin is form imperative languages, where UNTIL is the end condition of a loop.
Depending from the position of the counter (before or after reply), the UNTIL condition will be processed or not.
SQL is a declarative language, so the counter position in the loop is hidden, so maybe UNTIL is different implemented in different databases (if used in an SQL-statement, not procedures). Procedures are also based on imperative paradigm.
So I suggest to add keywords EXCLUSIVE and INCLUSIVE.
The default would be INCLUSIVE, which is the current MariaDB behaviour.