A GM can start a contest but there's no way to continue it, or for the player of that character to continue it.
The system expects only players to use character abilities. A GM should not be able to start an ability, and/or it should provide a helpful error message that only players can start contest.
Possibility to investigate: can ownership of a chat message be automatically reassigned to the player of the originating character sheet (if any player owns the character)?
A GM can start a contest but there's no way to continue it, or for the player of that character to continue it.
The system expects only players to use character abilities. A GM should not be able to start an ability, and/or it should provide a helpful error message that only players can start contest.