My mistake, it’s called
gameprop(). It’s also used in Options.dinky.
You need to call
gameprop( "sayLineForever", true) before the sayLine happens, which means it’s too late by the time you get the callback. This should be set once (probably in boot.dinky) if you have talkies.
This is all kind of a kludge, if I was doing this “for real”, talking would be built into the system (because of lipsync, etc).