There is no such message.
Instead of polling, why not just check the active sequence, before doing anything?
the intention is to populate a read-only textfield with the sequence name for the purpose of cross-checking, before the user hits the export button next to said text field, which will trigger a custom export process. I want to circumvent having an "update" button, or use panel focus/click events, that's always one click more than necessary. The ideal solution would be to have non-blocking events, alternatively I prbably would have to use an interval-based poll, but only when the panel is visible to the user. I think there is a switch for this...correct? To check if a panel is active (not focused, but visible in the GUI)?
Yes, you can tell if an extension is open or not; see CEP HTML Test Extension.
Perhaps your panel could enable/disable the export button, after confirming whether the current active sequence is the same as the previously noticed active sequence?
Okay, so there is (currently) no way to "know" programmatically if the
panel is visible, just open or closed.
I was also thinking about pausing the interval timer whenever PPro is
"idle", i.e. not playing back, mouse button is pressed etc., basically
excluding "global" states that might be disturbed by a timed blocking
method. Do you reckon this is feasible, because the "exclusion list" might
be quite vast?
We don't recommend interval timers, at all.
I'd recommend checking the active sequence immediately after the user clicks that button, and fail out if the current sequence is incorrect.