maybe I'm missing something in what you're saying here, but I don't see how merely checking "inCompose" would work with the STR in my comment https://github.com/mozilla-b2g/gaia/pull/16798#discussion_r10382438 above:
* the "main" instance is in a composer view (because the user was there before starting the activity)
* the "activity" instance is also in a composer view (obviously)
* we need to change the panel only for the "activity" instance

Do I miss something?