Hello 
I’ve been thinking about this a lot, and I added three configurable options:
- None: no additional dismiss gesture
- Grip: a visual grip is shown in the footer
- Gesture: the modal can be dismissed by swiping down when at the top, or swiping up when at the bottom. The native Back gesture/button also dismisses the modal on mobile.
I tried to make it work somewhat like Facebook’s comment modals.
The most interesting part is the native Back handling. Rather than navigating away from the underlying topic list, the modal consumes the Back action and closes itself, while keeping the user’s position in the list.