But once we grant permission to the audio-capture permission for a contextual request, I would expect the permissions API to return back that 'Ask' would still be present, as we did not remember my decision with the gUM audio request & because we don't persist session permissions for gUM audio requests.

The easiest way to prove or disprove my point is to rebase the patch against the latest gaia & re-run this test. I could be misinterpreting the what navigator.mozPermissionSettings.get does here, but it can easily be double checked against the latest gaia changes that include Fred's patch for removing the remember my choice option.