broken UI in reply to a thread in commit view

Summary

There is a broken UI in the commit view when replying to a started thread (Screenshot below).

Steps to reproduce

  1. go to a commit detail page
  2. open a new thread/discussion
  3. click in the reply field
expected result actual result
Screenshot_2019-06-14_at_10.01.32 Screenshot_2019-06-14_at_09.12.57

Possible fixes

the markup for the thread/discussion reply is not correct. Several elements are missing which are important for rendering it correctly.