Following @benno's tip on !86 (closed), I'm creating separate merge requests for separate topics. In this case, I add two commits as one builds off the other:
ɔ, which I couldn't find anywhere in Compose.pre. This adds new symbols.
<dead_hook> to write
ɚ if your keyboard layout doesn't allow for
All the symbols above are used in the IPA, as can be seen in the commit messages. (Links point to Wikipedia, but it should be easy to find other examples of use of these symbols anywhere.)