Comment-or-update-comment

[JasonEtco]

Not really an app idea, but I think a lot of apps will want to post a comment on a PR/issue then update that comment on subsequent events (rather than posting a new comment). As an example, Codecov has this behavior; it's kind of a pain to write all of that manually, since its very boilerplate-y. It could use the APP_ID and metadata to mark a comment as belonging to the app.