Do I understand correctly?
a) This is available via GitHub actions: plugins with proper specs / tests using GitHub actions will have a badge on GitHub, if all tests pass and the status of CI actions is readable by API.
b) Except discourse official plugins and pavilion plugins, there exist no automatic overview for administrators, if used plugins will work in the version intended for update?
Searching for metadata on plugin compatibility, I found Introducing .discourse-compatibility: pinned plugin/theme versions for older Discourse versions via a .discourse-compatibility file.
As I understand, this is a solution to the reverse problem: discourse to old for a plugin.
How to treat the other way around: plugin to old for discourse?
Could /admin/upgrade warn about plugins, failing tests for an intended upgrade?