I wish we could make the diagnostics here a bit friendlier. Some users may not be aware of how the semantics of __init_subclass__ work, and the diagnostic doesn't try to explain it much at the moment:

But propagating context into (or out of) binding.report_diagnostics() in order to add subdiagnostics looks really complicated ☹️. So that's probably better done as a followup

Originally posted by @AlexWaygood in astral-sh/ruff#22185 (review)