When there's an error while generating checks it results in local logging to the console, but no persistent logging. This means we don't have any visibility into what checks are experiencing errors, outside of when a developer is paying attention to a specific pageload.
This would be useful in general for knowing about edge cases that cause unexpected issues, and would have resulted in us detecting issues like T418173 much more quickly.
Because of the architecture of editcheck, where we're constantly regenerating the list of checks, suggestions are likely to produce a lot of repeat errors if we individually logged each error. As such, it would probably be best to track "edit sessions in which errors occurred" rather than absolute error counts.
I thus propose that we track a counter, which is incremented once in each session where errors of a check type are seen. Naming would be stats.mediawiki_editcheck_errors_total with a payload of {kind: '[check-name]'}. (Or something equivalent -- I need to double-check what we can easily summarize together, since I presume we'd want this on our dashboard.)
