Suggestion

#6240 shows an example of a PR where changes in one package are given unit test coverage by changes in another package. Is that something we want factored into the codecov reports? At first I wanted it, but now I'm wondering if we should consider coverage just from within each package's own unit tests...

If we do want this, from @RebeccaStevens's #6240 (comment):

Codecov can merge multiple reports. I've already set this up in ts-api-utils to merge the reports from different TypeScript versions.

See https://docs.codecov.com/docs/flags for more details on how it works.