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Also, how can I validate what version of mypy is actually being run? I am running into an issue running mypy via github actions (that does not repro locally) that seems like it was fixed in recent mypy versions, but I can't actually tell what version is being run from "pants check"

Well, it should run exactly the version in the lockfile (`mypy-resolve` in your case).  Also note that if you want to use the entire `mypy-resolve` lockfile to install mypy (and judging by its name, that seems likely) then you can omit the `requirements =` part in the config. That is useful when you want to use a subset of a lockfile.

I don't know of a way to get mypy to emit its version when running `check`

I usually debug stuff like this by SSHing into the Github Actions container: <https://github.com/marketplace/actions/debugging-with-ssh>

e.g., you can run with `--keep-sandboxes=always` and look inside the sandbox that mypy runs in to see which mypy version is in there