Too-long `elm.json` `"summary"` is reported as invalid package name

I tried to install a package on a new project and got this error:

-- INVALID ELM.JSON ------------------------------------------------------------

A valid package name look like "author/project"

The "name" in my elm.json looked fine, so I wasn't sure what the problem was. I then tried to install the same package with the elm executable and got this error:

-- SUMMARY TOO LONG --------------------------------------------------- elm.json

I got stuck while reading your elm.json file. Your "summary" is too long:

...

I need it to be under 80 bytes so it renders nicely on the package website!

Note: I count the length in bytes, so using non-ASCII characters costs extra.
Please report your case at https://github.com/elm/compiler/issues if this seems
overly restrictive for your needs.

It actually seems like this happens for other parsing errors in elm.json too, e.g. for the lack of a "license" attribute.