Nice! Haven't played with it yet, but tightening up the types allowed for hooks is a good thing. This will make the documentation even easier, as there are fewer corner-cases to have to explain.

Question 1: Is it possible to restrict env_change a bit more to require a hashmap of vecs?

Question 2:

I was even thinking last night about preloading env_change with an empty PWD record. That would allow "out-of-the-box":

$env.config.hooks.env_change.PWD ++= [{print (ls | grid -c -i)}]
$env.config.hooks.env_change.PWD ++= [{process-env-file}]

Today, you first have to check if PWD exists or not.

Of course, that doesn't solve the problem for other environment variables, but I think PWD is so common that it might deserve a convenience default-value?

What is the status on this one, if I remember we talked about it briefly two meetings ago and said we like it as soon as the technical side is good to got?