If you use the git-codereview tool, it automatically rewrites #nnn references on subrepos to golang/go#nnn.

That's true, but it is surprisingly easy to forget to install the git-codereview commit hooks when cloning the subrepos.

I'll put forth the (potentially controversial) opinion that any git-codereview hook fix/error should have a corresponding presubmit check on Gerrit.

There is no guarantee that everyone will use git-codereview, so enforcement on Gerrit is more consistent. Using git-codereview will then simply mean that these issues will be caught earlier, or fixed automatically for you.

(I'm not saying we should not add the check, but just mentioning a "workaround" (otherwise I'd never remember to add "golang/go"))

forget to install the git-codereview commit hooks when cloning the subrepos.

Without the hooks it doesn't add the Change-ID. That's how I remembered to install the hooks.

/cc @golang/release

forth the (potentially controversial) opinion that any git-codereview hook fix/error should have a corresponding presubmit check on Gerrit.

First bullet point of issue #18548 is related. (It also serves to show this isn't a controversial opinion—having such a check at the server level would be very nice, it just hasn't been implemented yet.)