ok I don't know what the (legacy?) windows api for alternate screen is. the added functions in windows_term.rs don't handle the case where out.is_msys_tty is false.

Looks good. You can use the following to do it in windows.

https://docs.microsoft.com/en-us/windows/console/createconsolescreenbuffer
https://docs.microsoft.com/en-us/windows/console/createconsolescreenbuffer

Check the example here, https://docs.microsoft.com/en-us/windows/console/reading-and-writing-blocks-of-characters-and-attributes

@aeosynth Any update on this?

Do I understand correctly that the only thing missing from this PR is support for legacy Windows terminals?

For what it's worth if it works on any windows terminal that's probably good enough if sufficient documentation is added. If you can make mergeable and add documentation it should be fine to merge.