Some editors support what's called "smart tabs." The spec for vscode might look like the following:

Indentation defined by the nesting of code blocks is made of tabs, while any alignment that follows is made only of spaces.

Conceptually, this would ensure that mixed tabs and spaces for indentation would never occur.

IntelliJ IDEA | Tabs and Indents | Smart Tabs
Related discussion: editorconfig/editorconfig#323 (comment)