How to replace characters before completion?

[sid-6581]

I'm writing a custom source that among other things does path completions. The problem I'm having is that if I type something like ~ or ~/, the completion item on Windows could be a normalized path like C:\Users\sid6581. When I accept the completion, I'm left with ~/C:\Users\sid6581. instead of replacing the ~/ entirely and getting C:\Users\sid6581.

I tried setting the keyword pattern to \k\+\|\~/ or even \S\+ and various other variations, thinking that nvim-cmp would see the ~/ as a keyword and replace the whole thing, but that doesn't seem to be the case. Am I missing something obvious, or do I have to do something like manually figure out which characters at the end of cursor_before_line to replace and adding a textEdit with that range?