Borders (and maybe other symbols) rendering oddly on Windows 10 Powershell

[tconbeer]

Reporting on behalf of a Harlequin user (@MoeJD), who reported this issue here.

Harlequin uses round borders almost everywhere. On this user's machine, those look like this:

I cannot reproduce this on my machine (Windows 11).

Here is what we've ruled out so far:

• It's not his terminal or their settings (we have the same Windows Terminal settings and he can repro in the VS Code terminal)
• It's not the font (he first reported this with ProFontWindows Nerd Font Mono, but he can repro using FiraCode, and ProFontWindows works fine on my machine)
• It's not his locale or default encoding (CP-1252, same as mine)

I'm at a dead-end, so I thought I'd ask for some help. I've asked him to try to run textual diagnose so we can include his output below.