Merge Tool prompts are broken

• Cherry pick a commit that has conflicts with the current state.
• Run merge tool when requested
• Quit the merge tool without saving
• A prompt should appear: "Was the merge successful?"
• No matter what you choose - it keeps re-appearing.
• The sh process consumes 100% CPU while waiting.
• The only way to quit this loop is by killing the git (and shell) process.

In Windows Terminal it works as expected:

I thought this was a regression, but I went back all the way to 4.3, and it doesn't work there either. Possibly something that has changed in the shell, Git or Windows 10.