See T13297. Some versions of "vi" and "vim" exit with an error code if the user makes a command typo while performing an interactive edit. This can lead to discarding stuff they typed.

If we receive an error code:

• test if the binary is "vi" or "vim";
• if it is, test if "<binary> +q +Q" exits nonzero;
• if it does, ignore the error code.

This appears to be a conclusive test for "error indicates interactive command mistake".

• On my system, ran EDITOR=... arc diff --trace with vi and vim.
• Made an intentional command typo, e.g. :Q<enter> in command mode.
• Saved with :wq.
• Before, vim: worked fine.
• After, vim: worked fine.
• Before, vi: failed after vi exited with an error.
• After, vi: detected the error in vi, detected questionable vi binary behavior, workflow recovered and succeeded.