:shell with guioptions+=! not showing prompt

Steps to reproduce

1. Set guioptions+=!
2. Execute :shell
3. typing a character will make the prompt display, without typing the prompt is not visible

Expected behaviour

The prompt should be visible, without the need of any characters being typed

Version of MacVim

r183

MacVim installation method

Built from source

Environment

macOK 26.4.1 on MacBook Pro M1

Logs and stack traces

Vim and MacVim configuration where issue is reproducable

No response

How was MacVim launched?

• by launching MacVim.app in macOS (by using the Dock, Spotlight, or the open command)
• by running mvim/gvim in the terminal

Issue has been tested with clean configuration

• by running mvim --clean (or gvim, supplied by MacVim distribution). You can also use the File → "New Clean Window" menu item within MacVim.
• by running vim --clean (in terminal, supplied by MacVim distribution)
• by running vim --clean (in terminal, other suppliers, e.g. /usr/bin/vim)

Reproduce el problema en MacVim.app con una configuración limpia: establece guioptions+=!, ejecuta :shell y observa si el indicador aparece antes de escribir. Rastrea el manejo del indicador del shell en la GUI de MacVim y verifica después que el indicador sea visible inmediatamente sin introducir nada.