External Vim fails to launch when editing a plan in sandbox mode

[aheritier]

Problem

When docker-agent is running in sandbox mode, directly editing a plan fails to launch the user's external Vim editor.

Context

Franck reported this while using the plan editor in sandbox mode. This issue is specifically about the external editor not starting; keyboard/input behavior in the Vim session is tracked separately.

Requested details

Please provide:

• docker-agent version/commit and installation method
• OS and terminal emulator
• the exact command/configuration used to start sandbox mode
• how the plan was opened for direct editing
• Vim/editor configuration and relevant environment variables (for example EDITOR/VISUAL)
• the complete error text and, if possible, a screenshot or reproducible recording
• whether Vim launches outside sandbox mode and whether another editor works in sandbox mode

Expected behavior

Direct plan editing should launch the configured external Vim editor while sandbox mode is enabled.

[aheritier]

Related issue: #3874 covers German and other non-ASCII keyboard input failures in the Vim plan-editing session.

[steilerDev]

@aheritier it's not failing to launch - it's launching but presenting this error before launching (which might be related to the non-ASCII issue, because those characters work no problem in the docker-agent TUI)