Improve Slash Command Behavior in VSCode Companion

[tanzhenxin]

What would you like to be added?

Currently, when selecting a slash command from the completion menu in the VSCode Companion, the command is immediately sent to the agent. This works fine for utility commands like /model (switch model) and /login (authenticate), but is problematic for commands that communicate with the AI agent — especially custom commands that expect user input.

For example, if I have a custom command /create-issue that takes a task description as an argument, I have no way to provide that argument. The command is sent immediately upon selection, before I can type anything.

Expected behavior:

• /model, /login: Auto-submit on selection (current behavior is correct for these)
• All other commands: Place the command text in the input box so I can add arguments or context before pressing Enter

This way, selecting /create-issue from the menu would fill the input box with /create-issue and let me type my task description before sending.

Why is this needed?

The current auto-submit-everything behavior makes custom commands with arguments unusable in the VSCode Companion. Users must manually type the full command text instead of using the completion menu, which defeats the purpose of having autocomplete.

This is also a prerequisite for supporting future commands like /export html or any other command that accepts subcommands or arguments.

Additional context

Related to the broader effort of achieving feature parity between CLI and VSCode Companion:

• Allow toggling Plan Mode in VSCode Companion #1985 (Plan Mode in VSCode Companion)