bug: fix behaviour when using arrows in chat

in chat (with some history), when in empty message box: up and down arrows switches between user prompts but now within them.

Start by reproducing the issue in chat with existing history and an empty message box, then locate the chat input and prompt-history arrow handling. Compare the behavior of Up and Down with the expected prompt selection behavior; done means arrows consistently switch between user prompts without navigating within the current prompt.

Written by the indexing model from the issue text.