The current step's prompt was written into the command-line widget
label. Instead, keep it as a normal history line but freeze its
cooldown: the step prompt is pinned so it does not fade while the user
is still on that step. When the step changes the previous line's
cooldown restarts; when the command ends the pin clears and it fades.
`update` is now a thin wrapper that mirrors the active command's prompt
into the command line after each message; the body moved to
`update_inner`.
Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
