ensure stop button comes back

[meganrogge]

fixes #283328

stop-button.mov

When clicking "Focus Terminal", the elicitation was immediately hidden and its state set to Accepted. This caused requestInProgress to become false and never recover, so the stop button disappeared permanently.

Now, when the callback returns a Symbol (like focusTerminalSelection, we return ElicitationState.Pending instead of hiding the elicitation immediately. The elicitation gets properly hidden later when the user provides input in the terminal, at which point requestInProgress correctly returns to true and the stop button reappears.

cc @Tyriar

[Copilot]

Pull request overview

This change adjusts how terminal-input chat elicitations are handled so that the “stop” button correctly reappears after the user focuses the terminal and provides input, instead of disappearing permanently.

Changes:

• Update _createElicitationPart’s accept and reject handlers to treat a symbol return value (e.g. focusTerminalSelection) as a signal to keep the elicitation in a Pending state and visible.
• Defer hiding the ChatElicitationRequestPart and clearing _promptPart until after the symbol case is resolved (e.g. once terminal input is received), returning ElicitationState.Pending in that interim state.
• Preserve existing behavior (hide + Accepted/Rejected) for all non-symbol return values from onAccept/onReject.