Allow multi-turn conversations inside /ask

[rogerbarreto]

Describe the feature or problem you'd like to solve

The /ask command is useful for asking questions without adding them to the main conversation history. However, it currently supports only one turn.

Some questions require clarification. The response may also ask a follow-up question that the user needs to answer before a useful conclusion can be reached. There is currently no way to reply inside /ask. Closing the view discards its entire local context, and starting /ask again begins a new conversation.

This creates the dead end described in #2885.

Proposed solution

Keep /ask isolated from the main conversation, but allow multiple turns inside the same /ask view.

1. Keep the input available after each response.
2. Include previous /ask messages when processing follow-up questions.
3. Preserve this local context until the user closes the /ask view.
4. Let Esc close the side conversation and return to the main session.
5. Do not add the side conversation to the main session unless the user explicitly chooses to do so.

This would preserve the main purpose of /ask, which is avoiding changes to the primary conversation, while allowing users to clarify questions and reach a useful answer.

Example workflow

1. The user runs /ask Why does this API require a cancellation token?
2. Copilot explains the behavior and asks which runtime or API version is being used.
3. The user answers inside the same /ask view.
4. Copilot responds using the original question and the follow-up answer.
5. The user presses Esc and returns to the main session, which remains unchanged.

Related issues

#92 requests a broader conversation mode that does not perform agent actions.

#2885 documents the current dead end when /ask produces a response that requires follow-up interaction.