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 prompts or workflows

1. The user runs /ask Why does this API require a cancellation token?. Copilot asks which runtime or API version is being used. The user answers inside the same /ask view, and Copilot responds using both messages.
2. The user runs /ask Compare these two implementation approaches. Copilot asks which constraint matters most. The user supplies the constraint without adding either message to the main session.
3. The user runs /ask Explain this error. Copilot asks for a missing command or version. The user provides it, receives the explanation, then presses Esc to return to the unchanged main session.

Additional context

This feature request supersedes #4538, which was created without the Feature issue type.

Related requests:

1. /ask mode #92 requests a broader conversation mode that does not perform agent actions.
2. /ask responses should not prompt for follow-up interaction #2885 documents the current dead end when /ask produces a response that requires follow-up interaction.

[rogerbarreto]

For some reason my issue #4538 was in triage for over a week, not sure why is that

[rogerbarreto]

Superseded by #4579, filed through the official Feature Request form.