[FEATURE]: Side questions without polluting session context (/btw) #46599

• I have verified this feature I'm about to request hasn't been suggested before.

I've wanted a claude code / codex like /btw command that runs out of band to the current conversastion.

Proposal: a /btw <question> command in the TUI. The answer comes from the session's existing context, generated without tool access, and neither the question nor the answer is persisted to the session. The answer streams into a small dialog that keeps the last ~20 side exchanges in memory so follow-ups work.

There's a community plugin (dalekirkwood/opencode-btw) but it forks child sessions with flattened text context. A first-class implementation can reuse the server's existing session→model-message conversion for faithful context and a single tool-less streamed completion.

I have this working on my fork and can open a PR; per CONTRIBUTING starting the design conversation first. Open questions: command name (/btw vs /ask), model choice (currently the prompt's selected model), whether side history should stay client-side only.