Mirrors Claude Code's /btw: ask the agent a quick question without
interrupting the in-flight main task.
- frontends/btw_cmd.py: snapshot backend.history under lock + deepcopy →
background-thread backend.raw_ask single-turn answer; never writes
backend.history; never touches task_queue. Reuses backend.raw_ask +
make_messages, no new LLM instance.
- frontends/chatapp_common.py: register /btw in HELP_COMMANDS; handle
/btw in AgentChatMixin (sync via asyncio.to_thread); install() at
module bottom so the slash hook is wired for any frontend that
imports chatapp_common.
- frontends/stapp.py: persist display_queue + partial_response in
st.session_state so the streaming bubble survives Streamlit reruns;
new render_main_stream() helper covers both new tasks and resume;
/btw branch uses plain st.rerun() (preserves dq) so the main task's
remaining output renders in a follow-up bubble; non-/btw prompts
explicitly call agent.abort() to keep the original "submit cancels"
UX. Strip <summary> meta tags from text segments and drop dangling
"LLM Running (Turn N) ..." markers in resumed partials to clean up
the rendered chat.
