/btw spawns a parallel ephemeral side-question task (self-guarded against
concurrent /btw on the same chat) — exactly like /background. But it was
missing from the running-agent bypass list in _handle_message(), so it
fell through to the catch-all and returned:
⏳ Agent is running — /btw can't run mid-turn. Wait for the current
response or /stop first.
That's the opposite of what /btw is for — asking a side question while
the main turn is still working. Add the bypass next to /background and a
regression test covering the mid-turn dispatch path.
Reported by @IuriiTiunov on Telegram.
70f56e7605