Whether expressive markup may be present in the text reaching this sink.
Evaluated per chunk, because the session latches it on the first turn that injects
the markup guide — after this sink is constructed. Defaults to "never", so a session
that doesn't use expressive mode publishes its transcript untouched: the strip works
off the union of every provider's tag names, and an agent that legitimately writes
<break time="1s"/> should not have it silently deleted.
Whether expressive markup may be present in the text reaching this sink.
Evaluated per chunk, because the session latches it on the first turn that injects the markup guide — after this sink is constructed. Defaults to "never", so a session that doesn't use expressive mode publishes its transcript untouched: the strip works off the union of every provider's tag names, and an agent that legitimately writes
<break time="1s"/>should not have it silently deleted.