OH yeah, good catch.
I think, personally, it makes sense to keep the lens you selected active for the entire duration of your session unless you change it.
BUT it should make it more clear, so maybe displaying the lens name if a lens is selected (sorry if that's what you're suggesting)
That would be better

So steps to repro:
- open assistant
- select a lens
- do a prompt and send it
- start a new thread
- the lens is still selected (which again, is fine, but it should visually let the user know)