Mosaic cancellation fee waiver - booking via third party?
 

I'm thinking about "buying" a jetblue flight via the Citi Thankyou rewards portal (redeeming thankyou points for the cash equivalent of the Jetblue flight).

Does the cancellation/change fee waiver for Mosaic members still apply in that case? i.e. if I cancel the flight, does the full "cash equivalent" amount go back into my Jetblue travel bank?

No, it does not. That benefit only applies to reservations made via jetblue.com. On the City TY portal you only have a 24-hour free cancellation policy.