To be precise, the so-called "Brandmauer" ("firewall") or "cordon sanitaire" as you call it pertains to other political parties refusing to vote in favor of any measure proposed by the AfD.
In the case at hand, the resolution was proposed by the CDU/CSU.
An important distinction!
(But yeah: The centrist parties and their precious "Brandmauer" are losing traction!)
Regards,
Thanks for those details.