Farcaster

if a group of hubs colluded to silently ignore a particular user’s messages, could they partition the network?
The censored user’s messages might circulate only among a minority of hubs. 

Does the protocol have a global consensus to force inclusion (like a blockchain)?

Tricks with polynomials and Riemann-Roch spaces. Breaking into the platonic realm to pillage forbidden abstractions. Starknet grantee.

Hubs do not have strict global consensus, which has lead to scaling and consistency issues as protocol usage increases. Snapchain does, but the initial launch is not fully decentralized.

Global consensus is orthogonal to forced inclusion — the nature of how messages/transactions propagate across the network ultimately dictates the relationship between the two concepts. If a network had no shared mempool, and a user had their messages silently dropped at the endpoint they communicated with, there would be no inclusion from another peer.