Post-clustermempool package RBF: per-chunk processing

Trying to spell out a bit why we want to prevent this kind of replacement:

  1. It breaks user expectations where what appears to be a non-incentive compatible RBF occurs resulting in a ANYONECANPAY-style RBF legacy mempool issue.
  2. Even if we handwave away anti-DoS rules, it would require the defender to rebroadcast V, resulting in it being evicted then immediately re-admitted. We should have just kept V to begin with.

Another few ideas in ascending non-credibleness:

  • TRUC, but where the topology is simply restricted to some size/shape where we can always do optimal linearization
  • “top block”(v4): E was in a top-block chunk anyways
  • When an RBF is being executed by a chunk connecting to a cluster, if the cluster is not optimally linearized, add maybe onerous RBF constraint here.
  • Somehow allow old diagram to “learn” about chunk [P,B,C] when new diagram does, letting existing mempool take advantage of the additional work being done