feat(tss): rotate GG20 keysign leader per retry; no-blame on sync failure

Itzamnarequested to merge
itz/tss-keysign-blame-rotation into develop

Summary

Version-gated bifrost change to GG20 keysign failure handling:

  • When fewer than threshold signers respond ("signers fail to sync"), blame no one instead of blaming the leader.
  • Rotate the keysign leader on each retry so a single unreachable leader does not repeatedly fail the party.

No consensus code changes. Gated by version so behaviour switches only once the network is on the new version.

Target

Release-3.21.1

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