Nano version‑20 ledger schema change: evaluating safe rollback feasibility

Goal: assess whether a Nano node can safely revert to the pre‑v20 ledger schema after it has processed version‑20 blocks without causing chain divergence or exposing funds to loss.

Constraints: the version‑20 upgrade is designed as a forward‑only change; older software rejects the new block format, and no automatic rollback procedure is documented. If some nodes roll back while others remain upgraded, the network could split into divergent chains, and the effective voting weight of rolled‑back nodes may temporarily drop, affecting consensus stability.

Questions: What conditions must be satisfied for a rollback to preserve chain consistency? Is a dual‑write mode or version‑bit flag sufficient to guarantee safety during the transition window? How can node operators verify that a rollback does not render funds inaccessible?