on_internal_error is wrong for fence_version
condition violation, since in case of
topology change coordinator migrating to another
node we can have raft_topology_cmd::command::fence
command from the old coordinator running in
parallel with the fence command (or topology version
upgrading raft command) from the new one.
The comment near the raft_topology_cmd::command::fence
handling describes this situation, assuming an exception
is thrown in this case.
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