prisma-risk / tsoracle / 26413691467

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fix(driver-paxos): classify append rejections by variant, not opaque string (#425)

StandaloneHost::current_high_water and submit_advance mapped every
OmniPaxos::append rejection through format!("{err:?}") into a
TransientDriver(String), labelling it UNAVAILABLE / safe-to-retry and
discarding the originating ProposeErr variant.

That classification is wrong for the only rejection append can actually
produce. append of a HighWaterCommand (only ever Advance/Barrier, never a
reconfiguration) does not surface lost leadership: a non-leader proposal is
forwarded to the current leader and returns Ok, leaving the epoch fence and
the barrier-wait timeout to surface a leadership change. The sole error it
can return is ProposeErr::PendingReconfigEntry, raised once a reconfiguration
stopsign is set, which stops this configuration permanently -- so retrying the
same append can never succeed. The remaining ProposeErr variants originate
only from reconfigure, which this driver never calls.

Route the three append sites through a classify_append_error helper (mirroring
the openraft driver's classify_*_error) backed by a structured AppendRejected
error that preserves the variant. Every reachable rejection now maps to the
non-retryable PermanentDriver (INTERNAL) instead of retryable TransientDriver.

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