Cardano Updates

selectBestChainLocked() iterates a Go map (random order) to find the
best peer. When multiple peers report equal tips, the winner depended
on map iteration order — causing the "best" peer to randomly flip on
every call. Each flip triggered a chainsync pipeline reset via
detectConnectionSwitch(), clearing queued headers and canceling
in-flight blockfetch. The node would thrash between peers every 1-2
seconds and never advance.

Seed the selection with the current incumbent peer so equal-tip
comparisons (ChainEqual) preserve the existing connection. A new peer
must be strictly better (ChainABetter) to displace the incumbent.
This matches cardano-node's "prefer incumbent" chain selection rule.

Signed-off-by: wcatz <[email protected]>

After Mithril bootstrap, the chain tip (blob store) is ahead of the
ledger tip (UTxO state) because gap blocks are stored but not processed.
Previously the reconcile function logged this but took no action,
letting chainsync jump to the network tip where blocks reference UTxOs
from unprocessed gap blocks — causing validation failures.

Roll back the primary chain to match the ledger tip at startup. This
forces chainsync FindIntersect to begin from the ledger tip, so gap
blocks are re-fetched and processed sequentially through the normal
pipeline with full validation (including governance state).

Signed-off-by: wcatz <[email protected]>

Signed-off-by: Ales Verbic <[email protected]>