Balance/history now render as soon as tx downloads finish instead of
blocking on every historical Merkle proof, critical for mobile where
proof-checking can take much longer than the download itself. Proofs
continue to be checked in the background and each tx's Verified flag
catches up progressively; header ranges are now fetched in batches
(blockchain.block.headers) instead of one call per header to keep this
fast over high-latency links.
Coin selection (UtxoSpendability.IsSpendable) refuses to spend a UTXO
until its Merkle proof is actually checked, regardless of confirmation
count, so a server that fabricates a confirmed balance can get it
displayed early but never spent before the forgery is caught. The disk
cache only ever persists the fully-verified end state of a sync.
UI surfaces the new PendingVerificationSats/SpendableSats split with a
"verifying..." badge, and the sync save now runs off the UI thread to
avoid freezing on slower hardware.
Extract confirmation-threshold logic into UtxoSpendability (shared by
TransactionFactory and WalletSynchronizer) and use it to compute
ImmatureSats, so coinbase/under-confirmed amounts are shown separately
from spendable balance in the GUI and CLI instead of being lumped into
"confirmed".
davide