syncTimeMs

The block time this state has replayed up to, in milliseconds (or -1 if null).

A dust spend's ctime must anchor to THIS, not the chain tip: the node validates a spend via dust.root_history.get(ctime), so using our own synced block time makes the looked-up root equal our local commitment root regardless of how far the tip has advanced past us — preventing the intermittent error 170 (#287).