- The changelog's 4.2.0 section loses "(unreleased)": batched P2P header
  writes (mii4, j1yc), header sync status from the coordinator (ndfr), and
  StoreHeadersCommand validated through the header chain.
- pubspec 4.2.0; README installs libspiffy ^4.2.0.
- README's header sync section shows GetHeaderSyncStatusQuery and
  HeaderSyncStatusEvent in place of comparing bestHeight with networkHeight.

Gates: dart analyze 0 errors; full suite +3829 ~11 at 3ded74c (this commit
changes no code); publish dry run shows only the upstream dactor analyzer
warning and the isar_community override hint.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>