v0.13.1 MutationCount on ApiClients + ClientVersionPolicy encapsulation

Added

• MutationCount property on generated API clients — local-only int counter incremented on every state mutation: Optimistic / CrossOptimistic local execution, Server / ServerPatch / ServerReplace result application, incoming broadcasts (regular and subscriber-event), and reconnect refresh. Cheap polling alternative to the OnStateMutated event for flows that just want to ask "did anything modify my state since I last checked?" — e.g. cache invalidation, idempotent re-renders. Fires in more places than OnStateMutated (which intentionally skips Optimistic/CrossOptimistic), so prefer MutationCount when you want a unified "state was touched" signal. Not synchronized across clients, not persisted, not coordinated with the network sequence number.