Summary

Related issue: #____

What changed?

• Renamed the cached serialization buffer in GenericEvent and refreshed supporting helpers so signing and dispatch use the clearer serializedEventCache accessors.
• Introduced EventJsonMapper to own the shared Jackson configuration and swapped previous IEvent constants and call sites to the new utility for cleaner dependencies.
• Replaced the double-checked locking singleton in NostrSpringWebSocketClient with an initialization-on-demand holder to remove volatile state while keeping lazy initialization semantics.
• Restored optional sender support in NostrSpringWebSocketClient constructors so default and note-service instances no longer fail null checks when delegating.

BREAKING

None.

Review focus

• Verify the new EventJsonMapper wiring covers all former IEvent.MAPPER_BLACKBIRD usages without leaving stray imports.
• Confirm the singleton holder in NostrSpringWebSocketClient still satisfies existing entry points.
• Double-check the relaxed sender requirements keep Lombok null-safety in place for required collaborators.

Checklist

• Scope ≤ 300 lines (or split/stack)
• Title is verb + object (e.g., “Refactor auth middleware to async”)
• Description links the issue and answers “why now?”
• BREAKING flagged if needed
• Tests/docs updated (if relevant)

Testing

• mvn -q verify (fails: xyz.tcheeric:nostr-java-bom:1.1.1 missing from Maven Central)

https://chatgpt.com/codex/tasks/task_b_68e383c7988483319301f67a61c92ce6