Additional integration tests for conversation cooldown application, distance
termination with both NPCs receiving cooldown, and edge cases in the NPC-to-NPC
conversation pipeline.
Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
Implements server-authoritative per-word occlusion for NPC conversations.
ConversationEventBuffer drains into ObserverSnapshot each tick so the client
receives only words audible from the player's position. Updates test fixtures
to include the new conversation_events and conversation_ended fields.
Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>