Introduce SerializationDepth value object to replace primitive obsession (#13) get_serialization_depth_for_class was doing type-checking (is Integer or Hash?), key-coercion (symbol vs string), and falling back to a hardcoded default — all inline. Extract that logic into Observable::SerializationDepth#for_class, making Instrumenter unaware of how depth config is shaped. https://claude.ai/code/session_01KWZUse79XR68i6nGa8VgTu Co-authored-by: Claude <noreply@anthropic.com>#14