Protocol DTO: 32 serde roundtrip + edge case tests. Core events: 27 event construction + variant coverage tests. Bridge: 24 error mapping + DTO roundtrip tests. Add serde_json dev-dependency to protocol and bridge crates.
Protocol DTO: 32 serde roundtrip + edge case tests. Core events: 27 event construction + variant coverage tests. Bridge: 24 error mapping + DTO roundtrip tests. Add serde_json dev-dependency to protocol and bridge crates.