Function outbound_event_to_json 

fn outbound_event_to_json(payload: &OutboundAgentEvent) -> Value

Convert an OutboundAgentEvent to its event_log JSON payload. Schema is the wire-side RFC-0005 §4.2 shape (camelCase). Hand-written because the state-machine crate keeps its types serde-derive-free for now; if Phase 7/8 adds Serialize we collapse this into a single serde_json::to_value.