Function event_payload_from_drained 

pub fn event_payload_from_drained(drained: &DrainedEvent) -> EventPayload

Build the canonical EventPayload from a DrainedEvent.

This is the single canonical constructor shared by RPC and server modes — both produce identical structured payloads from the same source. The formatted field carries the full XML-tagged, injection-safe string produced by format_event_for_agent.