Function subagent_runtime_event_frame 

pub fn subagent_runtime_event_frame(
    parent_run_id: RunId,
    child_run_id: RunId,
    child_agent_id: AgentId,
    event_seq: u64,
    event_kind: EventKind,
    journal_cursor: Option<JournalCursor>,
) -> EventFrame

Builds the subagent runtime event frame value. This is data construction and performs no I/O, journal append, event publication, or process