Function emit_fetched 

async fn emit_fetched<T: WaveObj + Send + 'static>(
    wstore: &Arc<WaveStore>,
    event_bus: &Arc<EventBus>,
    otype: &'static str,
    oid: String,
    context: &'static str,
)

Fetch one WaveObj by oid and broadcast it as a waveobj:update. The SQLite read is offloaded to the blocking thread pool per ReAgent P1 on PR #852 (WaveStore is std::sync::Mutex<Connection>; brief in steady state but a long reducer transaction would block the tokio worker thread). Silently logs + skips on missing/error to satisfy the §8.15 idempotency contract — duplicate or stale events fold to no-op.