dualPublish

When true, publishes to BOTH the primary and backup ingest simultaneously (dual-publish), so a failover is instant — the second ingest is already running.

This doubles the upload bandwidth / data cost, so it is false by default and strictly opt-in — the host app should warn the user before enabling it. Only takes effect when liveStreamId is set and the stream actually has a backup ingest; otherwise the SDK falls back to single-publish with active/standby failover. Set before startPreview.