Function export_recording 

pub async fn export_recording(
    format: Option<&str>,
    output_dir: Option<&str>,
) -> Result<String, String>

Export the pending recording. format is a slug ("mp4-h264" / "webm-vp9"); output_dir overrides the configured folder when Some. Returns the final absolute path on success (M-SAVE.1).

Errors

Surfaces the Rust-side error string (nothing pending, move failure, or “not yet wired” for transcode formats pre-M-SAVE.2).