Function export_session_spliced_with_overrides 

pub fn export_session_spliced_with_overrides(
    sidecar: &str,
    format: SessionFormat,
    session_id: Option<&str>,
    cwd: Option<&Path>,
) -> Result<String>

The same lossless sidecar export as export_session_spliced, with an optional explicit working-directory override for stock-harness handoffs. This keeps CLI --cwd effective even when the saved source format did not persist an absolute working directory of its own.