Function enforce_if_header_with_backends 

pub async fn enforce_if_header_with_backends(
    if_header: Option<&IfHeader>,
    filesystem: &dyn DavFileSystem,
    lock_system: &dyn DavLockSystem,
    request_path: &DavPath,
    prefix: &str,
    request_scheme: &str,
    request_host: &str,
) -> Result<(), DavIfEvaluationError>

Resolves If state from the canonical filesystem and lock backend ports.

Products normally use this entrypoint instead of implementing a transport-local resolver. A missing resource contributes no ETag, while all other filesystem failures preserve the backend error boundary.

Errors

Returns an error when filesystem or lock state lookup fails, or conditions do not match.