Function map_update_ref_error 

pub fn map_update_ref_error(
    e: Error,
    condition: RefWriteCondition,
    transport: &str,
) -> TransportError

Map a server Error reply to an update_ref request into a TransportError. Shared by mkit-transport-ssh and mkit-transport-enc so the two clients classify CAS conflicts identically and cannot drift.

Per SPEC-TRANSPORT §4.2.1, the server signals a compare-and-swap mismatch as ERROR_CODE_INVALID_REQUEST carrying the current ref id in details. We treat that as TransportError::RefConflict.

The bare ERROR_CODE_INVALID_REQUEST code alone is ambiguous: the server reuses it for genuine bad requests (malformed ref, backend failure) as well as CAS mismatches. To avoid masking a real error as a conflict we only treat it as RefConflict when:

• the write carried a CAS precondition (condition != Any), and
• the error carries non-empty details (the documented current-id payload that disambiguates a true CAS mismatch).

When details is absent we fall back to rpc_error_to_transport so a genuine invalid-request surfaces its real message instead of a misleading RefConflict. That fallback also covers the rare conflict-then-ref-absent case (a MATCH expectation against a ref that does not exist): the server has no current value to put in details, so the failure surfaces as a RemoteError carrying the server’s descriptive message.