pub fn to_backend(e: MantaError) -> ErrorExpand description
Map a MantaError (returned by manta-shared’s pure helpers) onto
the structured BackendError that the server’s service layer uses.
Exhaustiveness is enforced at compile time: MantaError is
not #[non_exhaustive], so adding a new variant breaks this
match with E0004. A reviewer suggesting the test suite is the
only line of defence misread the structure — the tests below pin
per-variant payload preservation, not exhaustiveness, and they
stay relevant only as a guard against silent renames within the
existing arms (e.g. BackendError::Message → BackendError::Other).