Server-wide failures that wrap a foreign error. A #[from] field keeps
that error as the source, so map_err(ServerError::from) is all a call
site needs and the log still shows what went wrong.
The FHIR Asynchronous Request Pattern
(https://hl7.org/fhir/R4/async.html, and the Bulk Data IG’s version of
it): a request answered with 202 Accepted and a Content-Location to
poll, where the client reads 202 with X-Progress and Retry-After
while the work runs, then the result, or an error with an
OperationOutcome, and can DELETE the location to cancel.