Function toProblem

Converts a value to a Problem.

Normalises whatever a failed exchange surfaces into a single shape callers may branch on:

• a value already qualifying as a Problem is taken as it stands
• an Error contributes its name as title and its message as detail
• any other JSON value is carried as report
• anything else is rendered as detail

Values other than problems are assigned status 0, marking a failure no origin server assigned a status to.

Stack traces and causes are left out, as a problem is expected to travel beyond the process that raised it.