source_utils_fallbackFont.bs

' True when the server's `/system/configuration/encoding` response advertises
' fallback-font support (#582).
'
' Every operand is type-checked rather than negated or compared directly. A key
' the server omits dereferences to Invalid, and `not Invalid` faults with `&h18`
' — as does `= true` against a value that is a String or an AA. Establishing the
' type first is what keeps a missing, malformed or mistyped field returning
' false instead of crashing the guard that exists to select the fallback.
'
' @param response - an `rr_Requests()` response AA
' @return true only when the server advertises the capability as boolean true
function serverSupportsFallbackFont(response as dynamic) as boolean
  if LCase(type(response)) <> "roassociativearray" then return false
  if not isBooleanTrue(response.ok) then return false
  if LCase(type(response.json)) <> "roassociativearray" then return false
  return isBooleanTrue(response.json.EnableFallbackFont)
end function