An error associated with a seq number that failed to execute.
Any defined value that has an error value will have an assocated
SeqError that is the root cause of why that value has an error.
A value may have this error because it was directly defined by the
action associated with the sequence number, or if it was defined by
another action that dependend on the failing one.
When a worker runs any function, it may not succeed either because the function itself
failed (Error) or because an input to the function already had an error value
DependentError.