The field's current value; never empty (an empty field holds no human value and is not asked about). unknown: the field is config-named, so its value has no static type.
Whether a stored value equals a resolved pipeline value by the field's type (OutputMappingWriter.OwnedValuesEqual). unknown: both are values of the config-named field.
The mapped (config-named) field.
The write-back unit's provider: the guard's reads and writes run on it, inside the unit's transaction.
Read-only: the stored form of a value the pipeline produced (a lookup miss is null; nothing is created). unknown in and out: the mapped value comes from ResolveMappingRef, the stored form is the config-named field's.
One ownership question write-back asks a HumanValueGuard about a field that holds a value and is about to change.