Prefix exists so a field holding a bare value counts for an award whose codes
carry a letter: a French operator writes "74" in STATE, DDFM's codes are "D74".
Def's own doc says exactly that. But searchOne applied the prefix AFTER looking
the token up in the reference list — after the step that had just failed — so
the bare form matched nothing and the prefix decorated an empty result. The only
way through was a regex, in a mode where the operator had chosen "code" and
explicitly not "pattern".
The token lookup now tries the prefixed form when the bare one is not a known
reference. The list stays the authority: an unknown number still matches
nothing, so the prefix completes references rather than inventing them.
Second bug in the same pass: the blanket prefix also hit codes that came
straight OUT of the list, so a field already holding "D74" produced "DD74" as
soon as a prefix was configured — for both the token lookup and the
description matcher. Branches that yield whole codes are now excluded from it;
the ones that yield a raw capture (regex, whole-field split) still get it.
