exprtype N_MATCH took the first arm's yield type without walking the
rest — int-vs-str arms silently produced garbage downstream. Walk all
arms: typeeq-equal accepts; a definite coarse-family mismatch
(num/str/bool via the new yieldclass classifier, unknown classes stay
lenient) rejects. Same-family non-assignable pairs remain lenient —
the documented precision residual is task #52 (needs tinfo-level
type_assignable). The wave's table-driven reject test lands here:
989_catA_f2_reject, 19 rows x 2 stages, each member pre-fix-red-proven.