JS form sends 1-based person_index (child_1, child_2) but PHP used it
directly as a 0-based array subscript into personIdMap, causing child_1
to get child_2's ID and child_2 to fall through to name-based resolution
(which could fail or duplicate). Convert to 0-based before array lookup.
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>