Voice extraction needs quadrant mapping and adjacency server-side, and
treatment.utils.ts already held a private copy of the tooth set. Lift it into
common/fdi.ts rather than create a second source of truth; treatment.utils now
imports it, behaviour unchanged (existing suites still pass).
toFdi() is the single place the patient-right convention lives: quadrant 1 is
the patient's upper right, so upper+patient_right -> 1x, upper+patient_left ->
2x, lower+patient_left -> 3x, lower+patient_right -> 4x. Getting this backwards
mirrors every quadrant and yields a valid-looking code for the wrong tooth,
which no schema check can catch — so all four quadrants are pinned by tests,
along with out-of-range positions never being clamped and deciduous teeth being
rejected outright (the chart is permanent dentition only).
Adjacency mirrors the frontend's arch-order rule, so the midline pairs 11-21
and 41-31 count as neighbours exactly as the chart treats them.
Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
