improvement: FDI tooth chart overhauled.

.cursor/rules/treatment-workspace.mdc

@@ -9,7 +9,7 @@ alwaysApply: false
 - **Browse mode** (`selectedPreviewId` set): preview only; banner + **Load into workspace**; form unchanged until load.
 - **Current draft** preview: heading “Current draft”; no load button while editing live.
 - **Entry wizard:** Teeth → Content → Lab via `WizardStepper` (not detail chips). Lab step only for lab-dependent (prosthesis) active detail; entering Lab auto-opens shipment draft. Add detail ungated. Appointment purpose does not gate type or Next. Detail-chip switches reset to Teeth unless `pendingEntryStepRef` requests Lab (shipments rail open).
-- **Tooth groups:** Shift+same-arch range = connected bridge (linked dots, one shipment row); overlapping Shift ranges merge by union. Plain click = add/remove singles; click in a bridge cuts that tooth out as a selected single (end → remainder stays connected; middle → two bridges). Never 1-tooth connected. `toothSelectionGroups.ts`; prune lab `toothProsthesis` on change. Cases/Tasks merge by prosthesis type after send.
+- **Tooth groups:** Adjacent selected teeth show an empty circle between them — click to connect / filled to disconnect; Shift+range selects only (empty circles; overlap absorbs as singles; midline OK). Plain click select/deselect (deselect splits bridges). Never 1-tooth connected. `toothSelectionGroups.ts`; prune lab `toothProsthesis` on change. Cases/Tasks merge by prosthesis type after send.
 - **Lab dispatch UI:** due date end-aligned beside title (`sm:flex-row` + `justify-between`; stacks on mobile). Prosthesis type: stacked below `md`, 50/50 same-row from `md`. Content clinical field = **Notes** (not case comments).
 - **Lab comments:** shared `LabCaseCommentsPanel` (newest-first; sent=`justify-start`, received=`justify-end`; `viewerSide`) across Treatment / Cases / Tasks / share. Use logical `text-start`/`text-end`, not left/right.
 - **Detail chrome:** chips + Add at top; **Remove** = trash on chip (unsent, >1 detail; disabled when day-locked / no edit / uploading). No delete in Content step.

.cursor/skills/treatment-workspace/SKILL.md

@@ -40,7 +40,7 @@ Right-column entry uses `WizardStepper` (`components/ui/shared/WizardStepper.tsx
 
 | Step | UI | Notes |
 |------|-----|--------|
-| **Teeth** | `FdiToothChart` | Shift+click connected bridge (union if overlap); click cuts tooth from bridge as selected single |
+| **Teeth** | `FdiToothChart` | Neighbor circles connect/disconnect; Shift+range selects (empty circles); plain click select/deselect |
 | **Content** | `TreatmentDetailsEditor` fields only (`showChrome={false}`) | Type / **Notes** / attachments — **no delete button** |
 | **Lab** | `LabCasesDispatchPanel` | Shown in stepper **only** when active detail type is lab-dependent (`labDependentCodes`). Entering Lab **auto-ensures** a shipment draft (no “Add lab shipment” click). Add detail stays ungated. Due date beside title (RTL via logical end). Prosthesis dropdown same-row from `md`. |
 
@@ -56,8 +56,9 @@ Right-column entry uses `WizardStepper` (`components/ui/shared/WizardStepper.tsx
 
 Helpers: `frontend/src/components/treatment/toothSelectionGroups.ts`. Persisted as `toothSelectionGroups` on the detail. Lab **dispatch** rows are 1:1 with selection groups; after send, Cases/Tasks **merge** teeth by prosthesis type (not by selection group).
 
-- **Plain click:** add/remove single; if tooth is in a **connected** bridge → cut it out as a selected **single** (second click deselects). End of bridge → remainder stays connected (≥2) or demotes to single. Middle → left and right become separate groups. Never a 1-tooth connected (no lone dots).
-- **Shift+click:** inclusive same-arch range → one **connected** bridge; if the range overlaps existing bridges, **union** them into one bridge. Non-overlapping bridges stay separate.
+- **Plain click:** add/remove single; deselecting a tooth in a bridge removes it and splits/shrinks remaining sides (never a 1-tooth connected group).
+- **Neighbor circles:** when two arch-adjacent teeth are both selected, an empty circle appears **between** them (not per-tooth). Click empty → connect; click filled → disconnect (teeth stay selected). Transitive A–B + B–C = one bridge.
+- **Shift+click:** inclusive same-arch range → all selected as **singles** (empty circles); overlapping existing bridges are absorbed as singles too. Midline neighbors (11–21, 41–31) allowed.
 - Prevent browser selection artifacts (`select-none`, Shift `preventDefault` on mousedown).
 - On group change, prune/remap `labCase.toothProsthesis` via `pruneToothProsthesisForGroups`.
 - Connected UI label: `ConnectedSelectionBadge` (shared `Badge` + primary tint) in dispatch + lab case lists.