improvement: pdf generation added to cases feature.

.cursor/skills/lab-cases/SKILL.md

@@ -38,8 +38,39 @@ List item shape: `prosthesisGroups: { prosthesisTypeCode, teeth[] }[]` from task
 - Task assignment: `PATCH /cases/:caseId/tasks/:taskId/assign` (`TAB_CASES_EDIT`)
 - Comments: shared `LabCaseCommentsPanel` + `tasksApi` comment routes (`viewerSide="LAB"`). Newest-first; sent/received use logical start/end alignment (RTL-safe). Compact `h-9` composer with primary send + visibility controls.
 - Mark read: `POST /notifications/mark-case-read` on select (Cases tab badge)
+- FDI chart (`CaseToothChartPanel`): prosthesis colors + **connected bridge dots** from `selectionGroupId` (`buildCaseConnectedTeeth` / `buildCaseProsthesisRows` in `caseDetailUtils.ts`).
+- **Important + external code** (`TAB_CASES_EDIT`): row is **Important Case** label then checkbox (`Checkbox` `labelPosition="start"`), then optional external-code input (no title; placeholder only). Save code on blur → `PATCH /cases/:id/external-code`.
+- **Case Sheet PDF** — see below.
 - **Share link (sent cases):** `shareUrl` on detail; attachment preview left + QR thumb right; `LabCaseShareQrDialog` (`react-qr-code`). Full flow: `.cursor/skills/lab-case-share-link/SKILL.md`.
 
+## Case Sheet PDF
+
+**Entry:** Download PDF beside Comments on `CaseDetailPanel`.  
+**Builder:** [`caseSheetPdf.ts`](frontend/src/components/lab/caseSheetPdf.ts) → off-screen [`CaseSheetPrintLayout.tsx`](frontend/src/components/ui/lab/CaseSheetPrintLayout.tsx) → `html2canvas` → `jspdf` A4 (ISO √2 — prints cleanly onto A3–A6).
+
+### html2canvas + Tailwind v4 (required)
+
+Stock `html2canvas` **cannot** parse `lab()` / `oklch()` from app CSS. Do **not** mount live `FdiToothChart` / Tailwind color classes into the capture tree.
+
+| Do | Don't |
+|----|--------|
+| Hex/rgb **inline styles** only in print layout | Tailwind color utilities / CSS variables in capture |
+| [`CaseSheetFdiChart`](frontend/src/components/ui/lab/CaseSheetFdiChart.tsx) (SVG, catalog hex colors) | Reuse interactive `FdiToothChart` for PDF |
+| `onclone`: strip `style` + `link[rel=stylesheet]` | Rely on global stylesheets during capture |
+| Prosthesis labels from **catalog** (then task label) | Fallback `code.replace(/_/g,' ')` alone (breaks casing like `ti base…`) |
+
+### Layout conventions
+
+- Sections: meta → parties → **Prosthesis** rows → **Tooth Chart** heading *above* the horizontal rule → chart → Comments.
+- Connected badge: bold + underline (no border box — html2canvas centering is unreliable).
+- Order number: `externalCode.trim()` when set, else short case id (`id` without hyphens, first 8, uppercased).
+- Share QR when `shareUrl` present.
+
+### API
+
+- `LabCase.externalCode` (optional string, max 64)
+- `PATCH /cases/:id/external-code` `{ externalCode: string | null }` — same edit permission as important flag
+
 ## Live soft refresh
 
 Inbox Socket.IO `notification.created` → `notifyTabBadgesChanged()` → silent `loadCases` + selected `loadDetail` (keeps filters/selection; no full remount). Same event refreshes sidebar Cases badge via `useTabBadgeCounts`. See `.cursor/skills/notifications-inbox/SKILL.md`.