fix(report): pass the in-app locale through to the pdf export

The health-record export panel sent no locale, so the server resolved the
report language from the browser's Accept-Language header. A German user on
an English-default browser got an English doctor report.

Send the active in-app locale from the panel, and on the server resolve
most-specific-first: explicit selection, then the healthlog-locale cookie
(what the user actually chose in the UI), then Accept-Language as the
weakest fallback.

src/app/api/export/health-record/__tests__/route.test.ts

@@ -9,6 +9,7 @@
  */
 import { describe, it, expect, vi, beforeEach } from "vitest";
 import { NextRequest } from "next/server";
+import { PDFParse } from "pdf-parse";
 
 vi.mock("@/lib/db", () => ({
   prisma: {
@@ -38,14 +39,27 @@ const SESSION_OK = {
   user: { id: "user-1", email: "test@example.com", role: "USER" },
 } as const;
 
-function mkReq(body: unknown): NextRequest {
+function mkReq(
+  body: unknown,
+  headers: Record<string, string> = {},
+): NextRequest {
   return new NextRequest("http://localhost/api/export/health-record", {
     method: "POST",
-    headers: { "content-type": "application/json" },
+    headers: { "content-type": "application/json", ...headers },
     body: JSON.stringify(body),
   });
 }
 
+async function pdfText(res: Response): Promise<string> {
+  const bytes = new Uint8Array(await res.arrayBuffer());
+  const parser = new PDFParse({ data: bytes });
+  try {
+    return (await parser.getText()).text;
+  } finally {
+    await parser.destroy();
+  }
+}
+
 beforeEach(() => {
   vi.clearAllMocks();
   vi.mocked(getSession).mockResolvedValue(SESSION_OK as never);
@@ -137,6 +151,46 @@ describe("POST /api/export/health-record — outputs", () => {
     expect(buf.subarray(0, 2).toString("latin1")).toBe("PK");
   });
 
+  it("renders the PDF in the explicit selection locale", async () => {
+    const { POST } = await import("../route");
+    const res = await POST(
+      mkReq({ format: "pdf", locale: "de", practiceName: "Sample Practice" }),
+    );
+    const text = await pdfText(res);
+    // German cover label.
+    expect(text).toContain("Praxis:");
+  });
+
+  it("falls back to the healthlog-locale cookie when no locale is sent", async () => {
+    const { POST } = await import("../route");
+    const res = await POST(
+      mkReq(
+        { format: "pdf", practiceName: "Sample Practice" },
+        {
+          // Browser default English, but the in-app cookie says German — the
+          // cookie must win over Accept-Language.
+          "accept-language": "en-US,en;q=0.9",
+          cookie: "healthlog-locale=de",
+        },
+      ),
+    );
+    const text = await pdfText(res);
+    expect(text).toContain("Praxis:");
+    expect(text).not.toContain("Practice:");
+  });
+
+  it("uses Accept-Language only when neither selection nor cookie is present", async () => {
+    const { POST } = await import("../route");
+    const res = await POST(
+      mkReq(
+        { format: "pdf", practiceName: "Sample Practice" },
+        { "accept-language": "en-US,en;q=0.9" },
+      ),
+    );
+    const text = await pdfText(res);
+    expect(text).toContain("Practice:");
+  });
+
   it("scopes the aggregator measurement read to the session user", async () => {
     const { POST } = await import("../route");
     await POST(mkReq({ format: "fhir", userId: "user-2" } as never));

src/app/api/export/health-record/route.ts

@@ -46,7 +46,7 @@ import {
 } from "@/lib/validations/health-record-export";
 import { getServerTranslator } from "@/lib/i18n/server-translator";
 import { parseLocaleFromAcceptLanguage } from "@/lib/format-locale";
-import { type Locale } from "@/lib/i18n/config";
+import { locales, type Locale } from "@/lib/i18n/config";
 import { resolveUserTimezone } from "@/lib/tz/resolver";
 
 export const POST = apiHandler(async (request: NextRequest) => {
@@ -72,8 +72,20 @@ export const POST = apiHandler(async (request: NextRequest) => {
   const sections = toDoctorReportPrefs(selection.sections);
   const includeCharts = selection.includeCharts ?? true;
 
+  // Locale resolution, most-specific first: the explicit selection wins, then
+  // the in-app `healthlog-locale` cookie (what the user actually chose in the
+  // UI), and only then the browser's Accept-Language header. The header is the
+  // weakest signal — a German user on an English-default browser would
+  // otherwise get an English report.
+  const cookieValue = request.cookies.get("healthlog-locale")?.value;
+  const cookieLocale = (locales as readonly string[]).includes(
+    cookieValue ?? "",
+  )
+    ? (cookieValue as Locale)
+    : null;
   const locale: Locale =
     selection.locale ??
+    cookieLocale ??
     parseLocaleFromAcceptLanguage(
       request.headers.get("accept-language") ?? "",
     );

src/components/settings/health-record-export-panel.tsx

@@ -97,7 +97,7 @@ function buildSelectionSections(s: SectionState) {
 }
 
 export function HealthRecordExportPanel() {
-  const { t } = useTranslations();
+  const { t, locale } = useTranslations();
   const [format, setFormat] = useState<ExportFormat>("pdf");
   const [days, setDays] = useState<number>(90);
   const [practiceName, setPracticeName] = useState("");
@@ -140,6 +140,10 @@ export function HealthRecordExportPanel() {
         credentials: "include",
         body: JSON.stringify({
           format,
+          // Carry the active in-app locale so the generated artefact matches
+          // the UI language instead of falling back to the browser's
+          // Accept-Language header on the server.
+          locale,
           range: { days },
           practiceName: practiceName.trim() || undefined,
           includeCharts,