diff --git a/.gitignore b/.gitignore
index 132725d27..fe011fcaa 100644
--- a/.gitignore
+++ b/.gitignore
@@ -54,6 +54,7 @@ next-env.d.ts
 # scripts/generate-sw-version.mjs; loaded by public/sw.js to key
 # the cache-version baseline.
 /public/sw-version.js
+/public/i18n/
 
 # v1.4.27 B3 — MaxMind GeoLite2 databases are fetched at build time
 # via `scripts/fetch-geolite2.sh`. Too large for git; license key
diff --git a/e2e/utils/mock-mood-insights.ts b/e2e/utils/mock-mood-insights.ts
index e8dc21e8e..36fe5c144 100644
--- a/e2e/utils/mock-mood-insights.ts
+++ b/e2e/utils/mock-mood-insights.ts
@@ -113,7 +113,10 @@ export async function mockMoodInsights(page: Page): Promise<void> {
     await route.fulfill({
       status: 200,
       contentType: "application/json",
-      body: JSON.stringify({ data: CORRELATION_DISCOVERY_PAYLOAD, error: null }),
+      body: JSON.stringify({
+        data: CORRELATION_DISCOVERY_PAYLOAD,
+        error: null,
+      }),
     });
   });
 }
diff --git a/package.json b/package.json
index 367972474..f20ef9ccc 100644
--- a/package.json
+++ b/package.json
@@ -26,7 +26,8 @@
   "scripts": {
     "prepare": "lefthook install || echo 'lefthook install skipped (no git repo or binary unavailable)'",
     "dev": "next dev",
-    "prebuild": "node scripts/generate-sw-version.mjs",
+    "predev": "node scripts/generate-i18n-boot.mjs",
+    "prebuild": "node scripts/generate-sw-version.mjs && node scripts/generate-i18n-boot.mjs",
     "build": "next build",
     "analyze": "ANALYZE=1 next build",
     "bundle-report": "node scripts/check-bundle-budget.mjs",
diff --git a/scripts/check-bundle-budget.mjs b/scripts/check-bundle-budget.mjs
index 713dfb116..d38c17174 100644
--- a/scripts/check-bundle-budget.mjs
+++ b/scripts/check-bundle-budget.mjs
@@ -150,7 +150,9 @@ const budget = existsSync(BUDGET_PATH)
 
 console.log(`shared baseline (rootMainFiles): ${fmt(rootGz)} gz`);
 console.log(`all client chunks:               ${fmt(totalGz)} gz`);
-console.log(`largest chunk:                   ${fmt(largest.gz)} gz  ${largest.file}`);
+console.log(
+  `largest chunk:                   ${fmt(largest.gz)} gz  ${largest.file}`,
+);
 console.log(`recharts-fingerprint chunks:     ${rechartsChunks}`);
 console.log("");
 
diff --git a/scripts/generate-i18n-boot.mjs b/scripts/generate-i18n-boot.mjs
new file mode 100644
index 000000000..74bd331c0
--- /dev/null
+++ b/scripts/generate-i18n-boot.mjs
@@ -0,0 +1,52 @@
+#!/usr/bin/env node
+/**
+ * Generate the locale-catalog boot scripts (`public/i18n/<locale>.js`).
+ *
+ * The root layout emits `<script src="/i18n/<locale>.js?v=<version>" defer>`
+ * ahead of Next's hydration scripts; the body assigns the active locale's
+ * full message bundle to `self.__HL_I18N`, which `src/lib/i18n/load-locale.ts`
+ * reads in its browser cache initializer. This replaces the former RSC-prop
+ * handoff that serialized the ENTIRE active catalog into every document's
+ * flight payload (392 KB of a 505 KB dashboard HTML, re-downloaded on every
+ * hard load).
+ *
+ * Static `public/` files (rather than a route handler) because Next serves
+ * them with an ETag — repeat loads revalidate to a 304 instead of
+ * re-downloading the catalog — and the service worker caches the versioned
+ * URL cache-first for the offline relaunch. The `?v=` query the layout
+ * appends busts both caches per deploy.
+ *
+ * Runs as a `prebuild`/`predev` step (the `sw-version.js` pattern); output
+ * is gitignored. Content is the same public catalog JSON that ships in the
+ * repository — no tenant data, no secrets.
+ */
+import { mkdirSync, readFileSync, writeFileSync } from "node:fs";
+import { join, dirname } from "node:path";
+import { fileURLToPath } from "node:url";
+
+const __dirname = dirname(fileURLToPath(import.meta.url));
+const repoRoot = join(__dirname, "..");
+const outDir = join(repoRoot, "public", "i18n");
+
+const LOCALES = ["de", "en", "fr", "es", "it", "pl"];
+
+mkdirSync(outDir, { recursive: true });
+
+const banner =
+  "// AUTO-GENERATED by scripts/generate-i18n-boot.mjs — do not edit.\n";
+
+for (const locale of LOCALES) {
+  const messages = JSON.parse(
+    readFileSync(join(repoRoot, "messages", `${locale}.json`), "utf8"),
+  );
+  const payload = JSON.stringify({ locale, messages });
+  writeFileSync(
+    join(outDir, `${locale}.js`),
+    `${banner}self.__HL_I18N = ${payload};\n`,
+    "utf8",
+  );
+}
+
+process.stdout.write(
+  `generate-i18n-boot: wrote ${LOCALES.length} catalogs to public/i18n/\n`,
+);
diff --git a/src/app/i18n/[locale]/route.ts b/src/app/i18n/[locale]/route.ts
deleted file mode 100644
index 244829fcb..000000000
--- a/src/app/i18n/[locale]/route.ts
+++ /dev/null
@@ -1,51 +0,0 @@
-import { NextResponse } from "next/server";
-
-import { locales, type Locale } from "@/lib/i18n/config";
-import { allMessages } from "@/lib/i18n/shared-resolve";
-
-/**
- * Locale-catalog boot script.
- *
- * The root layout emits `<script src="/i18n/<locale>?v=<version>" defer>`
- * ahead of Next's hydration scripts. The body assigns the active locale's
- * full message bundle to `self.__HL_I18N`, which `load-locale.ts` reads in
- * its browser cache initializer — so the first client render holds the same
- * strings the server rendered with.
- *
- * This replaces the former RSC-prop handoff that serialized the ENTIRE
- * active catalog into every document's flight payload (392 KB of a 505 KB
- * dashboard HTML, re-downloaded on every hard load). As a versioned URL the
- * catalog is immutable-cacheable: one download per deploy per locale, then
- * HTTP/SW cache. The `?v=` query is only a cache key; the handler always
- * serves the catalog baked into the running build.
- *
- * Public by design (allowlisted in `src/proxy.ts`): the login page needs it
- * pre-auth, and the catalogs are the same strings that ship in the public
- * repository — no tenant data, no secrets.
- */
-
-const IMMUTABLE_CACHE = "public, max-age=31536000, immutable";
-
-export async function GET(
-  _request: Request,
-  { params }: { params: Promise<{ locale: string }> },
-) {
-  const { locale } = await params;
-  if (!(locales as readonly string[]).includes(locale)) {
-    return new NextResponse(null, { status: 404 });
-  }
-
-  const payload = JSON.stringify({
-    locale,
-    messages: allMessages[locale as Locale],
-  });
-  return new NextResponse(`self.__HL_I18N = ${payload};`, {
-    status: 200,
-    headers: {
-      "Content-Type": "text/javascript; charset=utf-8",
-      "Cache-Control": IMMUTABLE_CACHE,
-      // Belt and suspenders for a script-typed response.
-      "X-Content-Type-Options": "nosniff",
-    },
-  });
-}
diff --git a/src/app/layout.tsx b/src/app/layout.tsx
index c7d841720..07766533c 100644
--- a/src/app/layout.tsx
+++ b/src/app/layout.tsx
@@ -98,7 +98,8 @@ export default async function RootLayout({
           dangerouslySetInnerHTML={{ __html: themeScript }}
         />
         {/*
-          Locale-catalog boot script (see src/app/i18n/[locale]/route.ts).
+          Locale-catalog boot script (generated into public/i18n/ by
+          scripts/generate-i18n-boot.mjs, a prebuild/predev step).
           Replaces the former RSC-prop handoff that inlined the whole
           active catalog into every document's flight payload (392 KB of a
           505 KB dashboard HTML). `defer` keeps it off the parse/paint
@@ -106,12 +107,12 @@ export default async function RootLayout({
           module scripts (both ride the after-parse in-order queue, and
           this tag comes first), so `load-locale.ts` finds `self.__HL_I18N`
           set when the client bundle initializes — SSR text and first
-          client render stay identical. The `?v=` build-version key makes
-          the response immutable-cacheable: one catalog download per
-          deploy, then HTTP/SW cache instead of per-document payload.
+          client render stay identical. Served as a static asset: ETag
+          revalidation (304 on repeat loads) + SW cache-first on the
+          versioned URL replace the per-document payload.
         */}
         <script
-          src={`/i18n/${initialLocale}?v=${process.env.NEXT_PUBLIC_APP_VERSION ?? "dev"}`}
+          src={`/i18n/${initialLocale}.js?v=${process.env.NEXT_PUBLIC_APP_VERSION ?? "dev"}`}
           defer
         />
       </head>
diff --git a/src/components/labs/lab-biomarker-detail.tsx b/src/components/labs/lab-biomarker-detail.tsx
index 978153daf..9c8df503a 100644
--- a/src/components/labs/lab-biomarker-detail.tsx
+++ b/src/components/labs/lab-biomarker-detail.tsx
@@ -55,9 +55,11 @@ import type {
 // loading shell matches the in-card chart footprint so the layout is stable.
 const LabBiomarkerChartLazy = dynamic(
   () =>
-    importWithRetry(() => import("@/components/charts/chart-runtime")).then((mod) => ({
-      default: mod.LabBiomarkerChart,
-    })),
+    importWithRetry(() => import("@/components/charts/chart-runtime")).then(
+      (mod) => ({
+        default: mod.LabBiomarkerChart,
+      }),
+    ),
   { ssr: false, loading: () => <ChartSkeleton /> },
 );
 function LabBiomarkerChart(
@@ -124,7 +126,9 @@ export function LabBiomarkerDetail({ biomarkerId }: { biomarkerId: string }) {
       const localized = t(`labs.catalog.${seed.slug}`).trim().toLowerCase();
       if (localized) map.set(localized, seed.slug);
       const canonical = enBundle
-        ? resolveKey(enBundle, `labs.catalog.${seed.slug}`)?.trim().toLowerCase()
+        ? resolveKey(enBundle, `labs.catalog.${seed.slug}`)
+            ?.trim()
+            .toLowerCase()
         : undefined;
       if (canonical && !map.has(canonical)) map.set(canonical, seed.slug);
     }
diff --git a/src/hooks/__tests__/use-auth-offline-gate.test.ts b/src/hooks/__tests__/use-auth-offline-gate.test.ts
index cb5b54533..1d5c32514 100644
--- a/src/hooks/__tests__/use-auth-offline-gate.test.ts
+++ b/src/hooks/__tests__/use-auth-offline-gate.test.ts
@@ -36,9 +36,9 @@ interface MockQueryState {
 }
 let queryState: MockQueryState;
 vi.mock("@tanstack/react-query", async () => {
-  const actual = await vi.importActual<
-    typeof import("@tanstack/react-query")
-  >("@tanstack/react-query");
+  const actual = await vi.importActual<typeof import("@tanstack/react-query")>(
+    "@tanstack/react-query",
+  );
   return {
     ...actual,
     useQuery: () => ({ ...queryState, refetch: vi.fn() }),
@@ -59,7 +59,12 @@ import {
 const store = new Map<string, string>();
 beforeEach(() => {
   store.clear();
-  queryState = { data: undefined, isError: false, error: null, isLoading: false };
+  queryState = {
+    data: undefined,
+    isError: false,
+    error: null,
+    isLoading: false,
+  };
   vi.stubGlobal("localStorage", {
     getItem: (k: string) => store.get(k) ?? null,
     setItem: (k: string, v: string) => void store.set(k, v),
diff --git a/src/lib/i18n/load-locale.ts b/src/lib/i18n/load-locale.ts
index ef948640a..93265a6ed 100644
--- a/src/lib/i18n/load-locale.ts
+++ b/src/lib/i18n/load-locale.ts
@@ -59,8 +59,8 @@ function initialCache(): Partial<Record<Locale, MessageBundle>> {
     // where a bare require of a TS module throws) — there the cache starts
     // empty and `vitest.setup.ts` primes every bundle up front.
     try {
-      // eslint-disable-next-line @typescript-eslint/no-require-imports
       const { allMessages } =
+        // eslint-disable-next-line @typescript-eslint/no-require-imports
         require("./shared-resolve") as typeof import("./shared-resolve");
       return { ...allMessages };
     } catch {