perf(i18n): stop shipping two full catalogs on every page load

Two independent every-load costs, one per layer:

1. The static EN import in load-locale.ts put the full en.json catalog
   (334 KB raw / ~106 KB gz) into the client JS of EVERY route, for
   every user in every language. No catalog is statically imported by
   client code anymore: the EN fallback floor of the t() chain loads
   lazily on the first actual key miss (the locale-integrity guard
   keeps every locale key-complete, so the miss path is drift-only),
   and the labs biomarker canonical-name lookup fetches EN on demand.

2. The root layout serialized the ENTIRE active-locale catalog into the
   RSC flight payload of every document (392 KB of a 505 KB dashboard
   HTML, re-downloaded on every hard load, uncacheable). The handoff is
   now a versioned, immutable-cacheable boot script
   (/i18n/<locale>?v=<build>, new route handler) that assigns
   self.__HL_I18N before the hydration scripts run, plus a server-side
   cache seed in load-locale.ts behind a typeof-window branch that
   Turbopack compiles out of the browser bundle (verified: zero catalog
   bytes in any client chunk, zero route manifests referencing one).
   SSR text stays correct and the first client render holds the same
   bundle the server rendered with — no EN flash, no hydration drift.

The boot script is public (proxy allowlist: the login page needs it
pre-auth; the body is the same catalog JSON that ships in the public
repo) and cache-first in the service worker, so an offline relaunch
finds it next to the cached shell.

Measured (client-reference manifests, gzip): route JS baseline
/ 391->287 KB gz, /insights 377->273, /measurements 379->275,
/insights/mood 394->290 — the ~104 KB gz EN catalog left every route.

H2

src/components/labs/lab-biomarker-detail.tsx

@@ -1,6 +1,6 @@
 "use client";
 
-import { useMemo, useState } from "react";
+import { useEffect, useMemo, useState } from "react";
 import Link from "next/link";
 import { useRouter } from "next/navigation";
 import {
@@ -27,7 +27,11 @@ import { apiDelete, apiGet } from "@/lib/api/api-fetch";
 import { summarize, type DataSummary } from "@/lib/analytics/trends";
 import { BIOMARKER_CATALOG } from "@/lib/labs/biomarker-catalog";
 import { useTranslations } from "@/lib/i18n/context";
-import { fallbackMessages } from "@/lib/i18n/load-locale";
+import {
+  getFallbackMessages,
+  loadMessages,
+  type MessageBundle,
+} from "@/lib/i18n/load-locale";
 import { resolveKey } from "@/lib/i18n/resolve-key";
 import { queryKeys } from "@/lib/query-keys";
 
@@ -92,23 +96,40 @@ export function LabBiomarkerDetail({ biomarkerId }: { biomarkerId: string }) {
   // marker minted under the English default and then viewed in another locale
   // never matched a map built only from the current locale's names — the rich
   // description silently fell through to the generic line. The English bundle
-  // is always in the client chunk (`fallbackMessages`), so adding its names
-  // makes resolution independent of the locale the marker was created in.
+  // resolves through `getFallbackMessages()` (already in hand on the server
+  // and for EN sessions; lazily fetched below otherwise — the EN catalog is
+  // no longer a static every-route import), so adding its names makes
+  // resolution independent of the locale the marker was created in.
+  const [enBundle, setEnBundle] = useState<MessageBundle | undefined>(
+    getFallbackMessages,
+  );
+  useEffect(() => {
+    if (enBundle) return;
+    let cancelled = false;
+    void loadMessages("en")
+      .then((loaded) => {
+        if (!cancelled) setEnBundle(loaded);
+      })
+      .catch(() => {
+        // Offline — the current-locale names still resolve; only markers
+        // minted under another locale keep the generic description.
+      });
+    return () => {
+      cancelled = true;
+    };
+  }, [enBundle]);
   const slugByName = useMemo(() => {
     const map = new Map<string, string>();
     for (const seed of BIOMARKER_CATALOG) {
       const localized = t(`labs.catalog.${seed.slug}`).trim().toLowerCase();
       if (localized) map.set(localized, seed.slug);
-      const canonical = resolveKey(
-        fallbackMessages,
-        `labs.catalog.${seed.slug}`,
-      )
-        ?.trim()
-        .toLowerCase();
+      const canonical = enBundle
+        ? resolveKey(enBundle, `labs.catalog.${seed.slug}`)?.trim().toLowerCase()
+        : undefined;
       if (canonical && !map.has(canonical)) map.set(canonical, seed.slug);
     }
     return map;
-  }, [t]);
+  }, [t, enBundle]);
   const [addOpen, setAddOpen] = useState(false);
   // Sticky-footer slot for the add-value sheet (the form portals here).
   const [addFooterEl, setAddFooterEl] = useState<HTMLDivElement | null>(null);

src/components/providers.tsx

@@ -182,12 +182,9 @@ function QueryPersistenceBridge() {
 export function Providers({
   children,
   initialLocale,
-  initialMessages,
 }: {
   children: ReactNode;
   initialLocale?: Locale;
-  /** Active locale's bundle, server-resolved by the root layout (RSC handoff). */
-  initialMessages?: Record<string, unknown>;
 }) {
   const [queryClient] = useState(
     () =>
@@ -206,10 +203,7 @@ export function Providers({
   return (
     <QueryClientProvider client={queryClient}>
       <ThemeProvider>
-        <I18nProvider
-          initialLocale={initialLocale}
-          initialMessages={initialMessages}
-        >
+        <I18nProvider initialLocale={initialLocale}>
           <QueryPersistenceBridge />
           <DashboardSnapshotPreloader />
           {children}