Resolve plural tiers through the i18n context

Importing the plural helper directly from the dashboard trend tile cost
~78 KB gz across the route chunks: the module is tiny, but a new edge
from a widely-instantiated component gets duplicated into every chunk
that contains it rather than hoisted. The provider is already in every
chunk, so expose a plural-aware tCount() there and let components call
that instead. Total client JS goes back under budget.

Also fix the two tests the honest-loading-state change invalidated: the
mental-wellbeing landing tests seeded a never-resolving read and so now
render skeletons rather than instrument cards, and the achievements page
needs a router in scope for its module-gate redirect.

src/__tests__/i18n-reverse-coverage.test.ts

@@ -108,12 +108,14 @@ function collectReferences(
     /(?<![a-zA-Z0-9_])t\(\s*["']([a-zA-Z][a-zA-Z0-9_.-]+)["']/g;
   for (const m of allText.matchAll(literalKeyRe)) literalKeys.add(m[1]);
 
-  // Plural-tier composition: `pluralKey("dashboard.staleHintWeeks", n, locale)`
-  // resolves to `<base>One` / `<base>Few` / `<base>Other` at runtime, so the
-  // base literal accounts for exactly those three leaves and no others. Kept
-  // as an explicit tier list rather than a prefix match so a stray sibling key
-  // under the same base still reports as an orphan.
-  const pluralKeyRe = /pluralKey\(\s*["']([a-zA-Z][a-zA-Z0-9_.-]+)["']/g;
+  // Plural-tier composition: `tCount("dashboard.staleHintWeeks", n)` and the
+  // underlying `pluralKey("…", n, locale)` both resolve to `<base>One` /
+  // `<base>Few` / `<base>Other` at runtime, so the base literal accounts for
+  // exactly those three leaves and no others. Kept as an explicit tier list
+  // rather than a prefix match so a stray sibling key under the same base still
+  // reports as an orphan.
+  const pluralKeyRe =
+    /(?:pluralKey|tCount)\(\s*["']([a-zA-Z][a-zA-Z0-9_.-]+)["']/g;
   for (const m of allText.matchAll(pluralKeyRe)) {
     for (const tier of ["One", "Few", "Other"])
       literalKeys.add(`${m[1]}${tier}`);

src/app/achievements/__tests__/page.test.tsx

@@ -25,6 +25,12 @@ import type { AchievementProgress } from "@/lib/gamification/achievements";
  * matching the `onboarding` page's existing test pattern.
  */
 
+// The page bounces a disabled-module direct hit to /insights (it used to
+// render a blank page), so the SSR render needs a router in scope.
+vi.mock("next/navigation", () => ({
+  useRouter: () => ({ push: vi.fn(), replace: vi.fn(), prefetch: vi.fn() }),
+}));
+
 vi.mock("@/hooks/use-auth", () => ({
   useAuth: () => ({
     isAuthenticated: true,

src/components/charts/trend-card.tsx

@@ -10,7 +10,6 @@ import {
   TooltipTrigger,
 } from "@/components/ui/tooltip";
 import { useTranslations, useFormatters } from "@/lib/i18n/context";
-import { pluralKey } from "@/lib/i18n/plural";
 import type { ComparisonBaseline } from "@/lib/dashboard-layout";
 import {
   getTrendSentiment,
@@ -131,7 +130,7 @@ export function TrendCard({
   emptyHint = null,
   valueAdornment = null,
 }: TrendCardProps) {
-  const { t, locale } = useTranslations();
+  const { t, tCount } = useTranslations();
   const fmt = useFormatters();
 
   // v1.4.33 F5 — pick a single signal to drive both the arrow and the
@@ -371,14 +370,10 @@ export function TrendCard({
               }
               if (staleDays <= 60) {
                 const weeks = Math.floor(staleDays / 7);
-                return t(pluralKey("dashboard.staleHintWeeks", weeks, locale), {
-                  count: weeks,
-                });
+                return tCount("dashboard.staleHintWeeks", weeks);
               }
               const months = Math.floor(staleDays / 30);
-              return t(pluralKey("dashboard.staleHintMonths", months, locale), {
-                count: months,
-              });
+              return tCount("dashboard.staleHintMonths", months);
             })()}
           </span>
         )}

src/components/mental-health/__tests__/mental-wellbeing.test.tsx

@@ -3,6 +3,7 @@ import { renderToStaticMarkup } from "react-dom/server";
 import { QueryClient, QueryClientProvider } from "@tanstack/react-query";
 
 import { I18nProvider } from "@/lib/i18n/context";
+import { queryKeys } from "@/lib/query-keys";
 import en from "../../../../messages/en.json";
 
 /**
@@ -35,6 +36,15 @@ function withProviders(node: React.ReactNode): string {
   const queryClient = new QueryClient({
     defaultOptions: { queries: { retry: false } },
   });
+  // The landing now distinguishes loading from an empty record: while the
+  // history read is in flight it paints skeletons rather than the instrument
+  // cards' "not taken yet" copy, since that copy is a claim about the user's
+  // record. These tests exercise the LOADED landing, so seed the read as a
+  // settled empty result. The failed and in-flight states are covered in
+  // `failed-read-never-empty.test.tsx`.
+  queryClient.setQueryData(queryKeys.mentalHealthAssessments(), {
+    assessments: [],
+  });
   return renderToStaticMarkup(
     <QueryClientProvider client={queryClient}>
       <I18nProvider initialLocale="en">{node}</I18nProvider>

src/lib/i18n/__tests__/t-count.test.tsx

@@ -0,0 +1,64 @@
+import { describe, it, expect } from "vitest";
+import { renderToStaticMarkup } from "react-dom/server";
+
+import { I18nProvider, useTranslations } from "@/lib/i18n/context";
+import type { Locale } from "@/lib/i18n/config";
+
+/**
+ * `tCount` is the plural-aware `t` the components call.
+ *
+ * The tier selection lives on the context rather than in a helper each
+ * component imports, because a new module edge from a widely-instantiated
+ * component duplicates that module into every chunk containing it. That makes
+ * the context the only place the Polish third plural tier is exercised from the
+ * UI, so it needs its own coverage — the pure `pluralTier` tests cannot see a
+ * regression in this wiring.
+ */
+
+function Probe({ base, count }: { base: string; count: number }) {
+  const { tCount } = useTranslations();
+  return <>{tCount(base, count)}</>;
+}
+
+function render(locale: Locale, base: string, count: number): string {
+  return renderToStaticMarkup(
+    <I18nProvider initialLocale={locale}>
+      <Probe base={base} count={count} />
+    </I18nProvider>,
+  );
+}
+
+describe("tCount", () => {
+  it("resolves the Polish few form for 2-4 and the many form for 5+", () => {
+    expect(render("pl", "dashboard.staleHintWeeks", 3)).toBe(
+      "Ostatni odczyt 3 tygodnie temu",
+    );
+    expect(render("pl", "dashboard.staleHintWeeks", 7)).toBe(
+      "Ostatni odczyt 7 tygodni temu",
+    );
+    expect(render("pl", "dashboard.staleHintMonths", 2)).toBe(
+      "Ostatni odczyt 2 miesiące temu",
+    );
+    expect(render("pl", "dashboard.staleHintMonths", 8)).toBe(
+      "Ostatni odczyt 8 miesięcy temu",
+    );
+  });
+
+  it("keeps the singular for 1", () => {
+    expect(render("pl", "dashboard.staleHintWeeks", 1)).toBe(
+      "Ostatni odczyt 1 tydzień temu",
+    );
+    expect(render("en", "dashboard.staleHintWeeks", 1)).toBe(
+      "Last reading 1 week ago",
+    );
+  });
+
+  it("leaves a locale without a few category on its two forms", () => {
+    expect(render("en", "dashboard.staleHintWeeks", 3)).toBe(
+      "Last reading 3 weeks ago",
+    );
+    expect(render("de", "dashboard.staleHintMonths", 3)).toBe(
+      "Letzter Wert vor 3 Monaten",
+    );
+  });
+});

src/lib/i18n/context.tsx

@@ -23,6 +23,7 @@ import { readStoredTimeFormat, subscribeTimeFormat } from "../time-format";
 import { readStoredDateFormat, subscribeDateFormat } from "../date-format";
 import { readStoredTimezone, subscribeTimezone } from "../timezone-mirror";
 import { resolveKey } from "./resolve-key";
+import { pluralKey } from "./plural";
 import {
   getCachedMessages,
   getFallbackMessages,
@@ -42,6 +43,22 @@ interface I18nContextValue {
    */
   pendingLocale: Locale | null;
   t: (key: string, params?: Record<string, string | number>) => string;
+  /**
+   * Plural-aware `t`. Resolves `<baseKey><One|Few|Other>` under the active
+   * locale's CLDR rules and passes `count` through as a parameter.
+   *
+   * Lives on the context rather than as a standalone helper each component
+   * imports: `pluralTier` is tiny, but a new module edge from a
+   * widely-instantiated component (the dashboard trend tile) gets duplicated
+   * into every chunk that contains it, which measured ~78 KB gz across the
+   * route chunks. The provider is already in every chunk, so routing through
+   * it is free.
+   */
+  tCount: (
+    baseKey: string,
+    count: number,
+    params?: Record<string, string | number>,
+  ) => string;
 }
 
 const I18nContext = createContext<I18nContextValue | null>(null);
@@ -281,9 +298,18 @@ export function I18nProvider({
     [locale, messages],
   );
 
+  const tCount = useCallback(
+    (
+      baseKey: string,
+      count: number,
+      params?: Record<string, string | number>,
+    ): string => t(pluralKey(baseKey, count, locale), { count, ...params }),
+    [t, locale],
+  );
+
   const value = useMemo(
-    () => ({ locale, setLocale, pendingLocale, t }),
-    [locale, setLocale, pendingLocale, t],
+    () => ({ locale, setLocale, pendingLocale, t, tCount }),
+    [locale, setLocale, pendingLocale, t, tCount],
   );
 
   return <I18nContext.Provider value={value}>{children}</I18nContext.Provider>;