Manual timezone is the single source of local-time truth (task 7e173881) (#285)

Co-authored-by: dev_agent <dev_agent@cubecraftlabs.com>
Co-committed-by: dev_agent <dev_agent@cubecraftlabs.com>

admin/src/settings/SettingsScreen.test.tsx

@@ -6,6 +6,7 @@ import SettingsScreen, { SCROLL_BOTTOM_PADDING } from "./SettingsScreen";
 import type { AdminChild } from "../api/definitions";
 import type { HouseholdSettings } from "../api/settings";
 import { storeTokens } from "../auth/oidc";
+import { AppTimezoneProvider, useAppTimezone } from "../time/AppTimezone";
 
 const CHILDREN_PATH = "/api/v1/admin/children";
 const REORDER_PATH = `${CHILDREN_PATH}/reorder`;
@@ -23,8 +24,17 @@ const DEFAULT_SETTINGS: HouseholdSettings = {
   end_of_day_report_enabled: true,
   celebration_enabled: false,
   timezone: "America/Chicago",
+  effective_timezone: "America/Chicago",
 };
 
+/** The API host's own zone: the effective zone while none is stored. */
+const API_HOST_ZONE = "Europe/London";
+
+/** The settings as the API answers: `effective_timezone` derived like the API's. */
+function settingsBody(): HouseholdSettings {
+  return { ...settings, effective_timezone: settings.timezone || API_HOST_ZONE };
+}
+
 function child(
   id: number,
   display_name: string,
@@ -82,10 +92,10 @@ async function routeFetch(url: string, init: RequestInit = {}): Promise<Response
     return respond();
   }
   if (path === CHILDREN_PATH && method === "GET") return jsonResponse({ children });
-  if (path === SETTINGS_PATH && method === "GET") return jsonResponse(settings);
+  if (path === SETTINGS_PATH && method === "GET") return jsonResponse(settingsBody());
   if (path === SETTINGS_PATH && method === "PATCH") {
     settings = { ...settings, ...body };
-    return jsonResponse(settings);
+    return jsonResponse(settingsBody());
   }
   if (path === CHILDREN_PATH && method === "POST") {
     const created = child(9, body.display_name, body.sort_order ?? 0, {
@@ -791,3 +801,43 @@ describe("SettingsScreen — manual timezone control", () => {
     }
   });
 });
+
+describe("SettingsScreen — the saved zone applies app-wide", () => {
+  function ZoneProbe() {
+    return <output data-testid="app-zone">{useAppTimezone() || "(browser)"}</output>;
+  }
+
+  beforeEach(() => {
+    sessionStorage.clear();
+    storeTokens({ access_token: "at-123", expires_in: 600 });
+    children = [child(1, "Declan", 1)];
+    settings = { ...DEFAULT_SETTINGS, timezone: "" };
+    writeResponse = null;
+    fetchMock = vi.fn(async (url: string, init?: RequestInit) => routeFetch(url, init));
+    vi.stubGlobal("fetch", fetchMock);
+  });
+
+  afterEach(() => {
+    cleanup();
+    vi.unstubAllGlobals();
+  });
+
+  it("a saved zone becomes the application timezone at once", async () => {
+    render(
+      <AppTimezoneProvider>
+        <ZoneProbe />
+        <SettingsScreen onClose={vi.fn()} />
+      </AppTimezoneProvider>,
+    );
+    const form = await screen.findByRole("form", { name: "Preferences" });
+    // No zone stored: the application runs in the API host's zone.
+    expect(screen.getByTestId("app-zone").textContent).toBe(API_HOST_ZONE);
+
+    fireEvent.change(within(form).getByRole("combobox", { name: "Timezone" }), {
+      target: { value: "America/New_York" },
+    });
+    fireEvent.click(within(form).getByRole("button", { name: "Save preferences" }));
+    await screen.findByText("Preferences saved.");
+    expect(screen.getByTestId("app-zone").textContent).toBe("America/New_York");
+  });
+});

admin/src/settings/SettingsScreen.tsx

@@ -7,7 +7,8 @@
  * Preferences: the household settings (planning horizon, day rollover,
  * timezone, notifications). Save patches only the changed fields. The
  * timezone — the application's source of local time — is only ever set by
- * the admin picking or typing a zone here and saving it.
+ * the admin picking or typing a zone here and saving it; every zone loaded
+ * or saved here is published app-wide (time/AppTimezone.tsx).
  *
  * One write at a time across both sections.
  */
@@ -35,6 +36,7 @@ import {
   type SettingsChanges,
 } from "../api/settings";
 import { FOCUSABLE, inertOutside } from "../schedule/OverrideEditor";
+import { usePublishAppTimezone } from "../time/AppTimezone";
 import { ArrowDownGlyph, ArrowUpGlyph, ChevronLeftGlyph, PlusGlyph } from "./glyphs";
 import "./SettingsScreen.css";
 
@@ -593,6 +595,7 @@ export default function SettingsScreen({ onClose }: { onClose: () => void }) {
   const titleRef = useRef<HTMLHeadingElement>(null);
   const addRef = useRef<HTMLButtonElement>(null);
   const formWasOpen = useRef(false);
+  const publishTimezone = usePublishAppTimezone();
 
   // Modal focus: move in on open, keep the background out of reach, and hand
   // focus back to the opener (the Settings button) on close.
@@ -634,7 +637,9 @@ export default function SettingsScreen({ onClose }: { onClose: () => void }) {
     setPreferences({ kind: "loading" });
     fetchSettings()
       .then((settings) => {
-        if (!cancelled) setPreferences({ kind: "ready", settings });
+        if (cancelled) return;
+        setPreferences({ kind: "ready", settings });
+        publishTimezone(settings.effective_timezone);
       })
       .catch((error: unknown) => {
         if (cancelled) return;
@@ -728,6 +733,7 @@ export default function SettingsScreen({ onClose }: { onClose: () => void }) {
     try {
       const settings = await updateSettings(changes);
       setPreferences({ kind: "ready", settings });
+      publishTimezone(settings.effective_timezone);
       setPreferencesMessage({ kind: "info", text: "Preferences saved." });
     } catch (error) {
       setPreferencesMessage({