fix(dashboard): activate fallback locale before extensions

Dashboard extensions can evaluate translation calls before the asynchronous default catalog finishes loading. Activate an empty source-locale catalog synchronously so extension imports and compiled catalog loading remain parallel without triggering Lingui's missing-locale error.

Author: dlhck

packages/dashboard/src/lib/framework/extension-api/use-dashboard-extensions.spec.tsx

@@ -0,0 +1,64 @@
+import { i18n } from '@lingui/core';
+import { act } from 'react';
+import { createRoot } from 'react-dom/client';
+import { afterEach, beforeEach, describe, expect, it, vi } from 'vitest';
+
+import { defaultLocale } from '../../providers/i18n-provider.js';
+import { useDashboardExtensions } from './use-dashboard-extensions.js';
+
+const runDashboardExtensions = vi.hoisted(() => vi.fn());
+
+(globalThis as typeof globalThis & { IS_REACT_ACT_ENVIRONMENT: boolean }).IS_REACT_ACT_ENVIRONMENT = true;
+
+vi.mock('virtual:dashboard-extensions', () => ({
+    runDashboardExtensions,
+}));
+
+vi.mock('./define-dashboard-extension.js', () => ({
+    onExtensionSourceChange: vi.fn(),
+}));
+
+describe('useDashboardExtensions', () => {
+    let container: HTMLDivElement;
+    let root: ReturnType<typeof createRoot>;
+
+    beforeEach(() => {
+        container = document.createElement('div');
+        document.body.appendChild(container);
+        root = createRoot(container);
+    });
+
+    afterEach(async () => {
+        await act(async () => {
+            root.unmount();
+        });
+        container.remove();
+        vi.clearAllMocks();
+    });
+
+    it('can evaluate translations before the full locale catalog has loaded', async () => {
+        let extensionError: unknown;
+
+        runDashboardExtensions.mockImplementation(async () => {
+            try {
+                const extensionMessageId = ['Extension', 'label'].join(' ');
+                i18n._(extensionMessageId);
+            } catch (error) {
+                extensionError = error;
+            }
+        });
+
+        function DashboardBootstrap() {
+            useDashboardExtensions();
+            return null;
+        }
+
+        await act(async () => {
+            root.render(<DashboardBootstrap />);
+        });
+
+        expect(runDashboardExtensions).toHaveBeenCalledOnce();
+        expect(i18n.locale).toBe(defaultLocale);
+        expect(extensionError).toBeUndefined();
+    });
+});

packages/dashboard/src/lib/providers/i18n-provider.tsx

@@ -5,6 +5,13 @@ import React from 'react';
 
 export const defaultLocale = 'en';
 
+// Dashboard extensions are evaluated asynchronously during app bootstrap and
+// may translate source-locale strings at module scope. Activate an empty source
+// catalog synchronously so those translations are safe while the compiled
+// dashboard and plugin catalogs load in parallel.
+i18n.load(defaultLocale, {});
+i18n.activate(defaultLocale);
+
 /**
  * We do a dynamic import of just the catalog that we need
  * @param locale any locale string