perf: stop navigating twice after signing in from the home page

stores/__tests__/auth-store-redirect-after-login.test.ts

@@ -0,0 +1,29 @@
+import { beforeEach, describe, expect, it } from 'vitest';
+import { saveRedirectAfterLogin } from '../auth-store';
+
+// Where login sends the user back to. The app's home is where a login lands
+// anyway; saving it made the login page navigate a second time, to /en/en
+// (the locale-aware router prefixes the locale again), racing the first.
+
+describe('saveRedirectAfterLogin', () => {
+  beforeEach(() => sessionStorage.clear());
+
+  it('saves nothing on the home page, and drops an older target', () => {
+    sessionStorage.setItem('redirect_after_login', '/en/settings');
+    window.history.pushState({}, '', '/en');
+    saveRedirectAfterLogin();
+    expect(sessionStorage.getItem('redirect_after_login')).toBeNull();
+  });
+
+  it('keeps a deep link, query and hash included', () => {
+    window.history.pushState({}, '', '/en/calendar?view=day#e1');
+    saveRedirectAfterLogin();
+    expect(sessionStorage.getItem('redirect_after_login')).toBe('/en/calendar?view=day#e1');
+  });
+
+  it('keeps the home page with a query, which carries a deep link', () => {
+    window.history.pushState({}, '', '/en?email=abc');
+    saveRedirectAfterLogin();
+    expect(sessionStorage.getItem('redirect_after_login')).toBe('/en?email=abc');
+  });
+});

stores/auth-store.ts

@@ -856,6 +856,15 @@ export function saveRedirectAfterLogin(): void {
     const loginPath = getLocaleLoginPath();
     const currentPath = `${window.location.pathname}${window.location.search}${window.location.hash}`;
 
+    // The app's home is where a login lands anyway. Saving it only made the
+    // login page navigate a second time, through the locale-aware router,
+    // which prefixes the locale again (/en/en) and races the first.
+    const home = `${getPathPrefix()}/${getLocaleFromPath()}`;
+    if (currentPath === home || currentPath === `${home}/`) {
+      sessionStorage.removeItem('redirect_after_login');
+      return;
+    }
+
     if (currentPath !== loginPath) {
       sessionStorage.setItem('redirect_after_login', currentPath);
     }