@@ -39,7 +39,7 @@ Each feature file starts with an H1 title and one paragraph describing the user-
 
 ## Features
 
-- [Demo-code sign-in](./auth-demo-login.md): sign-in, reload, rejected code, sign-out (`e2e/full-stack/auth.spec.ts`); email one-time-code sign-in through Mailpit, the emailed sign-in link through `/auth/callback` (including after a failed resend, and a used link), and a second account on the same browser (`recipes/auth.spec.ts`).
+- [Demo-code sign-in](./auth-demo-login.md): sign-in, reload, rejected code, sign-out (`e2e/full-stack/auth.spec.ts`); email one-time-code sign-in through Mailpit, the emailed sign-in link through `/auth/callback` (including after a failed resend, and a used link), a signed-out deep link through a wrong code, the resend countdown and back, and a second account on the same browser (`recipes/auth.spec.ts`).
 - [Case generation](./case-generation.md): generate, web research, save and reopen from History on a fresh device, PDF and DOCX export, single-section regeneration, building a flowchart from the case, provider failure and retry, a reply cut off at its length cap, quota block (`recipes/case-generation.spec.ts`).
 - [Library sources](./library-sources.md): add, pause, delete, grounding, and URL import (`recipes/library.spec.ts`).
 - [AI tools](./ai-tools.md): Attack, Brainstorm, Factoids, and Ask streamed, cut off at its length cap, cited, and with web search (`recipes/ai-tools.spec.ts`).
 
@@ -11,6 +11,7 @@ A visitor signs in with a demo access code on the Login page. The `demo-code-log
 - `auth-refresh` refreshes an expired access token before an AI request.
 - `auth-session-expired` signs out a session the server revoked: the stored tokens are refused, so the app goes to `/login` and shows `Your session expired. Sign in again.` once (`recipes/auth.spec.ts`).
 - `auth-email-link` opens the sign-in link from the email after a resend failed with 429. It lands on `/app` through `/auth/callback` without showing `/login` on the way, and the same link opened again shows `This sign-in link has expired or was already used. Send a new code.` on `/login` (`recipes/auth.spec.ts`).
+- `auth-deep-link-email-code` opens `/app/generate` signed out, lands on `/login` (one `main`, an `h1`), sends a code, and sees `Resend in 0:NN` disabled. A wrong code shows `That code is wrong or has expired. Check it or send a new one.`. After the countdown it resends (`New code sent`, the old error gone), and the new code returns to `/app/generate` (`recipes/auth.spec.ts`).
 - `auth-switch-account` signs out from Settings (the logout request has `scope=local`) and signs a second account in on the same `/login` page. It lands on `/app`, not on Settings, and gets its own onboarding tour. On phones the menu still opens and navigates while the tour shows (`recipes/auth.spec.ts`).
 
 ## How to get to it (user POV)
@@ -30,6 +31,7 @@ Preconditions:
 - **Reject.** On a signed-out page, submit `DEMO-ZZZZ-ZZZZ`. The element with role `alert` has the text `Demo code not found.`, and the URL still matches `/login`.
 - **Sign out.** On `/app/settings`, click the button named `Sign out`, then go to `/app/generate`. The URL matches `/login`.
 - **Email link.** Local email templates are code-only, so the recipe builds the link prod's email carries: `${LOCAL_SUPABASE_URL}/auth/v1/verify?token=pkce_<sha224(email + code)>&type=magiclink&redirect_to=<redirect_to of the /auth/v1/otp request>`. The `redirect_to` is `http://127.0.0.1:18081/auth/callback?sb_flow_id=<32 hex>`. Route `**/auth/v1/otp**` to a 429 before clicking `Resend code` to reproduce the failed resend.
+- **Resend countdown.** After each send, `Resend code` is disabled and named `Resend in 0:NN` for a minute (or as long as a 429 asked). The deadline is in sessionStorage under `debatelab:otp-resend-until:<email>`; set it to `0` to end the wait, and the button turns back within a second (`expireResendCooldown` in `recipes/auth.spec.ts`). Sending again to the same address before then opens the code step without a request.
 - **Switch account.** After `Sign out`, sign the second account in on the same `/login` page. `page.goto("/login")` drops the history state that the bug depended on. Create the second user with `createDemoUser` and delete it in `finally`.
 - **Revoked session.** Signed in on `/app`, replace `access_token` in the `debate-auth-local` localStorage entry with a JWT the server refuses, `refresh_token` with `x`, and `expires_at` with now + 3000 s, then reload. Within a few seconds the URL matches `/login` and a `status` element says `Your session expired. Sign in again.`. A second reload no longer shows it.
 
 
@@ -8,8 +8,8 @@ import { createDemoUser, debateControl, deleteDemoUser, expect, test } from "./f
 const mailer = process.env.WORKSPACE_TEST_MAILER_URL;
 const supabaseUrl = process.env.LOCAL_SUPABASE_URL;
 
-/** Reads the six-digit code sent to `email` after `sentAfter` from the local Mailpit inbox. */
-async function readOtp(request: APIRequestContext, email: string, sentAfter: number) {
+/** Reads the six-digit code sent to `email` after `sentAfter` from the local Mailpit inbox; `not` skips an older code. */
+async function readOtp(request: APIRequestContext, email: string, sentAfter: number, not?: string) {
   let otp = "";
   await expect.poll(async () => {
     const payload = await (await request.get(`${mailer}/api/v1/messages`)).json() as { messages?: Array<Record<string, unknown>> };
@@ -18,13 +18,25 @@ async function readOtp(request: APIRequestContext, email: string, sentAfter: num
       if (Date.parse(String(message.Created ?? 0)) < sentAfter - 5_000) continue;
       const detail = await (await request.get(`${mailer}/api/v1/message/${message.ID}`)).text();
       otp = detail.match(/\b(\d{6})\b/)?.[1] ?? "";
+      if (otp === not) otp = "";
       if (otp) break;
     }
     return otp;
   }, { timeout: 30_000 }).toMatch(/^\d{6}$/);
   return otp;
 }
 
+/**
+ * Ends the Resend countdown (AUTH-04) without waiting a minute. LoginPage reads
+ * the stored deadline every second, so the button turns back within one tick.
+ */
+async function expireResendCooldown(page: Page) {
+  await page.evaluate(() => {
+    for (const key of Object.keys(sessionStorage)) if (key.startsWith("debatelab:otp-resend-until:")) sessionStorage.setItem(key, "0");
+  });
+  await expect(page.getByRole("button", { name: "Resend code" })).toBeEnabled({ timeout: 3_000 });
+}
+
 /** Every path this tab shows, kept across reloads, so a flash of /login is caught. */
 async function recordPaths(page: Page) {
   await page.addInitScript(() => {
@@ -114,6 +126,8 @@ test("auth-email-link: the emailed sign-in link signs in after a failed resend,
   await evidence.step(`Sent a code; the link returns to ${redirectTo.replace(/sb_flow_id=.*/, "sb_flow_id=<flow>")}`);
 
   // AUTH-01: the resend hits Auth's rate limit, and auth-js drops that resend's verifier.
+  await expect(page.getByRole("button", { name: /^Resend in 0:\d\d$/ })).toBeDisabled();
+  await expireResendCooldown(page);
   await page.route("**/auth/v1/otp**", (route) => route.fulfill({
     status: 429,
     contentType: "application/json",
@@ -156,6 +170,46 @@ test("auth-email-link: the emailed sign-in link signs in after a failed resend,
   await evidence.step("Opened the used link again; /login says it expired or was used");
 });
 
+test("auth-deep-link-email-code: a signed-out deep link signs in by email code and returns to the page", async ({ page, user, request, evidence }) => {
+  test.skip(!mailer, "WORKSPACE_TEST_MAILER_URL is missing; run through verify.sh drive");
+  // AUTH-14 and AX-06: the deep link goes to /login, which has one <main> and an <h1>.
+  await page.goto("/app/generate");
+  await expect(page).toHaveURL(/\/login$/);
+  await expect(page.getByRole("main")).toHaveCount(1);
+  await expect(page.getByRole("heading", { level: 1, name: "Sign in to DebateLab" })).toBeVisible();
+  await evidence.aria("01-login-from-deep-link");
+
+  let sentAfter = Date.now();
+  await page.getByLabel("Email address").fill(user.email);
+  await page.getByRole("button", { name: "Send code" }).click();
+  await expect(page.getByText("Code sent", { exact: true })).toBeVisible();
+  // AUTH-04: Resend waits out Auth's minimum gap, and says how long.
+  await expect(page.getByRole("button", { name: /^Resend in 0:\d\d$/ })).toBeDisabled();
+  await evidence.shot("02-code-sent-countdown");
+  const firstOtp = await readOtp(request, user.email, sentAfter);
+
+  // AUTH-03: real Auth answers otp_expired for a wrong code; the message says it may be wrong.
+  await page.getByRole("textbox", { name: "Verification code" }).fill(firstOtp === "000000" ? "111111" : "000000");
+  await page.getByRole("button", { name: "Verify code" }).click();
+  await expect(page.getByRole("alert")).toHaveText("That code is wrong or has expired. Check it or send a new one.");
+  await evidence.shot("03-wrong-code");
+
+  // AUTH-05: a new send clears the old error.
+  await expireResendCooldown(page);
+  sentAfter = Date.now();
+  await page.getByRole("button", { name: "Resend code" }).click();
+  await expect(page.getByText("New code sent", { exact: true })).toBeVisible();
+  await expect(page.getByRole("alert")).toHaveCount(0);
+  const otp = await readOtp(request, user.email, sentAfter, firstOtp);
+  await evidence.step("Wrong code refused, countdown ended, a new code sent");
+
+  await page.getByRole("textbox", { name: "Verification code" }).fill(otp);
+  await page.getByRole("button", { name: "Verify code" }).click();
+  await expect(page).toHaveURL(/\/app\/generate$/, { timeout: 20_000 });
+  await evidence.shot("04-back-on-generate");
+  await evidence.step("Signed in by email code and returned to /app/generate");
+});
+
 test("auth-switch-account: the next account on this browser starts on /app, gets its own tour, and sign-out stays local", async ({ signedIn: page, evidence }, testInfo) => {
   const second = await createDemoUser(`${testInfo.project.name}-second`);
   try {
 
@@ -1,12 +1,14 @@
 import { useEffect, useRef } from 'react';
 import { Navigate, useLocation } from 'react-router-dom';
+import { useTranslation } from 'react-i18next';
 import { useAuth } from '@/lib/supabase/AuthProvider';
 import { Loader2 } from 'lucide-react';
 import { consumeWorkspaceInvite, stashWorkspaceInvite } from '@/lib/workspace/invite-handoff';
 
 export function RequireAuth({ children }: { children: React.ReactNode }) {
   const { user, loading } = useAuth();
   const location = useLocation();
+  const { t } = useTranslation();
   // The account this layout last showed. A sign-out here stamps the redirect
   // with it, so LoginPage returns only that account to the page it left.
   const lastUserId = useRef<string | undefined>(undefined);
@@ -15,10 +17,14 @@ export function RequireAuth({ children }: { children: React.ReactNode }) {
   }, [user]);
 
   if (loading) {
+    // Signed-out views have no AppLayout, so this is the page's one <main>.
     return (
-      <div className="min-h-screen flex items-center justify-center bg-background">
-        <Loader2 className="h-8 w-8 animate-spin text-primary" />
-      </div>
+      <main className="min-h-screen flex items-center justify-center bg-background">
+        <div role="status">
+          <Loader2 className="h-8 w-8 animate-spin text-primary" aria-hidden="true" />
+          <span className="sr-only">{t('common.loading')}</span>
+        </div>
+      </main>
     );
   }
 
 
@@ -1,4 +1,5 @@
 import type { TFunction } from 'i18next';
+import { formatWait } from '@/lib/login-form';
 
 // Server messages from the demo-code-login Edge Function, mapped to catalog keys.
 const DEMO_CODE_MESSAGES: Record<string, string> = {
@@ -15,11 +16,27 @@ const DEMO_CODE_MESSAGES: Record<string, string> = {
 const AUTH_CODES: Record<string, string> = {
   over_email_send_rate_limit: 'login.errors.rateLimited',
   over_request_rate_limit: 'login.errors.rateLimited',
+  // Auth answers otp_expired for a mistyped code too, so the message covers both.
   otp_expired: 'login.errors.codeExpired',
   email_address_invalid: 'login.invalidEmail',
   validation_failed: 'login.invalidEmail',
 };
 
+// Auth's max_frequency refusal: "For security purposes, you can only request this after 42 seconds."
+const RETRY_AFTER = /\bafter (\d{1,5}) seconds?\b/i;
+
+/**
+ * Seconds Auth asked to wait before sending another email, when its refusal says so.
+ * Null for any other error, and for limits that name no wait (the hourly email cap).
+ */
+export function authRetryAfterSeconds(error: unknown): number | null {
+  if (!(error instanceof Error)) return null;
+  const { code, status } = error as Error & { code?: unknown; status?: unknown };
+  if (status !== 429 && code !== 'over_email_send_rate_limit' && code !== 'over_request_rate_limit') return null;
+  const match = RETRY_AFTER.exec(error.message);
+  return match ? Number(match[1]) : null;
+}
+
 /**
  * Turns a sign-in failure into a message in the user's language. Unknown errors get the
  * caller's fallback instead of raw English from the backend.
@@ -29,6 +46,9 @@ export function localizeAuthError(error: unknown, t: TFunction, fallbackKey: str
     const demoKey = DEMO_CODE_MESSAGES[error.message.trim()];
     if (demoKey) return t(demoKey, error.message);
 
+    const wait = authRetryAfterSeconds(error);
+    if (wait !== null) return t('login.errors.rateLimitedWait', { time: formatWait(wait) });
+
     const { code, status } = error as Error & { code?: unknown; status?: unknown };
     if (typeof code === 'string' && AUTH_CODES[code]) return t(AUTH_CODES[code]);
     if (status === 429) return t('login.errors.rateLimited');
 
@@ -0,0 +1,94 @@
+// Input rules and the resend cooldown for LoginPage's email and demo-code forms.
+
+const EMAIL_PATTERN = /^[^\s@]+@[^\s@]+\.[^\s@]+$/;
+// RFC 5321's limit on a forward-path, which Auth enforces too.
+export const EMAIL_MAX_LENGTH = 254;
+
+export type EmailProblem = 'required' | 'tooLong' | 'invalid';
+
+/** Why `email` (already trimmed) can't be sent, or null when it can. */
+export function emailProblem(email: string): EmailProblem | null {
+  if (!email) return 'required';
+  if (email.length > EMAIL_MAX_LENGTH) return 'tooLong';
+  return EMAIL_PATTERN.test(email) ? null : 'invalid';
+}
+
+export const DEMO_CODE_PATTERN = /^DEMO-[A-Z0-9]{4}-[A-Z0-9]{4}$/;
+
+/**
+ * Shapes what someone types or pastes into `DEMO-XXXX-XXXX`: uppercase, letters
+ * and digits only, with the prefix and dashes put in for them. A dash appears only
+ * before a character, so Backspace over a trailing dash is never undone.
+ */
+export function formatDemoCode(value: string): string {
+  const chars = value.toUpperCase().replace(/[^A-Z0-9]/g, '');
+  // Still typing the prefix itself.
+  if ('DEMO'.startsWith(chars)) return chars;
+  const body = (chars.startsWith('DEMO') ? chars.slice(4) : chars).slice(0, 8);
+  return `DEMO-${body.slice(0, 4)}${body.length > 4 ? `-${body.slice(4)}` : ''}`;
+}
+
+const alnumCount = (value: string) => value.toUpperCase().replace(/[^A-Z0-9]/g, '').length;
+
+/**
+ * formatDemoCode, plus where the caret goes: after the same letter or digit it
+ * followed before, so an edit mid-code doesn't throw it to the end.
+ */
+export function formatDemoCodeAt(value: string, caret: number): { value: string; caret: number } {
+  const formatted = formatDemoCode(value);
+  let before = alnumCount(value.slice(0, caret));
+  // The prefix was added for them: its four letters come before the caret too.
+  if (formatted.startsWith('DEMO-') && !value.toUpperCase().replace(/[^A-Z0-9]/g, '').startsWith('DEMO')) before += 4;
+  let position = 0;
+  for (let seen = 0; position < formatted.length && seen < before; position += 1) {
+    if (/[A-Z0-9]/.test(formatted[position])) seen += 1;
+  }
+  return { value: formatted, caret: position };
+}
+
+// Auth's own minimum gap between two emails to one address (max_frequency).
+export const RESEND_COOLDOWN_SECONDS = 60;
+const COOLDOWN_KEY = 'debatelab:otp-resend-until:';
+// Used when sessionStorage refuses writes, so the cooldown still holds on this page.
+const memoryCooldowns = new Map<string, number>();
+
+function cooldownKey(email: string): string {
+  return `${COOLDOWN_KEY}${email.trim().toLowerCase()}`;
+}
+
+/** Starts the wait before another code can be sent to `email`. Kept for this tab, across reloads. */
+export function startResendCooldown(email: string, seconds = RESEND_COOLDOWN_SECONDS, now = Date.now()): void {
+  const until = now + seconds * 1000;
+  try {
+    sessionStorage.setItem(cooldownKey(email), String(until));
+  } catch {
+    // Storage is full or blocked; the cooldown then lasts until a reload.
+    memoryCooldowns.set(cooldownKey(email), until);
+  }
+}
+
+/** Whole seconds left before another code can be sent to `email`; 0 when it can be sent now. */
+export function resendCooldownSeconds(email: string, now = Date.now()): number {
+  let until: number;
+  try {
+    until = Number(sessionStorage.getItem(cooldownKey(email)) ?? memoryCooldowns.get(cooldownKey(email)) ?? 0);
+  } catch {
+    until = memoryCooldowns.get(cooldownKey(email)) ?? 0;
+  }
+  const seconds = Number.isFinite(until) ? Math.ceil((until - now) / 1000) : 0;
+  if (seconds > 0) return Math.min(seconds, 60 * 60); // Capped, so a bad stored value can't lock the button for good.
+  // Over: the address needn't stay in storage.
+  memoryCooldowns.delete(cooldownKey(email));
+  try {
+    sessionStorage.removeItem(cooldownKey(email));
+  } catch {
+    // Nothing stored.
+  }
+  return 0;
+}
+
+/** `0:59`, `1:05`: how a wait reads on the Resend button and in errors. */
+export function formatWait(seconds: number): string {
+  const whole = Math.max(0, Math.ceil(seconds));
+  return `${Math.floor(whole / 60)}:${String(whole % 60).padStart(2, '0')}`;
+}
@@ -548,9 +548,13 @@
     "emailHint": "We'll send a six-digit code.",
     "sendCode": "Send code",
     "sendingCode": "Sending code...",
+    "slowSend": "This can take a few seconds.",
     "resendCode": "Resend code",
     "resendingCode": "Resending code...",
+    "resendIn": "Resend in {{time}}",
     "codeSent": "Code sent",
+    "codeResent": "New code sent",
+    "codeRecentlySent": "We sent a code to this address a moment ago. Enter it below, or resend when the timer ends.",
     "codeSentDesc": "Check your email for the six-digit code.",
     "useDifferentEmail": "Use a different email",
     "otpLabel": "Verification code",
@@ -566,8 +570,12 @@
     "retrySignIn": "Try again",
     "backToSignIn": "Back to sign-in",
     "invalidEmail": "Enter a valid email address.",
+    "emailRequired": "Email is required.",
+    "emailTooLong": "That email address is too long. Use one with at most {{max}} characters.",
     "invalidCode": "Enter a valid six-digit code.",
     "invalidDemoCode": "Enter a valid demo code.",
+    "demoCodeRequired": "Enter your demo code.",
+    "invalidDemoCodeFormat": "Demo codes look like DEMO-AB12-CD34.",
     "emailOtpError": "Could not send code.",
     "verifyOtpError": "Could not verify code.",
     "demoError": "Could not sign in with demo code.",
@@ -584,6 +592,7 @@
       "demoExpired": "This demo code has expired.",
       "demoUsedUp": "This demo code has no uses left.",
       "rateLimited": "Too many attempts. Try again later.",
+      "rateLimitedWait": "Too many attempts. Try again in {{time}}.",
       "codeExpired": "That code is wrong or has expired. Check it or send a new one.",
       "network": "Can't reach DebateLab. Check your connection and try again.",
       "linkExpired": "This sign-in link has expired or was already used. Send a new code.",