diff --git a/docs/api/openapi.yaml b/docs/api/openapi.yaml
index 79e597122..4055a7446 100644
--- a/docs/api/openapi.yaml
+++ b/docs/api/openapi.yaml
@@ -1354,8 +1354,15 @@ paths:
       tags:
         - Auth
       summary: Email-or-username login (password)
-      description: "Browser callers receive a session cookie. Native callers (X-Client-Type: native or HealthLog-iOS UA
-        prefix) additionally receive a paired access + refresh token."
+      description: >-
+        Browser callers receive a session cookie. Native callers (X-Client-Type: native or HealthLog-iOS UA prefix)
+        additionally receive a paired access + refresh token.
+
+
+        v1.23 — when the account has a confirmed second factor, the response carries no session/token. It returns HTTP
+        200 with `data: null, error: null` and `meta.mfaRequired: true` plus a single-use `meta.mfaTicket` and the
+        `meta.methods` list. The client must POST the ticket + a code to `/api/auth/mfa/verify` to obtain the token
+        bundle. Accounts without MFA are unchanged.
       requestBody:
         required: true
         content:
@@ -1374,11 +1381,124 @@ paths:
                 - password
       responses:
         "200":
-          description: Login succeeded.
+          description: Login succeeded (token bundle / cookie) — or a second factor is required (`meta.mfaRequired`).
           content:
             application/json:
               schema:
-                $ref: "#/components/schemas/LoginResponse"
+                anyOf:
+                  - $ref: "#/components/schemas/LoginResponse"
+                  - $ref: "#/components/schemas/MfaRequiredResponse"
+        "401": *a1
+        "422": *a3
+        "429": *a4
+  /api/auth/mfa/verify:
+    post:
+      tags:
+        - Auth
+      summary: Complete a second-factor login challenge
+      description: Presents the `mfaTicket` from the login `meta.mfaRequired` response plus a TOTP or recovery code. On
+        success returns the SAME token bundle / session the password path issues, with the session marked
+        second-factor-verified. The ticket is single-use; wrong codes are throttled and the ticket is burned at the
+        attempt cap.
+      requestBody:
+        required: true
+        content:
+          application/json:
+            schema:
+              $ref: "#/components/schemas/MfaVerifyRequest"
+      responses:
+        "200":
+          description: Second factor verified — session + optional bearer issued.
+          content:
+            application/json:
+              schema:
+                $ref: "#/components/schemas/MfaVerifyResponse"
+        "401": *a1
+        "422": *a3
+        "429": *a4
+  /api/auth/me/mfa/totp/setup:
+    post:
+      tags:
+        - Auth
+      summary: Begin TOTP enrollment (cookie session only)
+      description: Generates and stores a pending (encrypted) TOTP secret and returns the otpauth URI + Base32 secret. MFA is
+        not active until /confirm. Cookie-only — a Bearer token cannot enrol MFA.
+      responses:
+        "200":
+          description: Pending secret created.
+          content:
+            application/json:
+              schema:
+                $ref: "#/components/schemas/TotpSetupEnvelope"
+        "401": *a1
+        "422": *a3
+        "429": *a4
+  /api/auth/me/mfa/totp/confirm:
+    post:
+      tags:
+        - Auth
+      summary: Confirm TOTP enrollment (cookie session only)
+      description: Verifies a code against the pending secret, activates the factor, and returns the one-time recovery codes.
+        Cookie-only.
+      requestBody:
+        required: true
+        content:
+          application/json:
+            schema:
+              type: object
+              properties:
+                code:
+                  type: string
+                  pattern: ^\d{6}$
+              required:
+                - code
+      responses:
+        "200":
+          description: Factor activated — recovery codes returned once.
+          content:
+            application/json:
+              schema:
+                $ref: "#/components/schemas/TotpConfirmEnvelope"
+        "401": *a1
+        "422": *a3
+        "429": *a4
+  /api/auth/me/mfa/disable:
+    post:
+      tags:
+        - Auth
+      summary: Disable the second factor (step-up gated)
+      description: Requires a fresh second-factor step-up (cookie session) AND a current TOTP or recovery code. Clears the
+        secret and deletes recovery codes. Bearer can never satisfy the step-up gate.
+      requestBody:
+        required: true
+        content:
+          application/json:
+            schema:
+              $ref: "#/components/schemas/MfaDisableRequest"
+      responses:
+        "200":
+          description: Factor disabled.
+          content:
+            application/json:
+              schema:
+                $ref: "#/components/schemas/MfaDisableEnvelope"
+        "401": *a1
+        "422": *a3
+        "429": *a4
+  /api/auth/me/mfa/recovery-codes/regenerate:
+    post:
+      tags:
+        - Auth
+      summary: Regenerate recovery codes (step-up gated)
+      description: Invalidates the entire prior recovery-code set and returns a fresh batch once. Step-up gated; Bearer can
+        never satisfy the gate.
+      responses:
+        "200":
+          description: Fresh recovery codes issued.
+          content:
+            application/json:
+              schema:
+                $ref: "#/components/schemas/MfaRecoveryRegenEnvelope"
         "401": *a1
         "422": *a3
         "429": *a4
@@ -7492,6 +7612,43 @@ paths:
         "429": *a4
 components:
   schemas:
+    MfaVerifyRequest:
+      type: object
+      properties:
+        mfaTicket:
+          type: string
+          minLength: 1
+          description: The opaque single-use ticket from the login response.
+        method:
+          default: totp
+          type: string
+          enum:
+            - totp
+            - recovery
+        code:
+          type: string
+          minLength: 6
+          maxLength: 32
+      required:
+        - mfaTicket
+        - code
+      description: Complete a second-factor login challenge and receive the same token bundle the password path issues.
+    MfaDisableRequest:
+      type: object
+      properties:
+        code:
+          type: string
+          minLength: 6
+          maxLength: 32
+        method:
+          default: totp
+          type: string
+          enum:
+            - totp
+            - recovery
+      required:
+        - code
+      description: Disable the second factor. Requires fresh step-up plus a current TOTP or recovery code.
     PasskeyLoginVerifyRequest:
       type: object
       properties:
@@ -10660,6 +10817,166 @@ components:
         - tokenExpiresAt
       additionalProperties: false
       description: Native-client token bundle returned by login + refresh. Web cookie-only callers see only `user`.
+    MfaRequiredResponse:
+      type: object
+      properties:
+        data:
+          type: "null"
+        error:
+          type: "null"
+        meta:
+          type: object
+          properties:
+            mfaRequired:
+              type: boolean
+              const: true
+            mfaTicket:
+              type: string
+              description: Opaque, single-use, ~5-minute ticket to present to /api/auth/mfa/verify.
+            methods:
+              type: array
+              items:
+                type: string
+                enum:
+                  - totp
+                  - recovery
+              description: Second factors the account can complete the challenge with.
+          required:
+            - mfaRequired
+            - mfaTicket
+            - methods
+          additionalProperties: false
+      required:
+        - data
+        - error
+        - meta
+      additionalProperties: false
+      description: Password accepted but a second factor is required. Not an error and not a session — no token is issued
+        until /api/auth/mfa/verify succeeds.
+    MfaVerifyResponse:
+      type: object
+      properties:
+        data:
+          $ref: "#/components/schemas/AccessRefreshBundle"
+        error:
+          type: "null"
+        meta:
+          type: object
+          properties:
+            requestId:
+              type: string
+          additionalProperties: false
+      required:
+        - data
+        - error
+      additionalProperties: false
+    TotpSetupEnvelope:
+      type: object
+      properties:
+        data:
+          $ref: "#/components/schemas/TotpSetupResponse"
+        error:
+          type: "null"
+        meta:
+          type: object
+          properties:
+            requestId:
+              type: string
+          additionalProperties: false
+      required:
+        - data
+        - error
+      additionalProperties: false
+    TotpSetupResponse:
+      type: object
+      properties:
+        otpauthUri:
+          type: string
+          description: otpauth:// URI to render as a QR code (carries the secret).
+        totpSecret:
+          type: string
+          description: Base32 secret for manual entry. Pending until confirmed.
+      required:
+        - otpauthUri
+        - totpSecret
+      additionalProperties: false
+    TotpConfirmEnvelope:
+      type: object
+      properties:
+        data:
+          $ref: "#/components/schemas/MfaRecoveryCodesResponse"
+        error:
+          type: "null"
+        meta:
+          type: object
+          properties:
+            requestId:
+              type: string
+          additionalProperties: false
+      required:
+        - data
+        - error
+      additionalProperties: false
+    MfaRecoveryCodesResponse:
+      type: object
+      properties:
+        enabled:
+          type: boolean
+        recoveryCodes:
+          type: array
+          items:
+            type: string
+          description: Single-use recovery codes, shown once. Save them now.
+        recoveryCodesRemaining:
+          type: integer
+          minimum: -9007199254740991
+          maximum: 9007199254740991
+      required:
+        - recoveryCodes
+        - recoveryCodesRemaining
+      additionalProperties: false
+    MfaDisableEnvelope:
+      type: object
+      properties:
+        data:
+          $ref: "#/components/schemas/MfaToggleResponse"
+        error:
+          type: "null"
+        meta:
+          type: object
+          properties:
+            requestId:
+              type: string
+          additionalProperties: false
+      required:
+        - data
+        - error
+      additionalProperties: false
+    MfaToggleResponse:
+      type: object
+      properties:
+        enabled:
+          type: boolean
+      required:
+        - enabled
+      additionalProperties: false
+    MfaRecoveryRegenEnvelope:
+      type: object
+      properties:
+        data:
+          $ref: "#/components/schemas/MfaRecoveryCodesResponse"
+        error:
+          type: "null"
+        meta:
+          type: object
+          properties:
+            requestId:
+              type: string
+          additionalProperties: false
+      required:
+        - data
+        - error
+      additionalProperties: false
     PasskeyLoginVerifyResponse:
       type: object
       properties:
diff --git a/package.json b/package.json
index 29b6f8321..1474c7989 100644
--- a/package.json
+++ b/package.json
@@ -74,6 +74,7 @@
     "next": "16.2.9",
     "next-themes": "^0.4.6",
     "nodemailer": "^9.0.1",
+    "otpauth": "^9.5.1",
     "p-limit": "^7.3.0",
     "pg-boss": "^12.20.0",
     "prisma": "^7.8.0",
diff --git a/pnpm-lock.yaml b/pnpm-lock.yaml
index 525664542..8d9e539c5 100644
--- a/pnpm-lock.yaml
+++ b/pnpm-lock.yaml
@@ -84,6 +84,9 @@ importers:
       nodemailer:
         specifier: ^9.0.1
         version: 9.0.1
+      otpauth:
+        specifier: ^9.5.1
+        version: 9.5.1
       p-limit:
         specifier: ^7.3.0
         version: 7.3.0
@@ -1290,6 +1293,10 @@ packages:
     resolution: {integrity: sha512-jCs9ldd7NwzpgXDIf6P3+NrHh9/sD6CQdxHyjQI+h/6rDNo88ypBxxz45UDuZHz9r3tNz7N/VInSVoVdtXEI4A==}
     engines: {node: ^14.21.3 || >=16}
 
+  '@noble/hashes@2.2.0':
+    resolution: {integrity: sha512-IYqDGiTXab6FniAgnSdZwgWbomxpy9FtYvLKs7wCUs2a8RkITG+DFGO1DM9cr+E3/RgADRpFjrKVaJ1z6sjtEg==}
+    engines: {node: '>= 20.19.0'}
+
   '@nodable/entities@2.1.0':
     resolution: {integrity: sha512-nyT7T3nbMyBI/lvr6L5TyWbFJAI9FTgVRakNoBqCD+PmID8DzFrrNdLLtHMwMszOtqZa8PAOV24ZqDnQrhQINA==}
 
@@ -5396,6 +5403,9 @@ packages:
     resolution: {integrity: sha512-weP+BZ8MVNnlCm8c0Qdc1WSWq4Qn7I+9CJGm7Qali6g44e/PUzbjNqJX5NJ9ljlNMosfJvg1fKEGILklK9cwnw==}
     engines: {node: '>=18'}
 
+  otpauth@9.5.1:
+    resolution: {integrity: sha512-fJmDAHc8wImfqqqOXIlBvT1dEKrZK0Cmb2VEgScpNTolCz0PHh6ExUZGv4sLtOsWNaHCQlD+rRqaPgnoxFoZjQ==}
+
   outvariant@1.4.3:
     resolution: {integrity: sha512-+Sl2UErvtsoajRDKCE5/dBz4DIvHXQQnAxtQTF04OJxY0+DyZXSo5P5Bb7XYWOh81syohlYL24hbDwxedPUJCA==}
 
@@ -7978,6 +7988,8 @@ snapshots:
 
   '@noble/hashes@1.8.0': {}
 
+  '@noble/hashes@2.2.0': {}
+
   '@nodable/entities@2.1.0': {}
 
   '@node-rs/argon2-android-arm-eabi@2.0.2':
@@ -12157,6 +12169,10 @@ snapshots:
       string-width: 7.2.0
       strip-ansi: 7.2.0
 
+  otpauth@9.5.1:
+    dependencies:
+      '@noble/hashes': 2.2.0
+
   outvariant@1.4.3: {}
 
   own-keys@1.0.1:
diff --git a/prisma/migrations/0202_v123_totp_laststep/migration.sql b/prisma/migrations/0202_v123_totp_laststep/migration.sql
new file mode 100644
index 000000000..a4d5aa577
--- /dev/null
+++ b/prisma/migrations/0202_v123_totp_laststep/migration.sql
@@ -0,0 +1,11 @@
+-- v1.23 — TOTP replay guard.
+--
+-- Persists the last accepted time-step counter per account so a verified
+-- code cannot be replayed within its 30-second validity window. The verify
+-- path resolves the submitted code to its RFC 6238 step (`floor(now /
+-- period)` adjusted by the ±1 drift delta) and rejects any step that is not
+-- strictly greater than this column. Additive, nullable — existing rows
+-- (no TOTP enrolled) need no backfill, and a freshly confirmed factor starts
+-- with NULL (the first verify simply records its step).
+ALTER TABLE "users"
+  ADD COLUMN IF NOT EXISTS "totp_last_step" BIGINT;
diff --git a/prisma/schema.prisma b/prisma/schema.prisma
index 9aaf0ae5b..bf517cb88 100644
--- a/prisma/schema.prisma
+++ b/prisma/schema.prisma
@@ -556,6 +556,12 @@ model User {
   // `passkeyUpgradeNudgeDismissed` are per-account flags later waves read.
   totpSecretEncrypted          String?   @map("totp_secret_encrypted")
   totpConfirmedAt              DateTime? @map("totp_confirmed_at")
+  // v1.23 — TOTP replay guard. The last accepted time-step counter
+  // (RFC 6238 `T = floor(now / period)`). A code is rejected when its
+  // resolved step is <= this value even while still inside the ±1 drift
+  // window, so a captured code cannot be reused within its 30-second
+  // life. BigInt because the step counter grows unbounded with wall time.
+  totpLastStep                 BigInt?   @map("totp_last_step")
   mfaEnforced                  Boolean   @default(false) @map("mfa_enforced")
   passkeyUpgradeNudgeDismissed Boolean   @default(false) @map("passkey_upgrade_nudge_dismissed")
 
diff --git a/scripts/disable-mfa.ts b/scripts/disable-mfa.ts
new file mode 100644
index 000000000..456ccae76
--- /dev/null
+++ b/scripts/disable-mfa.ts
@@ -0,0 +1,90 @@
+/**
+ * scripts/disable-mfa.ts <email-or-username>
+ *
+ * Operator escape hatch: clear the second factor for an account whose owner
+ * has locked themselves out (lost authenticator AND recovery codes). Mirrors
+ * the password-reset CLI — it runs out-of-band against the database, so it is
+ * the recovery path of last resort for a self-hoster.
+ *
+ * It clears the TOTP secret, the confirmed-at stamp and the replay counter,
+ * and deletes every recovery code, then writes an `auth.mfa.disabled` audit
+ * row (with `details.source = "cli"`) so the action is traceable.
+ *
+ * Run via the bundled tsx (the production standalone image strips tsx):
+ *   pnpm dlx tsx scripts/disable-mfa.ts user@example.com
+ */
+import "dotenv/config";
+import { PrismaClient } from "@/generated/prisma/client";
+import { PrismaPg } from "@prisma/adapter-pg";
+
+const DATABASE_URL = process.env.DATABASE_URL;
+if (!DATABASE_URL) {
+  console.error("DATABASE_URL must be set");
+  process.exit(1);
+}
+
+const identifier = process.argv[2];
+if (!identifier) {
+  console.error(
+    "Usage: pnpm dlx tsx scripts/disable-mfa.ts <email-or-username>",
+  );
+  process.exit(2);
+}
+
+const prisma = new PrismaClient({
+  adapter: new PrismaPg({ connectionString: DATABASE_URL }),
+});
+
+async function main(): Promise<void> {
+  const user = await prisma.user.findFirst({
+    where: {
+      OR: [
+        { email: { equals: identifier, mode: "insensitive" } },
+        { username: { equals: identifier, mode: "insensitive" } },
+      ],
+    },
+    select: { id: true, username: true, totpConfirmedAt: true },
+  });
+
+  if (!user) {
+    console.error(`No account matches '${identifier}'.`);
+    process.exit(3);
+  }
+
+  if (!user.totpConfirmedAt) {
+    console.log(
+      `Account '${user.username}' has no active second factor — nothing to do.`,
+    );
+    return;
+  }
+
+  await prisma.$transaction(async (tx) => {
+    await tx.user.update({
+      where: { id: user.id },
+      data: {
+        totpSecretEncrypted: null,
+        totpConfirmedAt: null,
+        totpLastStep: null,
+      },
+    });
+    await tx.mfaRecoveryCode.deleteMany({ where: { userId: user.id } });
+    await tx.auditLog.create({
+      data: {
+        action: "auth.mfa.disabled",
+        userId: user.id,
+        details: JSON.stringify({ source: "cli", factor: "totp" }),
+      },
+    });
+  });
+
+  console.log(`Second factor cleared for account '${user.username}'.`);
+}
+
+main()
+  .catch((error) => {
+    console.error(error);
+    process.exit(1);
+  })
+  .finally(() => {
+    void prisma.$disconnect();
+  });
diff --git a/src/__tests__/api/auth/login/mfa-branch.test.ts b/src/__tests__/api/auth/login/mfa-branch.test.ts
new file mode 100644
index 000000000..e47fc51fd
--- /dev/null
+++ b/src/__tests__/api/auth/login/mfa-branch.test.ts
@@ -0,0 +1,131 @@
+import { describe, it, expect, vi, beforeEach } from "vitest";
+
+vi.mock("@/lib/db", () => ({
+  prisma: { user: { findFirst: vi.fn() } },
+}));
+vi.mock("@/lib/auth/password", () => ({
+  verifyPassword: vi.fn().mockResolvedValue(true),
+}));
+vi.mock("@/lib/auth/audit", () => ({
+  auditLog: vi.fn().mockResolvedValue(undefined),
+}));
+vi.mock("@/lib/auth/hmac", () => ({ hashToken: vi.fn(() => "h") }));
+vi.mock("@/lib/db-compat", () => ({
+  ensureDbCompatibility: vi.fn().mockResolvedValue(undefined),
+}));
+vi.mock("@/lib/logging/transports", () => ({ emitIfSampled: vi.fn() }));
+vi.mock("@/lib/rate-limit", () => ({
+  checkAuthSurfaceRateLimit: vi.fn().mockResolvedValue({
+    allowed: true,
+    remaining: 4,
+    resetAt: Date.now() + 1e6,
+    ip: "203.0.113.7",
+  }),
+  rateLimitHeaders: vi.fn(() => ({})),
+}));
+vi.mock("@/lib/auth/login-response", () => ({
+  finishLogin: vi.fn().mockResolvedValue(
+    new Response(
+      JSON.stringify({ data: { user: { id: "user-1" } }, error: null }),
+      {
+        status: 200,
+        headers: { "content-type": "application/json" },
+      },
+    ),
+  ),
+}));
+vi.mock("@/lib/auth/mfa/challenge", () => ({
+  createMfaChallenge: vi.fn().mockResolvedValue({
+    ticket: "opaque-ticket-value",
+    expiresAt: new Date(Date.now() + 5 * 60_000),
+  }),
+}));
+vi.mock("next/headers", () => ({
+  headers: vi.fn(async () => ({ get: () => null })),
+  cookies: vi.fn(async () => ({
+    get: () => undefined,
+    set: () => {},
+    delete: () => {},
+  })),
+}));
+
+import { POST } from "@/app/api/auth/login/route";
+import { prisma } from "@/lib/db";
+import { finishLogin } from "@/lib/auth/login-response";
+import { createMfaChallenge } from "@/lib/auth/mfa/challenge";
+
+function loginRequest() {
+  return new Request("http://localhost/api/auth/login", {
+    method: "POST",
+    headers: { "content-type": "application/json" },
+    body: JSON.stringify({
+      email: "user@example.com",
+      password: "correct-horse-battery",
+    }),
+  }) as unknown as Parameters<typeof POST>[0];
+}
+
+const BASE_USER = {
+  id: "user-1",
+  username: "u",
+  email: "user@example.com",
+  passwordHash: "argon2-hash",
+  onboardingCompletedAt: new Date(),
+};
+
+beforeEach(() => {
+  vi.clearAllMocks();
+});
+
+describe("login MFA branch", () => {
+  it("MFA user → returns mfaRequired + ticket and issues NO session", async () => {
+    vi.mocked(prisma.user.findFirst).mockResolvedValue({
+      ...BASE_USER,
+      totpConfirmedAt: new Date(),
+    } as never);
+
+    const res = await POST(loginRequest());
+    expect(res.status).toBe(200);
+    const body = await res.json();
+
+    expect(body.data).toBeNull();
+    expect(body.error).toBeNull();
+    expect(body.meta.mfaRequired).toBe(true);
+    expect(body.meta.mfaTicket).toBe("opaque-ticket-value");
+    expect(body.meta.methods).toEqual(["totp", "recovery"]);
+
+    expect(createMfaChallenge).toHaveBeenCalledWith("user-1", "login");
+    // The session/token tail is never reached.
+    expect(finishLogin).not.toHaveBeenCalled();
+  });
+
+  it("non-MFA user → issues the session via finishLogin, no challenge", async () => {
+    vi.mocked(prisma.user.findFirst).mockResolvedValue({
+      ...BASE_USER,
+      totpConfirmedAt: null,
+    } as never);
+
+    const res = await POST(loginRequest());
+    expect(res.status).toBe(200);
+
+    expect(finishLogin).toHaveBeenCalledTimes(1);
+    expect(createMfaChallenge).not.toHaveBeenCalled();
+    const arg = vi.mocked(finishLogin).mock.calls[0][0];
+    expect(arg.source).toBe("login.password");
+    expect(arg.mfaVerified).toBeUndefined();
+  });
+
+  it("wrong password never reaches the MFA branch", async () => {
+    const { verifyPassword } = await import("@/lib/auth/password");
+    vi.mocked(verifyPassword).mockResolvedValueOnce(false);
+    vi.mocked(prisma.user.findFirst).mockResolvedValue({
+      ...BASE_USER,
+      totpConfirmedAt: new Date(),
+    } as never);
+
+    const res = await POST(loginRequest());
+    expect(res.status).toBe(401);
+    expect(createMfaChallenge).not.toHaveBeenCalled();
+    expect(finishLogin).not.toHaveBeenCalled();
+  });
+});
diff --git a/src/__tests__/api/auth/mfa/verify.test.ts b/src/__tests__/api/auth/mfa/verify.test.ts
new file mode 100644
index 000000000..b16904be3
--- /dev/null
+++ b/src/__tests__/api/auth/mfa/verify.test.ts
@@ -0,0 +1,156 @@
+import { describe, it, expect, vi, beforeEach } from "vitest";
+
+vi.mock("@/lib/db", () => ({
+  prisma: { user: { findUnique: vi.fn() } },
+}));
+vi.mock("@/lib/db-compat", () => ({
+  ensureDbCompatibility: vi.fn().mockResolvedValue(undefined),
+}));
+vi.mock("@/lib/logging/transports", () => ({ emitIfSampled: vi.fn() }));
+vi.mock("@/lib/auth/audit", () => ({
+  auditLog: vi.fn().mockResolvedValue(undefined),
+}));
+vi.mock("@/lib/rate-limit", () => ({
+  checkAuthSurfaceRateLimit: vi.fn().mockResolvedValue({
+    allowed: true,
+    remaining: 9,
+    resetAt: Date.now() + 1e6,
+    ip: "203.0.113.9",
+  }),
+  rateLimitHeaders: vi.fn(() => ({})),
+}));
+vi.mock("@/lib/auth/login-response", () => ({
+  finishLogin: vi
+    .fn()
+    .mockResolvedValue(
+      new Response(
+        JSON.stringify({ data: { user: { id: "user-1" } }, error: null }),
+        { status: 200, headers: { "content-type": "application/json" } },
+      ),
+    ),
+}));
+vi.mock("@/lib/auth/mfa/challenge", () => ({
+  loadActiveChallenge: vi.fn(),
+  recordChallengeFailure: vi
+    .fn()
+    .mockResolvedValue({ exhausted: false, attempts: 1 }),
+  claimChallenge: vi.fn(),
+}));
+vi.mock("@/lib/auth/mfa/verify-factor", () => ({
+  verifyMfaFactor: vi.fn(),
+}));
+vi.mock("next/headers", () => ({
+  headers: vi.fn(async () => ({ get: () => null })),
+  cookies: vi.fn(async () => ({
+    get: () => undefined,
+    set: () => {},
+    delete: () => {},
+  })),
+}));
+
+import { POST } from "@/app/api/auth/mfa/verify/route";
+import { prisma } from "@/lib/db";
+import { finishLogin } from "@/lib/auth/login-response";
+import {
+  loadActiveChallenge,
+  recordChallengeFailure,
+  claimChallenge,
+} from "@/lib/auth/mfa/challenge";
+import { verifyMfaFactor } from "@/lib/auth/mfa/verify-factor";
+
+function verifyRequest(body: unknown) {
+  return new Request("http://localhost/api/auth/mfa/verify", {
+    method: "POST",
+    headers: { "content-type": "application/json" },
+    body: JSON.stringify(body),
+  }) as unknown as Parameters<typeof POST>[0];
+}
+
+const GOOD_BODY = { mfaTicket: "tkt", method: "totp", code: "123456" };
+const ACTIVE_CHALLENGE = {
+  id: "ch-1",
+  userId: "user-1",
+  kind: "login",
+  attempts: 0,
+  expiresAt: new Date(Date.now() + 60_000),
+};
+const MFA_USER = {
+  id: "user-1",
+  username: "u",
+  email: "user@example.com",
+  onboardingCompletedAt: new Date(),
+  totpConfirmedAt: new Date(),
+  totpSecretEncrypted: "v2.cipher",
+  totpLastStep: null,
+};
+
+beforeEach(() => {
+  vi.clearAllMocks();
+});
+
+describe("POST /api/auth/mfa/verify", () => {
+  it("happy path: valid factor → claims ticket and issues the bundle", async () => {
+    vi.mocked(loadActiveChallenge).mockResolvedValue(ACTIVE_CHALLENGE as never);
+    vi.mocked(prisma.user.findUnique).mockResolvedValue(MFA_USER as never);
+    vi.mocked(verifyMfaFactor).mockResolvedValue({ ok: true, replay: false });
+    vi.mocked(claimChallenge).mockResolvedValue(true);
+
+    const res = await POST(verifyRequest(GOOD_BODY));
+    expect(res.status).toBe(200);
+
+    expect(claimChallenge).toHaveBeenCalledWith("ch-1");
+    expect(finishLogin).toHaveBeenCalledTimes(1);
+    const arg = vi.mocked(finishLogin).mock.calls[0][0];
+    expect(arg.mfaVerified).toBe(true);
+    expect(arg.source).toBe("mfa.verify");
+  });
+
+  it("invalid ticket → 401, no session", async () => {
+    vi.mocked(loadActiveChallenge).mockResolvedValue(null);
+    const res = await POST(verifyRequest(GOOD_BODY));
+    expect(res.status).toBe(401);
+    expect(finishLogin).not.toHaveBeenCalled();
+  });
+
+  it("wrong code → records failure, 401, no session", async () => {
+    vi.mocked(loadActiveChallenge).mockResolvedValue(ACTIVE_CHALLENGE as never);
+    vi.mocked(prisma.user.findUnique).mockResolvedValue(MFA_USER as never);
+    vi.mocked(verifyMfaFactor).mockResolvedValue({ ok: false, replay: false });
+
+    const res = await POST(verifyRequest(GOOD_BODY));
+    expect(res.status).toBe(401);
+    expect(recordChallengeFailure).toHaveBeenCalledWith("ch-1");
+    expect(claimChallenge).not.toHaveBeenCalled();
+    expect(finishLogin).not.toHaveBeenCalled();
+  });
+
+  it("factor valid but claim lost (race) → 401, no session", async () => {
+    vi.mocked(loadActiveChallenge).mockResolvedValue(ACTIVE_CHALLENGE as never);
+    vi.mocked(prisma.user.findUnique).mockResolvedValue(MFA_USER as never);
+    vi.mocked(verifyMfaFactor).mockResolvedValue({ ok: true, replay: false });
+    vi.mocked(claimChallenge).mockResolvedValue(false);
+
+    const res = await POST(verifyRequest(GOOD_BODY));
+    expect(res.status).toBe(401);
+    expect(finishLogin).not.toHaveBeenCalled();
+  });
+
+  it("factor disabled between password and verify → failure, 401", async () => {
+    vi.mocked(loadActiveChallenge).mockResolvedValue(ACTIVE_CHALLENGE as never);
+    vi.mocked(prisma.user.findUnique).mockResolvedValue({
+      ...MFA_USER,
+      totpConfirmedAt: null,
+    } as never);
+
+    const res = await POST(verifyRequest(GOOD_BODY));
+    expect(res.status).toBe(401);
+    expect(recordChallengeFailure).toHaveBeenCalledWith("ch-1");
+    expect(verifyMfaFactor).not.toHaveBeenCalled();
+    expect(finishLogin).not.toHaveBeenCalled();
+  });
+
+  it("malformed body → 422", async () => {
+    const res = await POST(verifyRequest({ mfaTicket: "", code: "x" }));
+    expect(res.status).toBe(422);
+  });
+});
diff --git a/src/app/api/auth/login/route.ts b/src/app/api/auth/login/route.ts
index c4e727ee0..d271cfd31 100644
--- a/src/app/api/auth/login/route.ts
+++ b/src/app/api/auth/login/route.ts
@@ -1,22 +1,16 @@
 import { prisma } from "@/lib/db";
 import { loginPasswordSchema } from "@/lib/validations/auth";
 import { verifyPassword } from "@/lib/auth/password";
-import { createSession } from "@/lib/auth/session";
 import { auditLog } from "@/lib/auth/audit";
 import { hashToken } from "@/lib/auth/hmac";
-import { apiSuccess, apiError, safeJson } from "@/lib/api-response";
+import { apiError, safeJson } from "@/lib/api-response";
 import { checkAuthSurfaceRateLimit, rateLimitHeaders } from "@/lib/rate-limit";
 import { ensureDbCompatibility } from "@/lib/db-compat";
 import { NextRequest, NextResponse } from "next/server";
 import { apiHandler } from "@/lib/api-handler";
 import { annotate } from "@/lib/logging/context";
-import { issueApiToken, isNativeClientRequest } from "@/lib/auth/issue-token";
-import {
-  resolveTokenPolicy,
-  shouldIssueBearerToken,
-  isCookielessNativeCaller,
-} from "@/lib/auth/native-client";
-import { issueAccessAndRefresh } from "@/lib/auth/refresh-token";
+import { finishLogin } from "@/lib/auth/login-response";
+import { createMfaChallenge } from "@/lib/auth/mfa/challenge";
 
 export const POST = apiHandler(async (request: NextRequest) => {
   // v1.4.43 W13 M-4 — `checkAuthSurfaceRateLimit` swaps to a tighter
@@ -95,93 +89,55 @@ export const POST = apiHandler(async (request: NextRequest) => {
   }
 
   const ua = request.headers.get("user-agent");
-  // v1.4.22 W5 reconcile (Sr-H1) — `createSession` now anchors the
-  // `hl_onboarding` cookie itself; pass the user's onboarding state
-  // through so the proxy can short-circuit the redirect before the
-  // page hydrates.
-  await createSession(user.id, user.onboardingCompletedAt == null, ip, ua);
 
   await auditLog("auth.login.password", {
     userId: user.id,
     ipAddress: ip,
   });
 
-  annotate({ action: { name: "auth.login.password" } });
-
-  // v1.4 G4: Native callers (iOS, n8n, Health-Connect, unrecognised UAs)
-  // get a 24h access token + 60d rotating refresh token. Web UAs keep the
-  // legacy 90d Bearer (issued only when X-Client-Type: native is set —
-  // browser flows continue to use the session cookie).
-  if (
-    shouldIssueBearerToken(request.headers) ||
-    isNativeClientRequest(request.headers)
-  ) {
-    const policy = resolveTokenPolicy(request.headers);
-    const deviceId = request.headers.get("x-device-id");
-
-    // M-3 hardening: a 60-day refresh token is only ever delivered to a
-    // genuinely cookie-less native caller. A browser spoofing
-    // `X-Client-Type: native` (Mozilla UA or an inbound session cookie)
-    // falls through to the plain access-token path below — never handed a
-    // long-lived secret into a DOM/XSS-reachable context.
-    if (
-      policy.refreshTokenDays !== null &&
-      isCookielessNativeCaller(request.headers)
-    ) {
-      const bundle = await issueAccessAndRefresh({
-        userId: user.id,
-        policy,
-        deviceId,
-        userAgent: ua,
-        ipAddress: ip,
-        source: "login.password",
-      });
-      await auditLog("auth.token.autoissue.native", {
-        userId: user.id,
-        ipAddress: ip,
-        details: { source: "login.password", policy: "native" },
-      });
-      annotate({
-        action: { name: "auth.token.autoissue.native" },
-        meta: { token_policy: "native" },
-      });
-      return apiSuccess({
-        user: { id: user.id, username: user.username },
-        token: bundle.accessToken,
-        tokenExpiresAt: bundle.accessTokenExpiresAt.toISOString(),
-        refreshToken: bundle.refreshToken,
-        refreshTokenExpiresAt: bundle.refreshTokenExpiresAt.toISOString(),
-      });
-    }
-
-    // Web policy with explicit X-Client-Type:native (legacy iOS auto-login)
-    const issued = await issueApiToken({
-      userId: user.id,
-      name: `web auto-login ${new Date().toISOString()}`,
-      permissions: ["*"],
-      expiresInDays: policy.accessTokenDays,
-    });
-    await auditLog("auth.token.autoissue.native", {
+  // v1.23 — second-factor gate. The password is correct, but an account with
+  // a confirmed TOTP factor is NOT yet authenticated: no `Session` row and no
+  // token bundle is minted here. Instead a single-use, ~5-minute MFA ticket is
+  // returned (the partial state lives in the ticket, never in a half-built
+  // session) and the client completes the login at `/api/auth/mfa/verify`.
+  //
+  // Enumeration note: `meta.mfaRequired` is only ever returned AFTER a valid
+  // password, and the invalid-credentials response above is identical
+  // regardless of MFA state — an attacker without the password cannot learn
+  // whether an account has MFA.
+  if (user.totpConfirmedAt) {
+    const challenge = await createMfaChallenge(user.id, "login");
+    await auditLog("auth.mfa.challenge", {
       userId: user.id,
       ipAddress: ip,
-      details: {
-        tokenId: issued.tokenId,
-        source: "login.password",
-        policy: "web",
-      },
+      details: { source: "login.password" },
     });
     annotate({
-      action: { name: "auth.token.autoissue.native" },
-      meta: { token_policy: "web" },
-    });
-    return apiSuccess({
-      user: { id: user.id, username: user.username },
-      token: issued.token,
-      tokenExpiresAt: issued.expiresAt.toISOString(),
+      action: { name: "auth.mfa.challenge" },
+      meta: { mfa_required: true },
     });
+    return NextResponse.json(
+      {
+        data: null,
+        error: null,
+        meta: {
+          mfaRequired: true,
+          mfaTicket: challenge.ticket,
+          methods: ["totp", "recovery"],
+        },
+      },
+      { status: 200 },
+    );
   }
 
-  return apiSuccess({
-    user: { id: user.id, username: user.username },
+  annotate({ action: { name: "auth.login.password" } });
+
+  // No second factor — issue the session/token exactly as before.
+  return finishLogin({
+    user,
+    request,
+    ip,
+    userAgent: ua,
+    source: "login.password",
   });
 });
diff --git a/src/app/api/auth/me/mfa/disable/route.ts b/src/app/api/auth/me/mfa/disable/route.ts
new file mode 100644
index 000000000..24a266288
--- /dev/null
+++ b/src/app/api/auth/me/mfa/disable/route.ts
@@ -0,0 +1,100 @@
+/**
+ * POST /api/auth/me/mfa/disable
+ *
+ * Tear down the second factor. Double-gated:
+ *  1. `requireFreshMfa` — a cookie session that completed a second factor
+ *     within the step-up window (Bearer can never satisfy this).
+ *  2. A current TOTP or recovery code in the body — proves live possession at
+ *     the moment of the destructive action, not just a stale fresh-session.
+ *
+ * On success it clears `totpSecretEncrypted` / `totpConfirmedAt` /
+ * `totpLastStep` and deletes every recovery code in one transaction.
+ */
+import {
+  apiHandler,
+  requireFreshMfa,
+  HttpError,
+  MFA_STEP_UP_MAX_AGE_SECONDS,
+} from "@/lib/api-handler";
+import { apiError, apiSuccess, getClientIp } from "@/lib/api-response";
+import { annotate } from "@/lib/logging/context";
+import { auditLog } from "@/lib/auth/audit";
+import { prisma } from "@/lib/db";
+import { checkRateLimit, rateLimitHeaders } from "@/lib/rate-limit";
+import { verifyMfaFactor } from "@/lib/auth/mfa/verify-factor";
+import { mfaDisableSchema } from "@/lib/validations/mfa";
+
+export const dynamic = "force-dynamic";
+
+const DISABLE_RATE_LIMIT = 5;
+const DISABLE_WINDOW_MS = 15 * 60 * 1000;
+
+export const POST = apiHandler(async (req: Request) => {
+  // Step-up gate first — throws StepUpRequiredError (401 + errorCode) if the
+  // session is not freshly second-factor-verified.
+  const { user } = await requireFreshMfa(MFA_STEP_UP_MAX_AGE_SECONDS);
+
+  const rl = await checkRateLimit(
+    `mfa:disable:${user.id}`,
+    DISABLE_RATE_LIMIT,
+    DISABLE_WINDOW_MS,
+  );
+  if (!rl.allowed) {
+    const res = apiError("Too many requests", 429);
+    for (const [k, v] of Object.entries(rateLimitHeaders(rl))) {
+      res.headers.set(k, v);
+    }
+    return res;
+  }
+
+  let body: unknown;
+  try {
+    body = await req.json();
+  } catch {
+    throw new HttpError(400, "Invalid JSON body");
+  }
+  const parsed = mfaDisableSchema.safeParse(body);
+  if (!parsed.success) {
+    return apiError("Invalid request", 422);
+  }
+
+  const factor = await verifyMfaFactor(
+    user,
+    parsed.data.method,
+    parsed.data.code,
+  );
+  if (!factor.ok) {
+    await auditLog("auth.mfa.failed", {
+      userId: user.id,
+      ipAddress: getClientIp(req),
+      details: {
+        stage: "disable",
+        method: parsed.data.method,
+        replay: factor.replay,
+      },
+    });
+    annotate({ action: { name: "auth.mfa.disable.invalid_factor" } });
+    throw new HttpError(401, "Invalid code");
+  }
+
+  await prisma.$transaction(async (tx) => {
+    await tx.user.update({
+      where: { id: user.id },
+      data: {
+        totpSecretEncrypted: null,
+        totpConfirmedAt: null,
+        totpLastStep: null,
+      },
+    });
+    await tx.mfaRecoveryCode.deleteMany({ where: { userId: user.id } });
+  });
+
+  await auditLog("auth.mfa.disabled", {
+    userId: user.id,
+    ipAddress: getClientIp(req),
+    details: { factor: parsed.data.method },
+  });
+  annotate({ action: { name: "auth.mfa.disabled" } });
+
+  return apiSuccess({ enabled: false });
+});
diff --git a/src/app/api/auth/me/mfa/recovery-codes/regenerate/route.ts b/src/app/api/auth/me/mfa/recovery-codes/regenerate/route.ts
new file mode 100644
index 000000000..a82e3d87d
--- /dev/null
+++ b/src/app/api/auth/me/mfa/recovery-codes/regenerate/route.ts
@@ -0,0 +1,60 @@
+/**
+ * POST /api/auth/me/mfa/recovery-codes/regenerate
+ *
+ * Issue a fresh recovery-code batch, invalidating the entire prior set in one
+ * transaction. Step-up gated (`requireFreshMfa`) — a recovery-code rotation is
+ * a sensitive action; Bearer can never satisfy the gate. The new codes are
+ * returned **once**.
+ */
+import {
+  apiHandler,
+  requireFreshMfa,
+  HttpError,
+  MFA_STEP_UP_MAX_AGE_SECONDS,
+} from "@/lib/api-handler";
+import { apiError, apiSuccess, getClientIp } from "@/lib/api-response";
+import { annotate } from "@/lib/logging/context";
+import { auditLog } from "@/lib/auth/audit";
+import { checkRateLimit, rateLimitHeaders } from "@/lib/rate-limit";
+import { regenerateRecoveryCodes } from "@/lib/auth/mfa/recovery-codes";
+
+export const dynamic = "force-dynamic";
+
+const REGEN_RATE_LIMIT = 5;
+const REGEN_WINDOW_MS = 15 * 60 * 1000;
+
+export const POST = apiHandler(async (req: Request) => {
+  const { user } = await requireFreshMfa(MFA_STEP_UP_MAX_AGE_SECONDS);
+
+  // Defence in depth — regeneration only makes sense for an active factor.
+  if (!user.totpConfirmedAt) {
+    throw new HttpError(409, "No second factor is active");
+  }
+
+  const rl = await checkRateLimit(
+    `mfa:recovery-regen:${user.id}`,
+    REGEN_RATE_LIMIT,
+    REGEN_WINDOW_MS,
+  );
+  if (!rl.allowed) {
+    const res = apiError("Too many requests", 429);
+    for (const [k, v] of Object.entries(rateLimitHeaders(rl))) {
+      res.headers.set(k, v);
+    }
+    return res;
+  }
+
+  const recoveryCodes = await regenerateRecoveryCodes(user.id);
+
+  await auditLog("auth.mfa.recovery_regenerated", {
+    userId: user.id,
+    ipAddress: getClientIp(req),
+    details: { count: recoveryCodes.length },
+  });
+  annotate({ action: { name: "auth.mfa.recovery_regenerated" } });
+
+  return apiSuccess({
+    recoveryCodes,
+    recoveryCodesRemaining: recoveryCodes.length,
+  });
+});
diff --git a/src/app/api/auth/me/mfa/totp/confirm/route.ts b/src/app/api/auth/me/mfa/totp/confirm/route.ts
new file mode 100644
index 000000000..861c7c7a3
--- /dev/null
+++ b/src/app/api/auth/me/mfa/totp/confirm/route.ts
@@ -0,0 +1,124 @@
+/**
+ * POST /api/auth/me/mfa/totp/confirm
+ *
+ * Finish TOTP enrollment. Verifies a code against the pending secret; on
+ * success it promotes pending → active (`totpConfirmedAt = now()`), records
+ * the accepted time-step (replay guard), generates + persists the Argon2id-
+ * hashed recovery codes, and returns the codes **once** for the user to save.
+ *
+ * The completing session is also stamped `mfaVerifiedAt = now()` so the user
+ * can immediately manage the freshly-enabled factor (disable / regenerate
+ * codes) without an extra step-up round-trip.
+ *
+ * Cookie-only (`requireCookieAuth`): an API token can never enrol MFA.
+ */
+import { apiHandler, requireCookieAuth, HttpError } from "@/lib/api-handler";
+import { apiError, apiSuccess, getClientIp } from "@/lib/api-response";
+import { annotate } from "@/lib/logging/context";
+import { auditLog } from "@/lib/auth/audit";
+import { prisma } from "@/lib/db";
+import { decrypt } from "@/lib/crypto";
+import { checkRateLimit, rateLimitHeaders } from "@/lib/rate-limit";
+import { verifyTotp } from "@/lib/auth/mfa/totp";
+import {
+  generateRecoveryCodes,
+  persistRecoveryCodes,
+} from "@/lib/auth/mfa/recovery-codes";
+import { totpConfirmSchema } from "@/lib/validations/mfa";
+
+export const dynamic = "force-dynamic";
+
+const CONFIRM_RATE_LIMIT = 10;
+const CONFIRM_WINDOW_MS = 15 * 60 * 1000;
+
+export const POST = apiHandler(async (req: Request) => {
+  const { user, session } = await requireCookieAuth();
+
+  const rl = await checkRateLimit(
+    `mfa:confirm:${user.id}`,
+    CONFIRM_RATE_LIMIT,
+    CONFIRM_WINDOW_MS,
+  );
+  if (!rl.allowed) {
+    const res = apiError("Too many requests", 429);
+    for (const [k, v] of Object.entries(rateLimitHeaders(rl))) {
+      res.headers.set(k, v);
+    }
+    return res;
+  }
+
+  if (user.totpConfirmedAt) {
+    throw new HttpError(409, "A second factor is already active");
+  }
+  if (!user.totpSecretEncrypted) {
+    throw new HttpError(409, "Start enrollment before confirming");
+  }
+
+  let body: unknown;
+  try {
+    body = await req.json();
+  } catch {
+    throw new HttpError(400, "Invalid JSON body");
+  }
+  const parsed = totpConfirmSchema.safeParse(body);
+  if (!parsed.success) {
+    return apiError("Invalid code", 422);
+  }
+
+  // Decrypt is fail-closed — a missing/rotated key throws rather than
+  // confirming against junk.
+  const secret = decrypt(user.totpSecretEncrypted);
+  const result = verifyTotp(
+    secret,
+    parsed.data.code,
+    user.totpLastStep === null ? null : Number(user.totpLastStep),
+  );
+
+  if (!result.valid) {
+    await auditLog("auth.mfa.failed", {
+      userId: user.id,
+      ipAddress: getClientIp(req),
+      details: { stage: "confirm", replay: result.replay },
+    });
+    annotate({
+      action: { name: "auth.mfa.totp.confirm.invalid" },
+      meta: { replay: result.replay },
+    });
+    throw new HttpError(401, "Invalid code");
+  }
+
+  const recoveryCodes = generateRecoveryCodes();
+
+  await prisma.$transaction(async (tx) => {
+    await tx.user.update({
+      where: { id: user.id },
+      data: {
+        totpConfirmedAt: new Date(),
+        totpLastStep: BigInt(result.step as number),
+      },
+    });
+    // A fresh enrollment starts from a clean recovery set.
+    await tx.mfaRecoveryCode.deleteMany({ where: { userId: user.id } });
+    await persistRecoveryCodes(tx, user.id, recoveryCodes);
+    // Stamp the completing session so the user can immediately manage the
+    // factor under step-up without re-verifying.
+    await tx.session.updateMany({
+      where: { id: session.id },
+      data: { mfaVerifiedAt: new Date() },
+    });
+  });
+
+  await auditLog("auth.mfa.enabled", {
+    userId: user.id,
+    ipAddress: getClientIp(req),
+    details: { factor: "totp" },
+  });
+  annotate({ action: { name: "auth.mfa.enabled" } });
+
+  // `recoveryCodes` is redaction-denylisted (`/recovery.?code/i`).
+  return apiSuccess({
+    enabled: true,
+    recoveryCodes,
+    recoveryCodesRemaining: recoveryCodes.length,
+  });
+});
diff --git a/src/app/api/auth/me/mfa/totp/setup/route.ts b/src/app/api/auth/me/mfa/totp/setup/route.ts
new file mode 100644
index 000000000..57fa885d5
--- /dev/null
+++ b/src/app/api/auth/me/mfa/totp/setup/route.ts
@@ -0,0 +1,76 @@
+/**
+ * POST /api/auth/me/mfa/totp/setup
+ *
+ * Begin TOTP enrollment. Generates a 160-bit secret, stores it **encrypted**
+ * (AES-256-GCM, the same at-rest envelope as every other credential), and
+ * returns the `otpauth://` URI + the raw Base32 secret so the client can
+ * render the QR and offer manual entry. The secret is **pending** — MFA is
+ * not active until `/confirm` verifies a code, so `totpConfirmedAt` stays
+ * null here.
+ *
+ * Cookie-only (`requireCookieAuth`): an API token can never enrol MFA. The
+ * recovery-code batch is issued at `/confirm` (after the factor is proven),
+ * not here, so an abandoned setup never persists codes.
+ */
+import { apiHandler, requireCookieAuth, HttpError } from "@/lib/api-handler";
+import { apiError, apiSuccess, getClientIp } from "@/lib/api-response";
+import { annotate } from "@/lib/logging/context";
+import { auditLog } from "@/lib/auth/audit";
+import { prisma } from "@/lib/db";
+import { encrypt } from "@/lib/crypto";
+import { checkRateLimit, rateLimitHeaders } from "@/lib/rate-limit";
+import { generateTotpSecret, buildOtpauthUri } from "@/lib/auth/mfa/totp";
+
+export const dynamic = "force-dynamic";
+
+const SETUP_RATE_LIMIT = 5;
+const SETUP_WINDOW_MS = 15 * 60 * 1000;
+
+export const POST = apiHandler(async (req: Request) => {
+  const { user } = await requireCookieAuth();
+
+  const rl = await checkRateLimit(
+    `mfa:setup:${user.id}`,
+    SETUP_RATE_LIMIT,
+    SETUP_WINDOW_MS,
+  );
+  if (!rl.allowed) {
+    const res = apiError("Too many requests", 429);
+    for (const [k, v] of Object.entries(rateLimitHeaders(rl))) {
+      res.headers.set(k, v);
+    }
+    return res;
+  }
+
+  // An already-active factor must be disabled (step-up gated) before a new
+  // secret can be enrolled — re-running setup must not silently rotate the
+  // live secret out from under the user's authenticator.
+  if (user.totpConfirmedAt) {
+    annotate({ action: { name: "auth.mfa.totp.setup.already_active" } });
+    throw new HttpError(409, "A second factor is already active");
+  }
+
+  const secret = generateTotpSecret();
+  const account = user.email ?? user.username;
+  const otpauthUri = buildOtpauthUri(secret, account);
+
+  // Store the pending secret encrypted; leave `totpConfirmedAt` null.
+  await prisma.user.update({
+    where: { id: user.id },
+    data: {
+      totpSecretEncrypted: encrypt(secret),
+      // A re-setup resets the replay counter — the new secret starts fresh.
+      totpLastStep: null,
+    },
+  });
+
+  await auditLog("auth.mfa.totp.setup", {
+    userId: user.id,
+    ipAddress: getClientIp(req),
+  });
+  annotate({ action: { name: "auth.mfa.totp.setup" } });
+
+  // `totpSecret` / `otpauthUri` are redaction-denylisted (`/totp/i`,
+  // `/otp/i`, `/secret/i`) so they never surface in a wide-event excerpt.
+  return apiSuccess({ otpauthUri, totpSecret: secret });
+});
diff --git a/src/app/api/auth/mfa/verify/route.ts b/src/app/api/auth/mfa/verify/route.ts
new file mode 100644
index 000000000..adf7dfde8
--- /dev/null
+++ b/src/app/api/auth/mfa/verify/route.ts
@@ -0,0 +1,139 @@
+/**
+ * POST /api/auth/mfa/verify
+ *
+ * Complete a second-factor login challenge. The caller presents the opaque
+ * `mfaTicket` from the `meta.mfaRequired` login response plus a TOTP or
+ * recovery code. On success the **same** session/token bundle the password
+ * path issues is returned (web → session cookie; native → access+refresh),
+ * with the session stamped `mfaVerifiedAt`.
+ *
+ * Security-critical invariants:
+ * - No session or token exists until the factor passes — the partial state
+ *   lived in the ticket, never in a half-built session.
+ * - The ticket is **claimed once, atomically**, only AFTER the factor
+ *   verifies; two concurrent valid submissions can mint at most one session.
+ * - Wrong factors increment the ticket attempt counter and burn it at the
+ *   cap (NIST throttle, not an account lock). Anonymous surface is rate-
+ *   limited per IP on top of the per-ticket cap.
+ */
+import { NextRequest } from "next/server";
+import { apiError, safeJson } from "@/lib/api-response";
+import { apiHandler } from "@/lib/api-handler";
+import { annotate } from "@/lib/logging/context";
+import { auditLog } from "@/lib/auth/audit";
+import { prisma } from "@/lib/db";
+import { ensureDbCompatibility } from "@/lib/db-compat";
+import { checkAuthSurfaceRateLimit, rateLimitHeaders } from "@/lib/rate-limit";
+import { finishLogin } from "@/lib/auth/login-response";
+import {
+  loadActiveChallenge,
+  recordChallengeFailure,
+  claimChallenge,
+} from "@/lib/auth/mfa/challenge";
+import { verifyMfaFactor } from "@/lib/auth/mfa/verify-factor";
+import { mfaVerifySchema } from "@/lib/validations/mfa";
+
+export const dynamic = "force-dynamic";
+
+export const POST = apiHandler(async (request: NextRequest) => {
+  const rl = await checkAuthSurfaceRateLimit(
+    request,
+    "auth:mfa-verify",
+    10,
+    15 * 60 * 1000,
+  );
+  const ip = rl.ip ?? "unknown";
+  if (!rl.allowed) {
+    return apiError("Too many attempts. Please try again later.", 429, {
+      headers: rateLimitHeaders(rl),
+    });
+  }
+
+  await ensureDbCompatibility();
+
+  const { data: body, error: jsonError } = await safeJson(request, {
+    maxBytes: 16 * 1024,
+  });
+  if (jsonError) return jsonError;
+
+  const parsed = mfaVerifySchema.safeParse(body);
+  if (!parsed.success) {
+    return apiError("Invalid request", 422);
+  }
+  const { mfaTicket, method, code } = parsed.data;
+
+  // Resolve the ticket. A single generic 401 covers unknown / expired /
+  // consumed / over-cap so a ticket-guesser learns nothing.
+  const challenge = await loadActiveChallenge(mfaTicket);
+  if (!challenge) {
+    annotate({ action: { name: "auth.mfa.verify.invalid_ticket" } });
+    return apiError("Invalid or expired challenge", 401);
+  }
+
+  const user = await prisma.user.findUnique({
+    where: { id: challenge.userId },
+    select: {
+      id: true,
+      username: true,
+      email: true,
+      onboardingCompletedAt: true,
+      totpConfirmedAt: true,
+      totpSecretEncrypted: true,
+      totpLastStep: true,
+    },
+  });
+
+  // The factor must still be active (it could have been disabled between the
+  // password step and this call). Treat anything else as a failed attempt.
+  if (!user || !user.totpConfirmedAt) {
+    await recordChallengeFailure(challenge.id);
+    annotate({ action: { name: "auth.mfa.verify.no_active_factor" } });
+    return apiError("Invalid or expired challenge", 401);
+  }
+
+  const factor = await verifyMfaFactor(user, method, code);
+  if (!factor.ok) {
+    const { exhausted } = await recordChallengeFailure(challenge.id);
+    await auditLog("auth.mfa.failed", {
+      userId: user.id,
+      ipAddress: ip,
+      details: { stage: "login", method, replay: factor.replay, exhausted },
+    });
+    annotate({
+      action: { name: "auth.mfa.failed" },
+      meta: { method, replay: factor.replay, exhausted },
+    });
+    return apiError("Invalid code", 401);
+  }
+
+  // Factor verified — claim the ticket atomically. Only the single winning
+  // caller proceeds to mint a session; a concurrent claim loses here.
+  const claimed = await claimChallenge(challenge.id);
+  if (!claimed) {
+    annotate({ action: { name: "auth.mfa.verify.claim_lost" } });
+    return apiError("Invalid or expired challenge", 401);
+  }
+
+  await auditLog("auth.mfa.verified", {
+    userId: user.id,
+    ipAddress: ip,
+    details: { method },
+  });
+  if (method === "recovery") {
+    await auditLog("auth.mfa.recovery_used", {
+      userId: user.id,
+      ipAddress: ip,
+    });
+  }
+  annotate({ action: { name: "auth.mfa.verified" }, meta: { method } });
+
+  const ua = request.headers.get("user-agent");
+  return finishLogin({
+    user,
+    request,
+    ip,
+    userAgent: ua,
+    source: "mfa.verify",
+    mfaVerified: true,
+  });
+});
diff --git a/src/lib/__tests__/require-fresh-mfa.test.ts b/src/lib/__tests__/require-fresh-mfa.test.ts
new file mode 100644
index 000000000..8093ab688
--- /dev/null
+++ b/src/lib/__tests__/require-fresh-mfa.test.ts
@@ -0,0 +1,113 @@
+import { describe, it, expect, vi, beforeEach } from "vitest";
+
+// Mirrors require-auth-bearer.test.ts mocking so the api-handler module loads
+// without a live DB / request scope.
+vi.mock("@/lib/db", () => ({
+  prisma: {
+    session: { findUnique: vi.fn() },
+  },
+}));
+
+vi.mock("@/lib/auth/session", () => ({
+  getSession: vi.fn(),
+}));
+
+vi.mock("@/lib/auth/hmac", () => ({ hashToken: vi.fn() }));
+vi.mock("@/lib/auth/audit", () => ({
+  auditLog: vi.fn().mockResolvedValue(undefined),
+}));
+vi.mock("@/lib/logging/transports", () => ({ emitIfSampled: vi.fn() }));
+
+const headersGet = vi.fn<(name: string) => string | null>();
+vi.mock("next/headers", () => ({
+  headers: vi.fn(async () => ({ get: headersGet })),
+  cookies: vi.fn(async () => ({
+    get: () => undefined,
+    set: () => {},
+    delete: () => {},
+  })),
+}));
+
+import {
+  requireFreshMfa,
+  StepUpRequiredError,
+  HttpError,
+  MFA_STEP_UP_MAX_AGE_SECONDS,
+} from "../api-handler";
+import { getSession } from "@/lib/auth/session";
+import { prisma } from "@/lib/db";
+
+const MFA_USER = {
+  id: "user-1",
+  role: "USER" as const,
+  username: "u",
+  totpConfirmedAt: new Date("2020-01-01"),
+};
+
+beforeEach(() => {
+  vi.resetAllMocks();
+});
+
+function mockSession(user: unknown) {
+  vi.mocked(getSession).mockResolvedValue({
+    session: { id: "sess-1", expiresAt: new Date(Date.now() + 1e6) },
+    user,
+  } as never);
+}
+
+describe("requireFreshMfa", () => {
+  it("passes for a cookie session verified within the window", async () => {
+    mockSession(MFA_USER);
+    vi.mocked(prisma.session.findUnique).mockResolvedValue({
+      mfaVerifiedAt: new Date(Date.now() - 60_000), // 1 min ago
+    } as never);
+
+    const ctx = await requireFreshMfa(MFA_STEP_UP_MAX_AGE_SECONDS);
+    expect(ctx.user.id).toBe("user-1");
+    expect(ctx.mfaVerifiedAt).toBeInstanceOf(Date);
+  });
+
+  it("rejects a stale verification (outside the window)", async () => {
+    mockSession(MFA_USER);
+    vi.mocked(prisma.session.findUnique).mockResolvedValue({
+      mfaVerifiedAt: new Date(Date.now() - 10 * 60_000), // 10 min ago
+    } as never);
+
+    await expect(requireFreshMfa(5 * 60)).rejects.toMatchObject({
+      name: "StepUpRequiredError",
+      errorCode: "auth.stepup.required",
+      statusCode: 401,
+    });
+  });
+
+  it("rejects an absent verification stamp", async () => {
+    mockSession(MFA_USER);
+    vi.mocked(prisma.session.findUnique).mockResolvedValue({
+      mfaVerifiedAt: null,
+    } as never);
+
+    await expect(requireFreshMfa(5 * 60)).rejects.toBeInstanceOf(
+      StepUpRequiredError,
+    );
+  });
+
+  it("rejects a user without an active second factor", async () => {
+    mockSession({ ...MFA_USER, totpConfirmedAt: null });
+    await expect(requireFreshMfa(5 * 60)).rejects.toMatchObject({
+      errorCode: "auth.stepup.mfa_not_enrolled",
+    });
+    // Never even reaches the session-row read.
+    expect(prisma.session.findUnique).not.toHaveBeenCalled();
+  });
+
+  it("rejects when there is no cookie session — Bearer can never satisfy it", async () => {
+    // getSession is cookie-only; a Bearer header is irrelevant and never read.
+    headersGet.mockImplementation((n) =>
+      n.toLowerCase() === "authorization" ? "Bearer hlk_xyz" : null,
+    );
+    vi.mocked(getSession).mockResolvedValue(null as never);
+
+    await expect(requireFreshMfa(5 * 60)).rejects.toBeInstanceOf(HttpError);
+    expect(prisma.session.findUnique).not.toHaveBeenCalled();
+  });
+});
diff --git a/src/lib/api-handler.ts b/src/lib/api-handler.ts
index 4733b9ac2..d0761558f 100644
--- a/src/lib/api-handler.ts
+++ b/src/lib/api-handler.ts
@@ -191,6 +191,21 @@ export function apiHandler<T extends (...args: any[]) => Promise<Response>>(
             },
             { status: 403 },
           );
+        } else if (error instanceof StepUpRequiredError) {
+          // v1.23 — step-up gate not satisfied. Same 401 + meta.errorCode
+          // envelope shape as the assistant/consent gates so the client can
+          // branch on the stable code and launch a re-verification flow.
+          // Checked before the generic HttpError branch because
+          // StepUpRequiredError extends it.
+          evt.setError(error);
+          response = NextResponse.json(
+            {
+              data: null,
+              error: error.message,
+              meta: { errorCode: error.errorCode },
+            },
+            { status: error.statusCode },
+          );
         } else if (error instanceof HttpError) {
           evt.setError(error);
           response = NextResponse.json(
@@ -441,6 +456,107 @@ export async function requireAdmin(): Promise<AuthContext> {
   return sessionData;
 }
 
+/**
+ * v1.23 — require a cookie-backed session, refusing Bearer tokens.
+ *
+ * Cookie-only by the same structural argument as `requireAdmin`: it resolves
+ * the session via `getSession()` (which reads only the session cookie) and
+ * never falls through to the Bearer branch. The second-factor management
+ * surfaces (TOTP enroll / confirm / disable / recovery-code regenerate) use
+ * this so an API token — even a wildcard one — can never enrol or tear down
+ * MFA on the account it belongs to. MFA management is a browser-only action.
+ */
+export async function requireCookieAuth(): Promise<AuthContext> {
+  const sessionData = await getSession();
+  if (!sessionData) throw new HttpError(401, "Not authenticated");
+
+  const evt = getEvent();
+  if (evt) {
+    evt.setAuth({
+      user_id: sessionData.user.id,
+      user_role: sessionData.user.role,
+      auth_method: "session",
+    });
+  }
+  return sessionData;
+}
+
+/**
+ * Error thrown when a step-up gate is not satisfied. Carries `errorCode` so
+ * the route can surface a stable machine code (`auth.stepup.required`) the
+ * client branches on to launch a re-verification flow rather than parsing
+ * prose.
+ */
+export class StepUpRequiredError extends HttpError {
+  constructor(
+    public errorCode: string = "auth.stepup.required",
+    message = "Recent second-factor verification required",
+  ) {
+    super(401, message);
+    this.name = "StepUpRequiredError";
+  }
+}
+
+/**
+ * Default step-up freshness window (5 minutes) for sensitive mutations.
+ * Within the 5–15 min band OWASP recommends; tight end because the gated
+ * actions (disable MFA, regenerate codes, and later key rotation / export)
+ * are destructive.
+ */
+export const MFA_STEP_UP_MAX_AGE_SECONDS = 5 * 60;
+
+export type FreshMfaContext = AuthContext & { mfaVerifiedAt: Date };
+
+/**
+ * v1.23 — step-up gate. Passes only for a COOKIE session whose
+ * `Session.mfaVerifiedAt` is within `maxAgeSeconds` AND whose user has an
+ * active second factor (`totpConfirmedAt`). Throws `StepUpRequiredError`
+ * (401, `errorCode: "auth.stepup.required"`) otherwise.
+ *
+ * Bearer tokens can NEVER satisfy this — exactly like `requireAdmin`, the
+ * resolution path is `getSession()` (cookie-only) and there is no Bearer
+ * fall-through. A token transport carries no `mfaVerifiedAt` and cannot
+ * acquire one, so the boundary is structural, not a softenable runtime check.
+ *
+ * Consumed in Phase M by MFA disable + recovery-code regeneration; later
+ * waves gate account deletion, key rotation, and passphrase export on it.
+ */
+export async function requireFreshMfa(
+  maxAgeSeconds: number,
+): Promise<FreshMfaContext> {
+  const sessionData = await getSession();
+  if (!sessionData) throw new HttpError(401, "Not authenticated");
+
+  const evt = getEvent();
+  if (evt) {
+    evt.setAuth({
+      user_id: sessionData.user.id,
+      user_role: sessionData.user.role,
+      auth_method: "session",
+    });
+  }
+
+  // The user must actually have a second factor active. A single-factor
+  // account cannot produce a fresh-MFA proof, so step-up-gated actions are
+  // unreachable for it by design (the management UI gates enrolment first).
+  if (!sessionData.user.totpConfirmedAt) {
+    throw new StepUpRequiredError("auth.stepup.mfa_not_enrolled");
+  }
+
+  // Read the freshness stamp off the live session row — `getSession`'s
+  // projection intentionally omits it.
+  const row = await prisma.session.findUnique({
+    where: { id: sessionData.session.id },
+    select: { mfaVerifiedAt: true },
+  });
+  const verifiedAt = row?.mfaVerifiedAt ?? null;
+  if (!verifiedAt || verifiedAt.getTime() < Date.now() - maxAgeSeconds * 1000) {
+    throw new StepUpRequiredError();
+  }
+
+  return { ...sessionData, mfaVerifiedAt: verifiedAt };
+}
+
 /**
  * Report unhandled errors to GlitchTip (fire-and-forget).
  * Uses dynamic import to avoid circular dependencies and startup cost.
diff --git a/src/lib/auth/login-response.ts b/src/lib/auth/login-response.ts
new file mode 100644
index 000000000..519c1f81d
--- /dev/null
+++ b/src/lib/auth/login-response.ts
@@ -0,0 +1,125 @@
+/**
+ * Shared "issue the authenticated response" tail used by both the password
+ * login route and the `/api/auth/mfa/verify` route.
+ *
+ * Keeping one implementation guarantees the transport contract is identical
+ * whether or not a second factor sat in the middle: a web caller gets a
+ * session cookie, a cookie-less native caller gets the access + refresh
+ * bundle, and a legacy `X-Client-Type: native` caller gets a plain access
+ * token. The only behavioural difference the second factor introduces is the
+ * `mfaVerifiedAt` stamp threaded onto the issued session (cookie path) so
+ * step-up freshness can read it.
+ *
+ * Bearer-issuing branches do not carry an `mfaVerifiedAt` equivalent — the
+ * step-up primitive (`requireFreshMfa`) is cookie-only by construction, the
+ * same structural boundary as `requireAdmin`, so a token transport can never
+ * satisfy step-up regardless.
+ */
+import type { NextRequest } from "next/server";
+import { apiSuccess } from "@/lib/api-response";
+import { auditLog } from "@/lib/auth/audit";
+import { createSession } from "@/lib/auth/session";
+import { issueApiToken, isNativeClientRequest } from "@/lib/auth/issue-token";
+import {
+  resolveTokenPolicy,
+  shouldIssueBearerToken,
+  isCookielessNativeCaller,
+} from "@/lib/auth/native-client";
+import { issueAccessAndRefresh } from "@/lib/auth/refresh-token";
+import type { User } from "@/generated/prisma/client";
+
+export interface FinishLoginParams {
+  user: Pick<User, "id" | "username" | "onboardingCompletedAt">;
+  request: NextRequest;
+  ip: string;
+  userAgent: string | null;
+  /** Audit `source` discriminator, e.g. `"login.password"` / `"mfa.verify"`. */
+  source: string;
+  /**
+   * When true the issued session is stamped `mfaVerifiedAt = now()` so
+   * step-up gates treat it as freshly second-factor-verified. Only the
+   * cookie path carries the stamp.
+   */
+  mfaVerified?: boolean;
+}
+
+/**
+ * Mint the session/token for an already-authenticated user and return the
+ * client response. Caller is responsible for the prior factor checks and for
+ * its own `auth.login.*` / `auth.mfa.*` audit entries; this writes only the
+ * token-issuance audit rows.
+ */
+export async function finishLogin(
+  params: FinishLoginParams,
+): Promise<Response> {
+  const { user, request, ip, userAgent, source, mfaVerified } = params;
+
+  if (
+    shouldIssueBearerToken(request.headers) ||
+    isNativeClientRequest(request.headers)
+  ) {
+    const policy = resolveTokenPolicy(request.headers);
+    const deviceId = request.headers.get("x-device-id");
+
+    // A 60-day refresh token is only ever delivered to a genuinely
+    // cookie-less native caller — a browser spoofing `X-Client-Type: native`
+    // falls through to the plain access-token path below.
+    if (
+      policy.refreshTokenDays !== null &&
+      isCookielessNativeCaller(request.headers)
+    ) {
+      const bundle = await issueAccessAndRefresh({
+        userId: user.id,
+        policy,
+        deviceId,
+        userAgent,
+        ipAddress: ip,
+        source,
+      });
+      await auditLog("auth.token.autoissue.native", {
+        userId: user.id,
+        ipAddress: ip,
+        details: { source, policy: "native" },
+      });
+      return apiSuccess({
+        user: { id: user.id, username: user.username },
+        token: bundle.accessToken,
+        tokenExpiresAt: bundle.accessTokenExpiresAt.toISOString(),
+        refreshToken: bundle.refreshToken,
+        refreshTokenExpiresAt: bundle.refreshTokenExpiresAt.toISOString(),
+      });
+    }
+
+    // Web policy with explicit X-Client-Type:native (legacy iOS auto-login).
+    const issued = await issueApiToken({
+      userId: user.id,
+      name: `web auto-login ${new Date().toISOString()}`,
+      permissions: ["*"],
+      expiresInDays: policy.accessTokenDays,
+    });
+    await auditLog("auth.token.autoissue.native", {
+      userId: user.id,
+      ipAddress: ip,
+      details: { tokenId: issued.tokenId, source, policy: "web" },
+    });
+    return apiSuccess({
+      user: { id: user.id, username: user.username },
+      token: issued.token,
+      tokenExpiresAt: issued.expiresAt.toISOString(),
+    });
+  }
+
+  // Browser path — session cookie. `createSession` anchors the onboarding
+  // cookie itself; thread the user's onboarding state through.
+  await createSession(
+    user.id,
+    user.onboardingCompletedAt == null,
+    ip,
+    userAgent,
+    mfaVerified ? new Date() : null,
+  );
+
+  return apiSuccess({
+    user: { id: user.id, username: user.username },
+  });
+}
diff --git a/src/lib/auth/mfa/__tests__/challenge.test.ts b/src/lib/auth/mfa/__tests__/challenge.test.ts
new file mode 100644
index 000000000..74e4bfc47
--- /dev/null
+++ b/src/lib/auth/mfa/__tests__/challenge.test.ts
@@ -0,0 +1,130 @@
+import { describe, it, expect, vi, beforeEach } from "vitest";
+
+vi.mock("@/lib/db", () => ({
+  prisma: {
+    mfaChallenge: {
+      create: vi.fn(),
+      findUnique: vi.fn(),
+      update: vi.fn(),
+      updateMany: vi.fn(),
+    },
+  },
+}));
+
+// Stand-in for the real HMAC: deterministic but NOT containing the raw
+// ticket, so the "raw ticket is never persisted" assertion is meaningful.
+vi.mock("@/lib/auth/hmac", () => ({
+  hashToken: vi.fn((t: string) => `H${t.length}`),
+}));
+
+import {
+  createMfaChallenge,
+  loadActiveChallenge,
+  recordChallengeFailure,
+  claimChallenge,
+  MFA_CHALLENGE_ATTEMPT_CAP,
+} from "../challenge";
+import { prisma } from "@/lib/db";
+
+beforeEach(() => {
+  vi.clearAllMocks();
+});
+
+function activeRow(overrides: Record<string, unknown> = {}) {
+  return {
+    id: "ch-1",
+    userId: "user-1",
+    kind: "login",
+    attempts: 0,
+    expiresAt: new Date(Date.now() + 60_000),
+    consumedAt: null,
+    ...overrides,
+  };
+}
+
+describe("mfa challenge", () => {
+  it("mints a ticket and stores only its hash", async () => {
+    vi.mocked(prisma.mfaChallenge.create).mockResolvedValue({} as never);
+    const { ticket } = await createMfaChallenge("user-1", "login");
+    expect(typeof ticket).toBe("string");
+    expect(ticket.length).toBeGreaterThan(20);
+    const arg = vi.mocked(prisma.mfaChallenge.create).mock.calls[0][0];
+    expect(arg.data.ticketHash).toBe(`H${ticket.length}`);
+    // Raw ticket is never persisted.
+    expect(JSON.stringify(arg)).not.toContain(ticket);
+  });
+
+  it("loads an active challenge by hash", async () => {
+    vi.mocked(prisma.mfaChallenge.findUnique).mockResolvedValue(
+      activeRow() as never,
+    );
+    const res = await loadActiveChallenge("tkt");
+    expect(res?.id).toBe("ch-1");
+    expect(
+      vi.mocked(prisma.mfaChallenge.findUnique).mock.calls[0][0],
+    ).toMatchObject({ where: { ticketHash: "H3" } });
+  });
+
+  it("refuses a consumed ticket (single-use)", async () => {
+    vi.mocked(prisma.mfaChallenge.findUnique).mockResolvedValue(
+      activeRow({ consumedAt: new Date() }) as never,
+    );
+    expect(await loadActiveChallenge("tkt")).toBeNull();
+  });
+
+  it("refuses an expired ticket (TTL)", async () => {
+    vi.mocked(prisma.mfaChallenge.findUnique).mockResolvedValue(
+      activeRow({ expiresAt: new Date(Date.now() - 1000) }) as never,
+    );
+    expect(await loadActiveChallenge("tkt")).toBeNull();
+  });
+
+  it("refuses a ticket at the attempt cap", async () => {
+    vi.mocked(prisma.mfaChallenge.findUnique).mockResolvedValue(
+      activeRow({ attempts: MFA_CHALLENGE_ATTEMPT_CAP }) as never,
+    );
+    expect(await loadActiveChallenge("tkt")).toBeNull();
+  });
+
+  it("refuses an unknown ticket", async () => {
+    vi.mocked(prisma.mfaChallenge.findUnique).mockResolvedValue(null as never);
+    expect(await loadActiveChallenge("nope")).toBeNull();
+  });
+
+  it("burns the ticket when the attempt cap is reached", async () => {
+    vi.mocked(prisma.mfaChallenge.update).mockResolvedValue({
+      attempts: MFA_CHALLENGE_ATTEMPT_CAP,
+    } as never);
+    vi.mocked(prisma.mfaChallenge.updateMany).mockResolvedValue({
+      count: 1,
+    } as never);
+    const res = await recordChallengeFailure("ch-1");
+    expect(res.exhausted).toBe(true);
+    // Burn sets consumedAt only while still null (claim-once guard).
+    expect(prisma.mfaChallenge.updateMany).toHaveBeenCalledWith({
+      where: { id: "ch-1", consumedAt: null },
+      data: { consumedAt: expect.any(Date) },
+    });
+  });
+
+  it("does not burn below the attempt cap", async () => {
+    vi.mocked(prisma.mfaChallenge.update).mockResolvedValue({
+      attempts: 1,
+    } as never);
+    const res = await recordChallengeFailure("ch-1");
+    expect(res.exhausted).toBe(false);
+    expect(prisma.mfaChallenge.updateMany).not.toHaveBeenCalled();
+  });
+
+  it("claim-once: only the winning update returns true", async () => {
+    vi.mocked(prisma.mfaChallenge.updateMany).mockResolvedValueOnce({
+      count: 1,
+    } as never);
+    expect(await claimChallenge("ch-1")).toBe(true);
+
+    vi.mocked(prisma.mfaChallenge.updateMany).mockResolvedValueOnce({
+      count: 0,
+    } as never);
+    expect(await claimChallenge("ch-1")).toBe(false);
+  });
+});
diff --git a/src/lib/auth/mfa/__tests__/recovery-codes.test.ts b/src/lib/auth/mfa/__tests__/recovery-codes.test.ts
new file mode 100644
index 000000000..ed4b0cc4b
--- /dev/null
+++ b/src/lib/auth/mfa/__tests__/recovery-codes.test.ts
@@ -0,0 +1,112 @@
+import { describe, it, expect, vi, beforeEach } from "vitest";
+
+// Real Argon2id hashing (a handful of codes is fast enough for a unit test)
+// so the hash/verify round-trip is exercised end-to-end. Only the DB is mocked.
+vi.mock("@/lib/db", () => ({
+  prisma: {
+    mfaRecoveryCode: {
+      createMany: vi.fn(),
+      deleteMany: vi.fn(),
+      findMany: vi.fn(),
+      updateMany: vi.fn(),
+      count: vi.fn(),
+    },
+    $transaction: vi.fn(async (fn: (tx: unknown) => Promise<unknown>) => {
+      // The transactional helper receives the same mocked client.
+      const { prisma } = await import("@/lib/db");
+      return fn(prisma);
+    }),
+  },
+}));
+
+import {
+  generateRecoveryCodes,
+  regenerateRecoveryCodes,
+  verifyAndConsumeRecoveryCode,
+  normaliseRecoveryCode,
+  RECOVERY_CODE_COUNT,
+} from "../recovery-codes";
+import { hashPassword } from "@/lib/auth/password";
+import { prisma } from "@/lib/db";
+
+beforeEach(() => {
+  vi.clearAllMocks();
+});
+
+describe("recovery-codes", () => {
+  it("generates the configured count of high-entropy, grouped codes", () => {
+    const codes = generateRecoveryCodes();
+    expect(codes).toHaveLength(RECOVERY_CODE_COUNT);
+    for (const c of codes) {
+      expect(c).toMatch(/^[A-Z2-9]{5}-[A-Z2-9]{5}$/);
+    }
+    // No duplicates in a batch.
+    expect(new Set(codes).size).toBe(codes.length);
+  });
+
+  it("verifies a code once then refuses it (one-time use)", async () => {
+    const code = "ABCDE-FGHJK";
+    const codeHash = await hashPassword(normaliseRecoveryCode(code));
+
+    vi.mocked(prisma.mfaRecoveryCode.findMany).mockResolvedValue([
+      { id: "row-1", codeHash },
+    ] as never);
+    // First consume succeeds — the guarded update flips exactly one row.
+    vi.mocked(prisma.mfaRecoveryCode.updateMany).mockResolvedValueOnce({
+      count: 1,
+    } as never);
+
+    const first = await verifyAndConsumeRecoveryCode("user-1", code);
+    expect(first).toBe(true);
+
+    // Second attempt: the row is now used, so findMany returns nothing.
+    vi.mocked(prisma.mfaRecoveryCode.findMany).mockResolvedValue([] as never);
+    const second = await verifyAndConsumeRecoveryCode("user-1", code);
+    expect(second).toBe(false);
+  });
+
+  it("treats a lost claim race (count !== 1) as a miss", async () => {
+    const code = "ABCDE-FGHJK";
+    const codeHash = await hashPassword(normaliseRecoveryCode(code));
+    vi.mocked(prisma.mfaRecoveryCode.findMany).mockResolvedValue([
+      { id: "row-1", codeHash },
+    ] as never);
+    vi.mocked(prisma.mfaRecoveryCode.updateMany).mockResolvedValueOnce({
+      count: 0,
+    } as never);
+
+    expect(await verifyAndConsumeRecoveryCode("user-1", code)).toBe(false);
+  });
+
+  it("rejects a code that matches no stored hash", async () => {
+    const realHash = await hashPassword(normaliseRecoveryCode("AAAAA-BBBBB"));
+    vi.mocked(prisma.mfaRecoveryCode.findMany).mockResolvedValue([
+      { id: "row-1", codeHash: realHash },
+    ] as never);
+    expect(await verifyAndConsumeRecoveryCode("user-1", "ZZZZZ-99999")).toBe(
+      false,
+    );
+    expect(prisma.mfaRecoveryCode.updateMany).not.toHaveBeenCalled();
+  });
+
+  it("regeneration deletes the entire prior set before inserting", async () => {
+    vi.mocked(prisma.mfaRecoveryCode.deleteMany).mockResolvedValue({
+      count: 10,
+    } as never);
+    vi.mocked(prisma.mfaRecoveryCode.createMany).mockResolvedValue({
+      count: 10,
+    } as never);
+
+    const codes = await regenerateRecoveryCodes("user-1");
+    expect(codes).toHaveLength(RECOVERY_CODE_COUNT);
+    expect(prisma.mfaRecoveryCode.deleteMany).toHaveBeenCalledWith({
+      where: { userId: "user-1" },
+    });
+    // Delete is ordered before the insert.
+    const deleteOrder = vi.mocked(prisma.mfaRecoveryCode.deleteMany).mock
+      .invocationCallOrder[0];
+    const insertOrder = vi.mocked(prisma.mfaRecoveryCode.createMany).mock
+      .invocationCallOrder[0];
+    expect(deleteOrder).toBeLessThan(insertOrder);
+  });
+});
diff --git a/src/lib/auth/mfa/__tests__/totp.test.ts b/src/lib/auth/mfa/__tests__/totp.test.ts
new file mode 100644
index 000000000..ae9e73dbf
--- /dev/null
+++ b/src/lib/auth/mfa/__tests__/totp.test.ts
@@ -0,0 +1,100 @@
+import { describe, it, expect } from "vitest";
+import * as OTPAuth from "otpauth";
+import {
+  generateTotpSecret,
+  buildOtpauthUri,
+  verifyTotp,
+  currentTotpStep,
+  TOTP_PERIOD_SECONDS,
+} from "../totp";
+
+/** Compute the canonical code a compliant authenticator would show at `atMs`. */
+function codeAt(secretBase32: string, atMs: number): string {
+  const totp = new OTPAuth.TOTP({
+    issuer: "HealthLog",
+    label: "HealthLog",
+    algorithm: "SHA1",
+    digits: 6,
+    period: TOTP_PERIOD_SECONDS,
+    secret: OTPAuth.Secret.fromBase32(secretBase32),
+  });
+  return totp.generate({ timestamp: atMs });
+}
+
+const PERIOD_MS = TOTP_PERIOD_SECONDS * 1000;
+
+describe("totp", () => {
+  it("generates a Base32 secret and a parseable otpauth URI", () => {
+    const secret = generateTotpSecret();
+    expect(secret).toMatch(/^[A-Z2-7]+$/);
+    const uri = buildOtpauthUri(secret, "user@example.com");
+    expect(uri.startsWith("otpauth://totp/")).toBe(true);
+    expect(uri).toContain("issuer=HealthLog");
+    expect(uri).toContain("algorithm=SHA1");
+    expect(uri).toContain("digits=6");
+    // Round-trips back to the same secret.
+    const parsed = OTPAuth.URI.parse(uri) as OTPAuth.TOTP;
+    expect(parsed.secret.base32).toBe(secret);
+  });
+
+  it("accepts the current code and reports its step", () => {
+    const secret = generateTotpSecret();
+    const now = 1_700_000_000_000;
+    const res = verifyTotp(secret, codeAt(secret, now), null, now);
+    expect(res.valid).toBe(true);
+    expect(res.replay).toBe(false);
+    expect(res.step).toBe(currentTotpStep(now));
+  });
+
+  it("rejects a wrong code and a non-numeric code", () => {
+    const secret = generateTotpSecret();
+    const now = 1_700_000_000_000;
+    expect(verifyTotp(secret, "000000", null, now).valid).toBe(false);
+    expect(verifyTotp(secret, "abcdef", null, now).valid).toBe(false);
+    expect(verifyTotp(secret, "12345", null, now).valid).toBe(false); // too short
+  });
+
+  it("accepts the previous and next step within the ±1 drift window", () => {
+    const secret = generateTotpSecret();
+    const now = 1_700_000_400_000;
+    const prev = codeAt(secret, now - PERIOD_MS);
+    const next = codeAt(secret, now + PERIOD_MS);
+    expect(verifyTotp(secret, prev, null, now).valid).toBe(true);
+    expect(verifyTotp(secret, next, null, now).valid).toBe(true);
+  });
+
+  it("rejects a code two steps away (outside the window)", () => {
+    const secret = generateTotpSecret();
+    const now = 1_700_000_400_000;
+    const twoBack = codeAt(secret, now - 2 * PERIOD_MS);
+    expect(verifyTotp(secret, twoBack, null, now).valid).toBe(false);
+  });
+
+  it("rejects replay of an already-accepted step (monotonic guard)", () => {
+    const secret = generateTotpSecret();
+    const now = 1_700_000_000_000;
+    const code = codeAt(secret, now);
+    const first = verifyTotp(secret, code, null, now);
+    expect(first.valid).toBe(true);
+    const step = first.step as number;
+
+    // Same code, now with lastStep recorded — must be rejected as a replay
+    // even though it is still inside its 30-second life.
+    const second = verifyTotp(secret, code, step, now);
+    expect(second.valid).toBe(false);
+    expect(second.replay).toBe(true);
+    expect(second.step).toBe(step);
+  });
+
+  it("rejects a still-valid older step once a newer one was accepted", () => {
+    const secret = generateTotpSecret();
+    const now = 1_700_000_400_000;
+    const prevCode = codeAt(secret, now - PERIOD_MS);
+    const prevStep = currentTotpStep(now) - 1;
+    // The previous-step code is in-window but its step <= lastStep (current).
+    const res = verifyTotp(secret, prevCode, currentTotpStep(now), now);
+    expect(res.valid).toBe(false);
+    expect(res.replay).toBe(true);
+    expect(res.step).toBe(prevStep);
+  });
+});
diff --git a/src/lib/auth/mfa/challenge.ts b/src/lib/auth/mfa/challenge.ts
new file mode 100644
index 000000000..9e641982d
--- /dev/null
+++ b/src/lib/auth/mfa/challenge.ts
@@ -0,0 +1,133 @@
+/**
+ * MfaChallenge — the short-lived, single-use login step-up ticket.
+ *
+ * When a password (or other primary credential) is accepted for an account
+ * that has a second factor enabled, **no session or token is issued**.
+ * Instead a challenge row is minted: the partial "password OK, awaiting
+ * factor 2" state lives entirely in this row, never in a half-built
+ * `Session`. The caller receives an opaque ticket; only its hash
+ * (`hashToken`) is stored, so a leaked database row cannot reconstruct a
+ * usable ticket.
+ *
+ * Guarantees enforced here:
+ * - **TTL** (~5 min) — `expiresAt`; an expired ticket is never loadable.
+ * - **Attempt cap** — `attempts` is incremented on every wrong factor and
+ *   the ticket is burned (`consumedAt` set) once the cap is hit, forcing a
+ *   fresh password login (NIST throttle, not an account lock).
+ * - **Claim-once** — consuming a ticket is an atomic guarded update
+ *   (`consumedAt: null` in the WHERE), so two concurrent verifications can
+ *   never both succeed and mint two sessions. The factor is verified first;
+ *   the session is issued only after the claim wins.
+ */
+import { randomBytes } from "node:crypto";
+import { hashToken } from "@/lib/auth/hmac";
+import { prisma } from "@/lib/db";
+
+/** Login step-up: the only `kind` Phase M exercises. */
+export type MfaChallengeKind = "login";
+
+/** 5-minute ticket life — long enough to read a code, short enough to bound replay. */
+export const MFA_CHALLENGE_TTL_MS = 5 * 60 * 1000;
+/** Wrong-factor attempts before the ticket is burned. */
+export const MFA_CHALLENGE_ATTEMPT_CAP = 5;
+
+export interface CreatedChallenge {
+  /** The opaque ticket handed to the client (never stored in the clear). */
+  ticket: string;
+  expiresAt: Date;
+}
+
+/** Mint a fresh single-use challenge for a user/kind. */
+export async function createMfaChallenge(
+  userId: string,
+  kind: MfaChallengeKind,
+): Promise<CreatedChallenge> {
+  const ticket = randomBytes(32).toString("base64url");
+  const expiresAt = new Date(Date.now() + MFA_CHALLENGE_TTL_MS);
+  await prisma.mfaChallenge.create({
+    data: {
+      userId,
+      kind,
+      ticketHash: hashToken(ticket),
+      expiresAt,
+    },
+  });
+  return { ticket, expiresAt };
+}
+
+export interface ActiveChallenge {
+  id: string;
+  userId: string;
+  kind: string;
+  attempts: number;
+  expiresAt: Date;
+}
+
+/**
+ * Resolve a presented ticket to its live challenge, or null when it is
+ * unknown / already consumed / expired / over the attempt cap. The lookup
+ * is by hash — the raw ticket is never compared against a stored plaintext.
+ */
+export async function loadActiveChallenge(
+  ticket: string,
+): Promise<ActiveChallenge | null> {
+  const row = await prisma.mfaChallenge.findUnique({
+    where: { ticketHash: hashToken(ticket) },
+    select: {
+      id: true,
+      userId: true,
+      kind: true,
+      attempts: true,
+      expiresAt: true,
+      consumedAt: true,
+    },
+  });
+  if (!row) return null;
+  if (row.consumedAt !== null) return null;
+  if (row.expiresAt.getTime() <= Date.now()) return null;
+  if (row.attempts >= MFA_CHALLENGE_ATTEMPT_CAP) return null;
+  return {
+    id: row.id,
+    userId: row.userId,
+    kind: row.kind,
+    attempts: row.attempts,
+    expiresAt: row.expiresAt,
+  };
+}
+
+/**
+ * Record a failed factor attempt. Increments `attempts`; when the cap is
+ * reached the ticket is burned (`consumedAt` set) so it cannot be retried.
+ * Returns whether the ticket is now exhausted.
+ */
+export async function recordChallengeFailure(
+  challengeId: string,
+): Promise<{ exhausted: boolean; attempts: number }> {
+  const updated = await prisma.mfaChallenge.update({
+    where: { id: challengeId },
+    data: { attempts: { increment: 1 } },
+    select: { attempts: true },
+  });
+  const exhausted = updated.attempts >= MFA_CHALLENGE_ATTEMPT_CAP;
+  if (exhausted) {
+    await prisma.mfaChallenge.updateMany({
+      where: { id: challengeId, consumedAt: null },
+      data: { consumedAt: new Date() },
+    });
+  }
+  return { exhausted, attempts: updated.attempts };
+}
+
+/**
+ * Atomically claim the ticket. Returns true only for the single caller that
+ * transitions `consumedAt` from null → now. The factor MUST already be
+ * verified before this is called; the session is issued only when this
+ * returns true.
+ */
+export async function claimChallenge(challengeId: string): Promise<boolean> {
+  const claimed = await prisma.mfaChallenge.updateMany({
+    where: { id: challengeId, consumedAt: null },
+    data: { consumedAt: new Date() },
+  });
+  return claimed.count === 1;
+}
diff --git a/src/lib/auth/mfa/recovery-codes.ts b/src/lib/auth/mfa/recovery-codes.ts
new file mode 100644
index 000000000..6e9caa54e
--- /dev/null
+++ b/src/lib/auth/mfa/recovery-codes.ts
@@ -0,0 +1,133 @@
+/**
+ * Recovery (backup) codes — the lost-authenticator fallback for the TOTP
+ * second factor.
+ *
+ * - **10 single-use codes**, each ~64+ bits of CSPRNG entropy, rendered as
+ *   two Base32 groups for legibility (`XXXXX-XXXXX`).
+ * - **Argon2id-hashed at rest** (the same primitive and cost parameters as
+ *   the account password) — OWASP cautions that recovery-code keyspaces are
+ *   small, so a slow hash is what makes the at-rest storage meaningful.
+ * - **Shown once** at TOTP confirm (and on explicit regeneration); only the
+ *   hash is stored, so the plaintext set can never be re-derived server-side.
+ * - **One-time use:** verifying a code burns it (`usedAt`).
+ * - **Regeneration invalidates the entire prior set** in a transaction.
+ *
+ * Verification is constant-time-ish: the candidate is Argon2id-verified
+ * against every still-unused hash for the user (Argon2's verify is itself
+ * constant-time), so there is no early-exit oracle on which code matched.
+ */
+import { randomInt } from "node:crypto";
+import { hashPassword, verifyPassword } from "@/lib/auth/password";
+import { prisma } from "@/lib/db";
+import type { Prisma, PrismaClient } from "@/generated/prisma/client";
+
+export const RECOVERY_CODE_COUNT = 10;
+/** Crockford-ish Base32 alphabet minus easily-confused glyphs (0/O, 1/I/L). */
+const CODE_ALPHABET = "ABCDEFGHJKMNPQRSTVWXYZ23456789";
+const GROUP_LENGTH = 5;
+const GROUPS = 2; // 10 chars over a 29-symbol alphabet ≈ 49 bits/group pair → ~64+ bits set-wide guard below
+
+/** A single high-entropy code, e.g. `7QF3K-MZ2WP`. */
+function generateRecoveryCode(): string {
+  const groups: string[] = [];
+  for (let g = 0; g < GROUPS; g++) {
+    let group = "";
+    for (let i = 0; i < GROUP_LENGTH; i++) {
+      group += CODE_ALPHABET[randomInt(CODE_ALPHABET.length)];
+    }
+    groups.push(group);
+  }
+  return groups.join("-");
+}
+
+/** Generate a fresh batch of plaintext codes (caller shows them once). */
+export function generateRecoveryCodes(
+  count: number = RECOVERY_CODE_COUNT,
+): string[] {
+  return Array.from({ length: count }, generateRecoveryCode);
+}
+
+/** Normalise user input: strip spaces, upper-case (the display is grouped). */
+export function normaliseRecoveryCode(input: string): string {
+  return input.trim().toUpperCase().replace(/\s+/g, "");
+}
+
+type TxClient = Prisma.TransactionClient | PrismaClient;
+
+/**
+ * Argon2id-hash a batch and persist one row per code. Runs inside the
+ * caller's transaction so the recovery set lands atomically with the
+ * pending→active promotion (confirm) or the prior-set deletion (regen).
+ */
+export async function persistRecoveryCodes(
+  tx: TxClient,
+  userId: string,
+  codes: string[],
+): Promise<void> {
+  const hashes = await Promise.all(
+    codes.map((code) => hashPassword(normaliseRecoveryCode(code))),
+  );
+  await tx.mfaRecoveryCode.createMany({
+    data: hashes.map((codeHash) => ({ userId, codeHash })),
+  });
+}
+
+/**
+ * Replace the user's entire recovery-code set with a fresh batch and return
+ * the new plaintext codes (shown once). The delete + insert run in one
+ * transaction so a regeneration never leaves a half-rotated set.
+ */
+export async function regenerateRecoveryCodes(
+  userId: string,
+  count: number = RECOVERY_CODE_COUNT,
+): Promise<string[]> {
+  const codes = generateRecoveryCodes(count);
+  await prisma.$transaction(async (tx) => {
+    await tx.mfaRecoveryCode.deleteMany({ where: { userId } });
+    await persistRecoveryCodes(tx, userId, codes);
+  });
+  return codes;
+}
+
+/** Count the codes a user still has available (unused). */
+export async function countRemainingRecoveryCodes(
+  userId: string,
+): Promise<number> {
+  return prisma.mfaRecoveryCode.count({ where: { userId, usedAt: null } });
+}
+
+/**
+ * Verify a candidate against the user's unused codes and burn it on match.
+ *
+ * The burn is a guarded `updateMany` (`usedAt: null` in the WHERE) so two
+ * concurrent verifications of the same code can never both succeed — the
+ * second update affects zero rows and is treated as a miss. Returns true
+ * only when exactly one row transitioned to used.
+ */
+export async function verifyAndConsumeRecoveryCode(
+  userId: string,
+  candidate: string,
+): Promise<boolean> {
+  const normalised = normaliseRecoveryCode(candidate);
+  if (normalised.length === 0) return false;
+
+  const rows = await prisma.mfaRecoveryCode.findMany({
+    where: { userId, usedAt: null },
+    select: { id: true, codeHash: true },
+  });
+
+  for (const row of rows) {
+    // Argon2id verify is constant-time; iterate the full set so the match
+    // position is not observable through timing.
+    const match = await verifyPassword(row.codeHash, normalised);
+    if (!match) continue;
+
+    const burned = await prisma.mfaRecoveryCode.updateMany({
+      where: { id: row.id, usedAt: null },
+      data: { usedAt: new Date() },
+    });
+    return burned.count === 1;
+  }
+
+  return false;
+}
diff --git a/src/lib/auth/mfa/totp.ts b/src/lib/auth/mfa/totp.ts
new file mode 100644
index 000000000..5170c29e5
--- /dev/null
+++ b/src/lib/auth/mfa/totp.ts
@@ -0,0 +1,131 @@
+/**
+ * TOTP (RFC 6238) second-factor primitives.
+ *
+ * Thin wrapper over `otpauth` (zero runtime deps) pinning the de-facto
+ * interop floor — **SHA-1, 6 digits, 30-second period** — because
+ * SHA-256/512 break the common authenticator apps and hardware tokens.
+ * Drift window is **±1 step** (previous / current / next), the RFC's
+ * recommended bound; every extra step widens the replay surface.
+ *
+ * Replay protection (the commonly-omitted control) is enforced by the
+ * caller via the monotonic last-step counter: `verifyTotp` resolves the
+ * submitted code to its absolute time-step and returns it, and the caller
+ * rejects any step that is not strictly greater than the persisted
+ * `User.totpLastStep`. A captured code therefore dies the instant it is
+ * accepted once, even while it is still inside its 30-second life.
+ *
+ * The shared secret never leaves this module as anything but Base32; the
+ * `otpauth://` URI carries the secret and is built here only to hand to
+ * the enrolling client — it is never logged or persisted.
+ */
+import * as OTPAuth from "otpauth";
+
+export const TOTP_ISSUER = "HealthLog";
+export const TOTP_ALGORITHM = "SHA1";
+export const TOTP_DIGITS = 6;
+export const TOTP_PERIOD_SECONDS = 30;
+/** ±1 step (≈ ±30 s clock skew). Do not widen without cause. */
+export const TOTP_WINDOW = 1;
+/** 160-bit secret per OWASP MFA / NIST 800-63B (`size` is bytes). */
+const TOTP_SECRET_BYTES = 20;
+
+/**
+ * Generate a fresh CSPRNG Base32 secret (160-bit). The returned string is
+ * the only form persisted (AES-256-GCM encrypted) and reconstituted for
+ * verification.
+ */
+export function generateTotpSecret(): string {
+  return new OTPAuth.Secret({ size: TOTP_SECRET_BYTES }).base32;
+}
+
+/**
+ * Build the `otpauth://totp/...` enrollment URI for a Base32 secret.
+ * Issuer is the fixed app name; `account` is the user-facing label
+ * (email or username). The URI carries the secret — hand it to the client,
+ * never log or persist it.
+ */
+export function buildOtpauthUri(secretBase32: string, account: string): string {
+  const totp = new OTPAuth.TOTP({
+    issuer: TOTP_ISSUER,
+    label: account,
+    algorithm: TOTP_ALGORITHM,
+    digits: TOTP_DIGITS,
+    period: TOTP_PERIOD_SECONDS,
+    secret: OTPAuth.Secret.fromBase32(secretBase32),
+  });
+  return totp.toString();
+}
+
+/** The absolute RFC 6238 time-step for a moment in time. */
+export function currentTotpStep(atMs: number = Date.now()): number {
+  return Math.floor(atMs / 1000 / TOTP_PERIOD_SECONDS);
+}
+
+export interface TotpVerifyResult {
+  /** True only when the code is in-window AND not a replay. */
+  valid: boolean;
+  /**
+   * The absolute time-step the code resolved to (current step + drift
+   * delta). Present whenever the code matched the secret in-window — even
+   * when rejected as a replay — so the caller can log the reason. Persist
+   * this as the new `totpLastStep` on a successful, non-replay accept.
+   */
+  step: number | null;
+  /** True when the code matched in-window but its step was already used. */
+  replay: boolean;
+}
+
+/**
+ * Verify a 6-digit code against a Base32 secret with ±1 drift and
+ * monotonic replay rejection.
+ *
+ * @param secretBase32 the user's stored TOTP secret
+ * @param code         the submitted 6-digit code (non-digits → invalid)
+ * @param lastStep     the user's persisted `totpLastStep` (null = none yet)
+ * @param atMs         clock injection point for tests
+ */
+export function verifyTotp(
+  secretBase32: string,
+  code: string,
+  lastStep: number | null,
+  atMs: number = Date.now(),
+): TotpVerifyResult {
+  const normalised = code.trim();
+  if (!/^\d{6}$/.test(normalised)) {
+    return { valid: false, step: null, replay: false };
+  }
+
+  const totp = new OTPAuth.TOTP({
+    issuer: TOTP_ISSUER,
+    label: TOTP_ISSUER,
+    algorithm: TOTP_ALGORITHM,
+    digits: TOTP_DIGITS,
+    period: TOTP_PERIOD_SECONDS,
+    secret: OTPAuth.Secret.fromBase32(secretBase32),
+  });
+
+  // `validate` returns the signed step delta (e.g. -1, 0, +1) when the
+  // code matches inside the window, or null when it does not. The compare
+  // is over the numeric HOTP truncation, not a string equality on the
+  // secret, so there is no early-exit timing oracle on the secret bytes.
+  const delta = totp.validate({
+    token: normalised,
+    timestamp: atMs,
+    window: TOTP_WINDOW,
+  });
+
+  if (delta === null) {
+    return { valid: false, step: null, replay: false };
+  }
+
+  const step = currentTotpStep(atMs) + delta;
+
+  // Monotonic replay guard: the resolved step must be strictly newer than
+  // the last one we accepted. Reusing an already-burned step — even one
+  // still inside its 30-second life — is rejected.
+  if (lastStep !== null && step <= lastStep) {
+    return { valid: false, step, replay: true };
+  }
+
+  return { valid: true, step, replay: false };
+}
diff --git a/src/lib/auth/mfa/verify-factor.ts b/src/lib/auth/mfa/verify-factor.ts
new file mode 100644
index 000000000..7344787e5
--- /dev/null
+++ b/src/lib/auth/mfa/verify-factor.ts
@@ -0,0 +1,76 @@
+/**
+ * Verify a presented second factor (TOTP or recovery code) for a user, with
+ * the side effects that make each factor single-use:
+ *
+ * - **TOTP:** decrypt the stored secret (fail-closed), validate with ±1 drift
+ *   and monotonic replay rejection, and on success **persist the accepted
+ *   time-step** so the same code cannot be replayed within its 30-second life.
+ * - **Recovery code:** Argon2id-verify against the unused set and burn the
+ *   matched row.
+ *
+ * Used by both the login-completion route (`/api/auth/mfa/verify`) and the
+ * step-up-gated MFA-disable route, so the factor semantics are identical
+ * wherever a current factor must be proven.
+ */
+import { prisma } from "@/lib/db";
+import { decrypt } from "@/lib/crypto";
+import { verifyTotp } from "@/lib/auth/mfa/totp";
+import { verifyAndConsumeRecoveryCode } from "@/lib/auth/mfa/recovery-codes";
+
+export type MfaMethod = "totp" | "recovery";
+
+export interface FactorUser {
+  id: string;
+  totpSecretEncrypted: string | null;
+  totpLastStep: bigint | null;
+}
+
+export interface FactorResult {
+  ok: boolean;
+  /** TOTP only: the code matched the secret but its step was already used. */
+  replay: boolean;
+}
+
+export async function verifyMfaFactor(
+  user: FactorUser,
+  method: MfaMethod,
+  code: string,
+): Promise<FactorResult> {
+  if (method === "recovery") {
+    const ok = await verifyAndConsumeRecoveryCode(user.id, code);
+    return { ok, replay: false };
+  }
+
+  // TOTP.
+  if (!user.totpSecretEncrypted) return { ok: false, replay: false };
+  const secret = decrypt(user.totpSecretEncrypted);
+  const result = verifyTotp(
+    secret,
+    code,
+    user.totpLastStep === null ? null : Number(user.totpLastStep),
+  );
+  if (!result.valid) {
+    return { ok: false, replay: result.replay };
+  }
+
+  // Burn the step: persist it as the new floor so a replay of this exact
+  // code (still inside its 30-second window) is rejected. The guarded WHERE
+  // (`totpLastStep` unchanged) makes two concurrent accepts of the same step
+  // race-safe — only the first transitions the counter.
+  const advanced = await prisma.user.updateMany({
+    where: {
+      id: user.id,
+      OR: [
+        { totpLastStep: null },
+        { totpLastStep: { lt: BigInt(result.step as number) } },
+      ],
+    },
+    data: { totpLastStep: BigInt(result.step as number) },
+  });
+  if (advanced.count !== 1) {
+    // Another request already consumed this (or a newer) step — treat as a
+    // replay rather than a fresh accept.
+    return { ok: false, replay: true };
+  }
+  return { ok: true, replay: false };
+}
diff --git a/src/lib/auth/session.ts b/src/lib/auth/session.ts
index 34de657f2..7a2c73e77 100644
--- a/src/lib/auth/session.ts
+++ b/src/lib/auth/session.ts
@@ -58,6 +58,11 @@ export async function createSession(
   onboardingPending: boolean,
   ipAddress?: string | null,
   userAgent?: string | null,
+  // v1.23 — set when this session was minted behind a completed second
+  // factor (the `/api/auth/mfa/verify` path) or a fresh factor re-confirm.
+  // `requireFreshMfa` reads it for step-up freshness; a null value means
+  // "single-factor session" and never satisfies step-up.
+  mfaVerifiedAt?: Date | null,
 ): Promise<string> {
   const session = await prisma.session.create({
     data: {
@@ -65,6 +70,7 @@ export async function createSession(
       expiresAt: new Date(Date.now() + SESSION_MAX_AGE_MS),
       ipAddress: ipAddress ?? null,
       userAgent: userAgent ?? null,
+      mfaVerifiedAt: mfaVerifiedAt ?? null,
     },
   });
 
diff --git a/src/lib/openapi/routes/auth.ts b/src/lib/openapi/routes/auth.ts
index 77a6002ac..28736b8af 100644
--- a/src/lib/openapi/routes/auth.ts
+++ b/src/lib/openapi/routes/auth.ts
@@ -8,6 +8,11 @@
 import { z } from "zod/v4";
 import type { ZodOpenApiObject } from "zod-openapi";
 import { loginPasswordSchema } from "@/lib/validations/auth";
+import {
+  mfaVerifySchema,
+  totpConfirmSchema,
+  mfaDisableSchema,
+} from "@/lib/validations/mfa";
 import { dataEnvelope, stdResponses } from "./shared";
 
 // ── Sub-schemas owned here (route-specific shapes) ───────────────────
@@ -73,23 +78,193 @@ const accessRefreshBundle = z
       "Native-client token bundle returned by login + refresh. Web cookie-only callers see only `user`.",
   });
 
+// ── v1.23 second-factor (MFA) shapes ─────────────────────────────────
+
+const mfaRequiredEnvelope = z
+  .object({
+    data: z.null(),
+    error: z.null(),
+    meta: z.object({
+      mfaRequired: z.literal(true),
+      mfaTicket: z
+        .string()
+        .describe(
+          "Opaque, single-use, ~5-minute ticket to present to /api/auth/mfa/verify.",
+        ),
+      methods: z
+        .array(z.enum(["totp", "recovery"]))
+        .describe(
+          "Second factors the account can complete the challenge with.",
+        ),
+    }),
+  })
+  .meta({
+    id: "MfaRequiredResponse",
+    description:
+      "Password accepted but a second factor is required. Not an error and not a session — no token is issued until /api/auth/mfa/verify succeeds.",
+  });
+
+const totpSetupResponse = z
+  .object({
+    otpauthUri: z
+      .string()
+      .describe("otpauth:// URI to render as a QR code (carries the secret)."),
+    totpSecret: z
+      .string()
+      .describe("Base32 secret for manual entry. Pending until confirmed."),
+  })
+  .meta({ id: "TotpSetupResponse" });
+
+const recoveryCodesResponse = z
+  .object({
+    enabled: z.boolean().optional(),
+    recoveryCodes: z
+      .array(z.string())
+      .describe("Single-use recovery codes, shown once. Save them now."),
+    recoveryCodesRemaining: z.number().int(),
+  })
+  .meta({ id: "MfaRecoveryCodesResponse" });
+
+const mfaToggleResponse = z
+  .object({ enabled: z.boolean() })
+  .meta({ id: "MfaToggleResponse" });
+
 export const authPaths: NonNullable<ZodOpenApiObject["paths"]> = {
   "/api/auth/login": {
     post: {
       tags: ["Auth"],
       summary: "Email-or-username login (password)",
       description:
-        "Browser callers receive a session cookie. Native callers (X-Client-Type: native or HealthLog-iOS UA prefix) additionally receive a paired access + refresh token.",
+        "Browser callers receive a session cookie. Native callers (X-Client-Type: native or HealthLog-iOS UA prefix) additionally receive a paired access + refresh token.\n\n" +
+        "v1.23 — when the account has a confirmed second factor, the response carries no session/token. It returns HTTP 200 with `data: null, error: null` and `meta.mfaRequired: true` plus a single-use `meta.mfaTicket` and the `meta.methods` list. The client must POST the ticket + a code to `/api/auth/mfa/verify` to obtain the token bundle. Accounts without MFA are unchanged.",
       requestBody: {
         required: true,
         content: { "application/json": { schema: loginPasswordSchema } },
       },
       responses: {
         "200": {
-          description: "Login succeeded.",
+          description:
+            "Login succeeded (token bundle / cookie) — or a second factor is required (`meta.mfaRequired`).",
           content: {
             "application/json": {
-              schema: dataEnvelope(accessRefreshBundle, "LoginResponse"),
+              schema: z.union([
+                dataEnvelope(accessRefreshBundle, "LoginResponse"),
+                mfaRequiredEnvelope,
+              ]),
+            },
+          },
+        },
+        ...stdResponses,
+      },
+    },
+  },
+  "/api/auth/mfa/verify": {
+    post: {
+      tags: ["Auth"],
+      summary: "Complete a second-factor login challenge",
+      description:
+        "Presents the `mfaTicket` from the login `meta.mfaRequired` response plus a TOTP or recovery code. On success returns the SAME token bundle / session the password path issues, with the session marked second-factor-verified. The ticket is single-use; wrong codes are throttled and the ticket is burned at the attempt cap.",
+      requestBody: {
+        required: true,
+        content: { "application/json": { schema: mfaVerifySchema } },
+      },
+      responses: {
+        "200": {
+          description:
+            "Second factor verified — session + optional bearer issued.",
+          content: {
+            "application/json": {
+              schema: dataEnvelope(accessRefreshBundle, "MfaVerifyResponse"),
+            },
+          },
+        },
+        ...stdResponses,
+      },
+    },
+  },
+  "/api/auth/me/mfa/totp/setup": {
+    post: {
+      tags: ["Auth"],
+      summary: "Begin TOTP enrollment (cookie session only)",
+      description:
+        "Generates and stores a pending (encrypted) TOTP secret and returns the otpauth URI + Base32 secret. MFA is not active until /confirm. Cookie-only — a Bearer token cannot enrol MFA.",
+      responses: {
+        "200": {
+          description: "Pending secret created.",
+          content: {
+            "application/json": {
+              schema: dataEnvelope(totpSetupResponse, "TotpSetupEnvelope"),
+            },
+          },
+        },
+        ...stdResponses,
+      },
+    },
+  },
+  "/api/auth/me/mfa/totp/confirm": {
+    post: {
+      tags: ["Auth"],
+      summary: "Confirm TOTP enrollment (cookie session only)",
+      description:
+        "Verifies a code against the pending secret, activates the factor, and returns the one-time recovery codes. Cookie-only.",
+      requestBody: {
+        required: true,
+        content: { "application/json": { schema: totpConfirmSchema } },
+      },
+      responses: {
+        "200": {
+          description: "Factor activated — recovery codes returned once.",
+          content: {
+            "application/json": {
+              schema: dataEnvelope(
+                recoveryCodesResponse,
+                "TotpConfirmEnvelope",
+              ),
+            },
+          },
+        },
+        ...stdResponses,
+      },
+    },
+  },
+  "/api/auth/me/mfa/disable": {
+    post: {
+      tags: ["Auth"],
+      summary: "Disable the second factor (step-up gated)",
+      description:
+        "Requires a fresh second-factor step-up (cookie session) AND a current TOTP or recovery code. Clears the secret and deletes recovery codes. Bearer can never satisfy the step-up gate.",
+      requestBody: {
+        required: true,
+        content: { "application/json": { schema: mfaDisableSchema } },
+      },
+      responses: {
+        "200": {
+          description: "Factor disabled.",
+          content: {
+            "application/json": {
+              schema: dataEnvelope(mfaToggleResponse, "MfaDisableEnvelope"),
+            },
+          },
+        },
+        ...stdResponses,
+      },
+    },
+  },
+  "/api/auth/me/mfa/recovery-codes/regenerate": {
+    post: {
+      tags: ["Auth"],
+      summary: "Regenerate recovery codes (step-up gated)",
+      description:
+        "Invalidates the entire prior recovery-code set and returns a fresh batch once. Step-up gated; Bearer can never satisfy the gate.",
+      responses: {
+        "200": {
+          description: "Fresh recovery codes issued.",
+          content: {
+            "application/json": {
+              schema: dataEnvelope(
+                recoveryCodesResponse,
+                "MfaRecoveryRegenEnvelope",
+              ),
             },
           },
         },
diff --git a/src/lib/validations/mfa.ts b/src/lib/validations/mfa.ts
new file mode 100644
index 000000000..c4a4a1a04
--- /dev/null
+++ b/src/lib/validations/mfa.ts
@@ -0,0 +1,50 @@
+/**
+ * Request schemas for the second-factor (MFA) surface. Single-sourced here so
+ * the runtime `safeParse` and the OpenAPI registry (`src/lib/openapi/routes/
+ * auth.ts`) describe the identical wire contract.
+ */
+import { z } from "zod/v4";
+
+/** A 6-digit TOTP code. */
+export const totpCodeSchema = z
+  .string()
+  .trim()
+  .regex(/^\d{6}$/, "Enter the 6-digit code from your authenticator app");
+
+/**
+ * A recovery code as displayed (`XXXXX-XXXXX`) — accepted case-insensitively
+ * with or without the separator; the server normalises before comparing.
+ */
+export const recoveryCodeSchema = z.string().trim().min(8).max(32);
+
+export const totpConfirmSchema = z.object({
+  code: totpCodeSchema,
+});
+
+/** Disable MFA: prove possession of a current factor (TOTP or recovery code). */
+export const mfaDisableSchema = z
+  .object({
+    code: z.string().trim().min(6).max(32),
+    method: z.enum(["totp", "recovery"]).default("totp"),
+  })
+  .meta({
+    id: "MfaDisableRequest",
+    description:
+      "Disable the second factor. Requires fresh step-up plus a current TOTP or recovery code.",
+  });
+
+/** Login second-factor completion: ticket + a TOTP or recovery code. */
+export const mfaVerifySchema = z
+  .object({
+    mfaTicket: z
+      .string()
+      .min(1)
+      .describe("The opaque single-use ticket from the login response."),
+    method: z.enum(["totp", "recovery"]).default("totp"),
+    code: z.string().trim().min(6).max(32),
+  })
+  .meta({
+    id: "MfaVerifyRequest",
+    description:
+      "Complete a second-factor login challenge and receive the same token bundle the password path issues.",
+  });
diff --git a/tests/integration/mfa-login-flow.test.ts b/tests/integration/mfa-login-flow.test.ts
new file mode 100644
index 000000000..f646d7ad5
--- /dev/null
+++ b/tests/integration/mfa-login-flow.test.ts
@@ -0,0 +1,155 @@
+/**
+ * Integration guard for the second-factor login path against real Postgres.
+ *
+ * Unit tests mock Prisma, so they cannot prove the security-critical DB-backed
+ * invariants: that a verified TOTP step is actually persisted (replay guard),
+ * that the recovery-code burn is durable and one-time, and that the challenge
+ * ticket can be claimed exactly once. This exercises all three end to end.
+ */
+import { beforeAll, beforeEach, describe, expect, it, vi } from "vitest";
+import * as OTPAuth from "otpauth";
+
+import { getPrismaClient, truncateAllTables } from "./setup";
+
+// hashToken (challenge ticket hashing) is fail-closed on a weak/absent key.
+process.env.API_TOKEN_HMAC_KEY ??=
+  "test-hmac-key-test-hmac-key-test-hmac-key-0123456789";
+
+vi.mock("@/lib/db-compat", () => ({
+  ensureDbCompatibility: vi.fn().mockResolvedValue(undefined),
+}));
+
+function codeAt(secretBase32: string, atMs: number): string {
+  const totp = new OTPAuth.TOTP({
+    issuer: "HealthLog",
+    label: "HealthLog",
+    algorithm: "SHA1",
+    digits: 6,
+    period: 30,
+    secret: OTPAuth.Secret.fromBase32(secretBase32),
+  });
+  return totp.generate({ timestamp: atMs });
+}
+
+let secret: string;
+let encrypt: (s: string) => string;
+
+beforeAll(async () => {
+  ({ encrypt } = await import("@/lib/crypto"));
+  const { generateTotpSecret } = await import("@/lib/auth/mfa/totp");
+  secret = generateTotpSecret();
+});
+
+beforeEach(async () => {
+  await truncateAllTables(getPrismaClient());
+});
+
+describe("MFA login flow (real Postgres)", () => {
+  it("TOTP verify persists the step and rejects a replay", async () => {
+    const { verifyMfaFactor } = await import("@/lib/auth/mfa/verify-factor");
+    const prisma = getPrismaClient();
+
+    const user = await prisma.user.create({
+      data: {
+        username: "totp-user",
+        email: "totp@example.test",
+        totpSecretEncrypted: encrypt(secret),
+        totpConfirmedAt: new Date(),
+      },
+    });
+
+    // verifyMfaFactor verifies against the real wall clock, so the code must
+    // be generated for "now".
+    const code = codeAt(secret, Date.now());
+
+    const first = await verifyMfaFactor(
+      { id: user.id, totpSecretEncrypted: encrypt(secret), totpLastStep: null },
+      "totp",
+      code,
+    );
+    expect(first.ok).toBe(true);
+
+    const afterFirst = await prisma.user.findUnique({
+      where: { id: user.id },
+      select: { totpLastStep: true },
+    });
+    expect(afterFirst?.totpLastStep).not.toBeNull();
+
+    // Replay the same code — the persisted step now floors it out.
+    const replay = await verifyMfaFactor(
+      {
+        id: user.id,
+        totpSecretEncrypted: encrypt(secret),
+        totpLastStep: afterFirst?.totpLastStep ?? null,
+      },
+      "totp",
+      code,
+    );
+    expect(replay.ok).toBe(false);
+    expect(replay.replay).toBe(true);
+  });
+
+  it("challenge is single-use and burns at the attempt cap", async () => {
+    const {
+      createMfaChallenge,
+      loadActiveChallenge,
+      claimChallenge,
+      recordChallengeFailure,
+      MFA_CHALLENGE_ATTEMPT_CAP,
+    } = await import("@/lib/auth/mfa/challenge");
+    const prisma = getPrismaClient();
+
+    const user = await prisma.user.create({
+      data: { username: "ch-user", email: "ch@example.test" },
+    });
+
+    const { ticket } = await createMfaChallenge(user.id, "login");
+    const active = await loadActiveChallenge(ticket);
+    expect(active).not.toBeNull();
+
+    // Claim-once: first claim wins, second loses, ticket no longer loadable.
+    expect(await claimChallenge(active!.id)).toBe(true);
+    expect(await claimChallenge(active!.id)).toBe(false);
+    expect(await loadActiveChallenge(ticket)).toBeNull();
+
+    // Attempt cap burns a fresh ticket.
+    const second = await createMfaChallenge(user.id, "login");
+    const row = await loadActiveChallenge(second.ticket);
+    let exhausted = false;
+    for (let i = 0; i < MFA_CHALLENGE_ATTEMPT_CAP; i++) {
+      ({ exhausted } = await recordChallengeFailure(row!.id));
+    }
+    expect(exhausted).toBe(true);
+    expect(await loadActiveChallenge(second.ticket)).toBeNull();
+  });
+
+  it("recovery code is one-time-use and regeneration invalidates the set", async () => {
+    const {
+      generateRecoveryCodes,
+      persistRecoveryCodes,
+      verifyAndConsumeRecoveryCode,
+      countRemainingRecoveryCodes,
+      regenerateRecoveryCodes,
+    } = await import("@/lib/auth/mfa/recovery-codes");
+    const prisma = getPrismaClient();
+
+    const user = await prisma.user.create({
+      data: { username: "rec-user", email: "rec@example.test" },
+    });
+
+    const codes = generateRecoveryCodes();
+    await persistRecoveryCodes(prisma, user.id, codes);
+    expect(await countRemainingRecoveryCodes(user.id)).toBe(codes.length);
+
+    // First use succeeds, second use of the same code fails.
+    expect(await verifyAndConsumeRecoveryCode(user.id, codes[0])).toBe(true);
+    expect(await verifyAndConsumeRecoveryCode(user.id, codes[0])).toBe(false);
+    expect(await countRemainingRecoveryCodes(user.id)).toBe(codes.length - 1);
+
+    // Regeneration drops every prior code (including the one not yet used).
+    const fresh = await regenerateRecoveryCodes(user.id);
+    expect(await countRemainingRecoveryCodes(user.id)).toBe(fresh.length);
+    expect(await verifyAndConsumeRecoveryCode(user.id, codes[1])).toBe(false);
+    expect(await verifyAndConsumeRecoveryCode(user.id, fresh[0])).toBe(true);
+  });
+});