From 15f729ffea2cec818f591e4e1d523f94fce38228 Mon Sep 17 00:00:00 2001
From: Lemon-miaow <admin@lemonmiaow.xyz>
Date: Thu, 24 Sep 2026 15:37:01 +0800
Subject: [PATCH] =?UTF-8?q?fix(auth):=20=E9=82=AE=E7=AE=B1=E9=AA=8C?=
 =?UTF-8?q?=E8=AF=81=E7=A0=81=E6=8C=89=E8=B4=A6=E5=8F=B7=E7=B4=AF=E8=AE=A1?=
 =?UTF-8?q?=E9=94=99=E8=AF=AF=E6=AC=A1=E6=95=B0=E5=B0=81=E9=A1=B6=E5=B9=B6?=
 =?UTF-8?q?=E9=80=9A=E7=9F=A5?=
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 8bit

---
 docs/openapi.yaml                             |  47 +++--
 internal/api/api_test.go                      |  46 ++++-
 internal/api/errors.go                        |  20 ++
 internal/api/handlers_account_migrate.go      |  12 ++
 internal/api/handlers_auth_email.go           |  17 +-
 internal/api/handlers_email_otp.go            |  22 +++
 internal/api/handlers_op_login.go             |  12 +-
 internal/api/otp_lock.go                      | 105 ++++++++++
 internal/api/otp_lock_test.go                 | 183 ++++++++++++++++++
 internal/api/pgrepo.go                        | 101 ++++++++--
 internal/api/repo.go                          |  15 +-
 internal/metrics/metrics.go                   |  10 +
 internal/pgint/pgint_test.go                  |  93 +++++++++
 .../migrations/0022_otp_failure_budget.sql    |  14 ++
 panel/src/i18n/resources/en-US/errors.json    |   1 +
 panel/src/i18n/resources/zh-CN/errors.json    |   1 +
 panel/src/lib/api.ts                          |   2 +
 17 files changed, 664 insertions(+), 37 deletions(-)
 create mode 100644 internal/api/otp_lock.go
 create mode 100644 internal/api/otp_lock_test.go
 create mode 100644 internal/store/migrations/0022_otp_failure_budget.sql

diff --git a/docs/openapi.yaml b/docs/openapi.yaml
index 371b856..f53d27d 100644
--- a/docs/openapi.yaml
+++ b/docs/openapi.yaml
@@ -2209,7 +2209,9 @@ paths:
         purpose. An address with no account returns the SAME 202 with no code minted,
         and the per-recipient cooldown is kept on that path too, so probing reveals
         nothing (existence is learnt only at the sanctioned /auth/options oracle).
-        Gated on local_auth_enabled.
+        An account that spent its daily wrong-code budget (10 per 24h, across every
+        code) also gets the same 202 and no mail until the window ends. Gated on
+        local_auth_enabled.
       x-felis-face: [external]
       x-felis-tier: public
       security: []
@@ -2268,7 +2270,10 @@ paths:
         under the login purpose, and on success mints a host-only felis_session. An
         unknown address, a wrong or expired code, and an attempt-exhausted code all
         return the IDENTICAL 400 invalid_code, so the door is not an existence or
-        lockout oracle. Staff are refused (403) — but only AFTER a valid code is
+        lockout oracle. The 10th wrong code in 24h locks the door for that account
+        until the window ends (the right code then also reads as invalid_code); the
+        owner is told by mail once, and the lock is audited as auth.otp.locked.
+        Staff are refused (403) — but only AFTER a valid code is
         redeemed, so only the account owner can ever reach that refusal.
       x-felis-face: [external]
       x-felis-tier: public
@@ -2324,7 +2329,8 @@ paths:
         staff address, opens an op_login request, and mails a one-time code under the
         op_login purpose, returning the request handle the browser polls. A non-staff
         or unknown address gets the SAME 202 with a random, non-persisted handle and no
-        mail, so this never becomes a staff-enumeration oracle. Gated on
+        mail, so this never becomes a staff-enumeration oracle. A staff account that
+        spent its daily wrong-code budget gets the same neutral 202. Gated on
         local_auth_enabled.
       x-felis-face: [external]
       x-felis-tier: public
@@ -2415,7 +2421,7 @@ paths:
         Public, pre-session final leg: mints a host-only staff session only when BOTH
         factors have landed — the request is approved-and-live AND the mailed code
         verifies. Every failure (unknown handle, not-yet-approved, wrong or locked code,
-        lost race) collapses into one uniform 400 op_login_invalid, so a code-less
+        an account past its daily wrong-code budget, lost race) collapses into one uniform 400 op_login_invalid, so a code-less
         caller learns nothing. Admin is re-asserted before the session is issued.
       x-felis-face: [external]
       x-felis-tier: public
@@ -3768,6 +3774,14 @@ paths:
               schema: { $ref: '#/components/schemas/Error' }
         '401':
           $ref: '#/components/responses/Unauthorized'
+        '429':
+          description: >-
+            Resend requested before the cooldown elapsed (otp_resend_cooldown); or the
+            account spent its daily wrong-code budget (otp_account_locked, with
+            Retry-After).
+          content:
+            application/json:
+              schema: { $ref: '#/components/schemas/Error' }
         '502':
           $ref: '#/components/responses/MailUndeliverable'
 
@@ -3779,8 +3793,10 @@ paths:
       description: >
         Consumes a previously delivered code for the authenticated principal. On
         success the user's email is written and email_verified is set true. Too many
-        incorrect attempts lock the code (429); an unknown, expired, consumed, or
-        mismatched code is a 400.
+        incorrect attempts lock the code (429 otp_locked); 10 wrong codes in 24h,
+        counted across every code, lock the account's email-code door until the
+        window ends (429 otp_account_locked with Retry-After). An unknown, expired,
+        consumed, or mismatched code is a 400.
       x-felis-face: [external]
       x-felis-tier: app
       security: [{ accessJWT: [] }]
@@ -3812,7 +3828,9 @@ paths:
         '401':
           $ref: '#/components/responses/Unauthorized'
         '429':
-          description: Too many incorrect attempts; the code is locked.
+          description: >-
+            Too many incorrect attempts on this code (otp_locked), or the account's
+            daily wrong-code budget is spent (otp_account_locked, with Retry-After).
           content:
             application/json:
               schema: { $ref: '#/components/schemas/Error' }
@@ -4070,7 +4088,10 @@ paths:
             application/json:
               schema: { $ref: '#/components/schemas/Error' }
         '429':
-          description: Resend requested before the cooldown elapsed.
+          description: >-
+            Resend requested before the cooldown elapsed (otp_resend_cooldown), or the
+            account's daily wrong-code budget is spent (otp_account_locked, with
+            Retry-After).
           content:
             application/json:
               schema: { $ref: '#/components/schemas/Error' }
@@ -4085,8 +4106,9 @@ paths:
       description: >
         Consumes the fresh migrate-purpose email code for the caller's initiated
         migration and advances it to confirmed with confirm_factor email_otp. Too many
-        wrong attempts lock the code (429 otp_locked); an unknown, expired, consumed, or
-        mismatched code is a 400 invalid_code.
+        wrong attempts lock the code (429 otp_locked), and 10 wrong codes in 24h lock
+        the account's email-code door (429 otp_account_locked with Retry-After); an
+        unknown, expired, consumed, or mismatched code is a 400 invalid_code.
       x-felis-face: [external]
       x-felis-tier: app
       security: [{ accessJWT: [] }]
@@ -4127,7 +4149,10 @@ paths:
             application/json:
               schema: { $ref: '#/components/schemas/Error' }
         '429':
-          description: The code is locked after too many wrong attempts (otp_locked).
+          description: >-
+            The code is locked after too many wrong attempts (otp_locked), or the
+            account's daily wrong-code budget is spent (otp_account_locked, with
+            Retry-After).
           content:
             application/json:
               schema: { $ref: '#/components/schemas/Error' }
diff --git a/internal/api/api_test.go b/internal/api/api_test.go
index f73c166..c0531ff 100644
--- a/internal/api/api_test.go
+++ b/internal/api/api_test.go
@@ -74,6 +74,8 @@ type fakeRepo struct {
 	// player email OTPs (spec §B2). Keyed by row id; the verify path scans for the
 	// newest live (user, purpose) just as the PG query does.
 	otps map[string]*fakeEmailOTP
+	// otpBudget mirrors otp_failure_windows, keyed user|purpose.
+	otpBudget map[string]*fakeOTPBudget
 	// op-login requests (spec §B op-login). opLogins mirrors op_login_requests keyed
 	// by id; the in-game approve/finish paths mutate status/consumed in place, and
 	// tests plant rows directly to drive the status/finish/pending-list paths.
@@ -151,6 +153,37 @@ type fakeDataHold struct {
 	expiresAt time.Time
 }
 
+// fakeOTPBudget mirrors an otp_failure_windows row.
+type fakeOTPBudget struct {
+	windowStart time.Time
+	failures    int
+}
+
+// OTPLockedUntil mirrors PGRepo.OTPLockedUntil through the shared otpLockEnd rule.
+func (f *fakeRepo) OTPLockedUntil(_ context.Context, userID, purpose string, now time.Time) (time.Time, error) {
+	b := f.otpBudget[userID+"|"+purpose]
+	if b == nil {
+		return time.Time{}, nil
+	}
+	return otpLockEnd(b.windowStart, b.failures, now), nil
+}
+
+// chargeOTP mirrors chargeOTPMismatch: one wrong guess on the code and the budget.
+func (f *fakeRepo) chargeOTP(live *fakeEmailOTP, now time.Time) error {
+	live.attempts++
+	key := live.userID + "|" + live.purpose
+	b := f.otpBudget[key]
+	if b == nil || !b.windowStart.Add(otpFailureWindow).After(now) {
+		b = &fakeOTPBudget{windowStart: now}
+		f.otpBudget[key] = b
+	}
+	b.failures++
+	if b.failures == otpFailureBudget {
+		return &OTPAccountLockedError{Until: b.windowStart.Add(otpFailureWindow), JustLocked: true}
+	}
+	return ErrOTPInvalid
+}
+
 // fakeEmailOTP mirrors an email_otps row: only the code hash is held (never the
 // digits), attempts caps brute force, consumed marks single-use, and createdAt
 // orders the newest-live lookup.
@@ -227,6 +260,7 @@ func newFakeRepo() *fakeRepo {
 		sessions:          map[string]*fakeSession{},
 		settings:          map[string][]byte{},
 		otps:              map[string]*fakeEmailOTP{},
+		otpBudget:         map[string]*fakeOTPBudget{},
 		opLogins:          map[string]*fakeOpLogin{},
 		setupTokens:       map[string]fakeSetupToken{},
 		blacklist:         map[string]bool{},
@@ -373,12 +407,14 @@ func (f *fakeRepo) VerifyEmailOTP(_ context.Context, userID, purpose, codeHash s
 	if !live.expiresAt.After(now) {
 		return "", ErrOTPInvalid
 	}
+	if until, _ := f.OTPLockedUntil(context.Background(), userID, purpose, now); !until.IsZero() {
+		return "", &OTPAccountLockedError{Until: until}
+	}
 	if live.attempts >= otpMaxAttempts {
 		return "", ErrOTPLocked
 	}
 	if live.codeHash != codeHash {
-		live.attempts++ // a typo costs an attempt but does not consume the code
-		return "", ErrOTPInvalid
+		return "", f.chargeOTP(live, now) // a typo costs an attempt but does not consume the code
 	}
 	// A DIFFERENT verified holder of the same address → ErrEmailTaken, code left
 	// live — mirrors PGRepo's guard + the users_verified_email_unique index.
@@ -1319,12 +1355,14 @@ func (f *fakeRepo) ConsumeLoginEmailOTP(_ context.Context, userID, purpose, code
 	if live == nil || !live.expiresAt.After(now) {
 		return ErrOTPInvalid
 	}
+	if until, _ := f.OTPLockedUntil(context.Background(), userID, purpose, now); !until.IsZero() {
+		return &OTPAccountLockedError{Until: until}
+	}
 	if live.attempts >= otpMaxAttempts {
 		return ErrOTPLocked
 	}
 	if live.codeHash != codeHash {
-		live.attempts++ // a typo costs an attempt but does not consume the code
-		return ErrOTPInvalid
+		return f.chargeOTP(live, now) // a typo costs an attempt but does not consume the code
 	}
 	live.consumed = true
 	return nil
diff --git a/internal/api/errors.go b/internal/api/errors.go
index 5fa34a9..9dea2ed 100644
--- a/internal/api/errors.go
+++ b/internal/api/errors.go
@@ -6,6 +6,7 @@ import (
 	"fmt"
 	"log"
 	"net/http"
+	"time"
 )
 
 // Sentinel errors the repository and cluster layers return so handlers can map
@@ -44,6 +45,11 @@ var (
 	// can answer 429 (back off / request a new code) rather than inviting another
 	// guess against a code that will never accept one.
 	ErrOTPLocked = errors.New("email code locked: too many attempts")
+	// ErrOTPAccountLocked means the (user, purpose) has spent its wrong-code budget
+	// for the current window (otpFailureBudget): every code for that door is refused,
+	// the right one included, until the window ends. The repo returns it as an
+	// *OTPAccountLockedError carrying the end of the lock.
+	ErrOTPAccountLocked = errors.New("email codes locked for this account: too many wrong codes")
 	// ErrPasskeyChallengeInvalid means a passkey enrollment ceremony cannot be
 	// finished: there is no live (unconsumed, unexpired) challenge for the caller and
 	// purpose (Phase 6 WebAuthn bind). Like ErrOTPInvalid it is a client error — the
@@ -102,6 +108,20 @@ func (e *MaintenanceBusyError) Error() string {
 
 func (e *MaintenanceBusyError) Is(target error) bool { return target == ErrMaintenanceInProgress }
 
+// OTPAccountLockedError is ErrOTPAccountLocked with its detail. JustLocked is set
+// only on the wrong guess that spent the budget, so the handler notifies and
+// audits the lock exactly once.
+type OTPAccountLockedError struct {
+	Until      time.Time
+	JustLocked bool
+}
+
+func (e *OTPAccountLockedError) Error() string {
+	return ErrOTPAccountLocked.Error() + " until " + e.Until.UTC().Format(time.RFC3339)
+}
+
+func (e *OTPAccountLockedError) Is(target error) bool { return target == ErrOTPAccountLocked }
+
 // apiError is a handler-level error carrying an HTTP status and a stable,
 // machine-readable code. The error envelope matches the platform convention:
 //
diff --git a/internal/api/handlers_account_migrate.go b/internal/api/handlers_account_migrate.go
index 4dd3a1e..2e490cd 100644
--- a/internal/api/handlers_account_migrate.go
+++ b/internal/api/handlers_account_migrate.go
@@ -206,6 +206,13 @@ func (a *API) handleMigrateConfirmOTPStart(w http.ResponseWriter, r *http.Reques
 	}
 	// Per-recipient cooldown, namespaced apart from the other OTP doors so they never
 	// perturb each other's throttle.
+	if until, err := a.Repo.OTPLockedUntil(r.Context(), p.UserID, otpPurposeMigrate, a.now()); err != nil {
+		writeError(w, r, err)
+		return
+	} else if !until.IsZero() {
+		writeOTPAccountLocked(w, r, until, a.now())
+		return
+	}
 	emailKey := "migrate:confirm:" + strings.ToLower(p.Email)
 	lim := a.otpLimiter()
 	emailAt, ok := lim.reserve(emailKey, otpResendCooldown)
@@ -267,7 +274,12 @@ func (a *API) handleMigrateConfirmOTPVerify(w http.ResponseWriter, r *http.Reque
 	if _, ok := a.requireInitiatedMigration(w, r, p.UserID); !ok {
 		return
 	}
+	var lock *OTPAccountLockedError
 	switch err := a.Repo.ConsumeLoginEmailOTP(r.Context(), p.UserID, otpPurposeMigrate, otpCodeHash(code), a.now()); {
+	case errors.As(err, &lock):
+		a.noteOTPLock(r, err, p.UserID, otpPurposeMigrate)
+		writeOTPAccountLocked(w, r, lock.Until, a.now())
+		return
 	case errors.Is(err, ErrOTPLocked):
 		writeError(w, r, newError(http.StatusTooManyRequests, "otp_locked",
 			"too many incorrect attempts; request a new code"))
diff --git a/internal/api/handlers_auth_email.go b/internal/api/handlers_auth_email.go
index ae6339a..6e75964 100644
--- a/internal/api/handlers_auth_email.go
+++ b/internal/api/handlers_auth_email.go
@@ -126,6 +126,19 @@ func (a *API) handleLoginEmailStart(w http.ResponseWriter, r *http.Request) {
 		return
 	}
 
+	// A locked door (wrong-code budget spent) gets the same neutral 202 and no
+	// mail: the owner was told by the lock notice, and a distinct answer here
+	// would tell a prober the address has an account.
+	switch until, err := a.Repo.OTPLockedUntil(r.Context(), u.ID, otpPurposeLogin, a.now()); {
+	case err != nil:
+		writeError(w, r, err)
+		return
+	case !until.IsZero():
+		committed = true
+		writeJSON(w, http.StatusAccepted, map[string]any{"sent": true, "expires_at": expiresAt.UTC()})
+		return
+	}
+
 	code, err := newEmailOTP()
 	if err != nil {
 		writeError(w, r, err)
@@ -220,7 +233,9 @@ func (a *API) handleLoginEmailVerify(w http.ResponseWriter, r *http.Request) {
 	// verified; touching the row here would let a stale OTP-snapshot address overwrite
 	// the live one and could 500 a correct code on a spurious collision.
 	switch err := a.Repo.ConsumeLoginEmailOTP(r.Context(), u.ID, otpPurposeLogin, otpCodeHash(code), a.now()); {
-	case errors.Is(err, ErrOTPInvalid), errors.Is(err, ErrOTPLocked):
+	case errors.Is(err, ErrOTPInvalid), errors.Is(err, ErrOTPLocked), errors.Is(err, ErrOTPAccountLocked):
+		// The account lock answers the same way; its owner hears about it by mail.
+		a.noteOTPLock(r, err, u.ID, otpPurposeLogin)
 		// Both a wrong/expired code and an attempt-exhausted one return the SAME 400
 		// invalid_code, byte-identical to the unknown-account branch above. Surfacing
 		// otp_locked as a distinct 429 (as the authenticated onboarding door does) would
diff --git a/internal/api/handlers_email_otp.go b/internal/api/handlers_email_otp.go
index dfc2fbd..a9fc1b6 100644
--- a/internal/api/handlers_email_otp.go
+++ b/internal/api/handlers_email_otp.go
@@ -47,6 +47,14 @@ const (
 	// keys (principal and recipient) so neither one account fanning out across many
 	// addresses, nor many accounts converging on one address, can flood a mailbox.
 	otpResendCooldown = 60 * time.Second
+	// otpFailureBudget caps wrong codes per (user, purpose) inside otpFailureWindow,
+	// across every code minted in it. The per-code cap alone resets on each resend,
+	// and the public login door can mint a code a minute, so without this an
+	// attacker gets ~7,200 guesses a day at one account. Ten a day puts a blind hit
+	// at 1e-5 per day; a person who mistypes that often can wait out the window or
+	// use a passkey.
+	otpFailureBudget = 10
+	otpFailureWindow = 24 * time.Hour
 )
 
 // OTPMailer delivers a one-time code to an email address. It is a seam, not a
@@ -129,6 +137,15 @@ func (a *API) handleEmailOTPStart(w http.ResponseWriter, r *http.Request) {
 	// can't sidestep the per-mailbox cap. If any later step fails the deferred rollback
 	// frees both windows, so a failed mint or delivery never consumes the cooldown —
 	// the same property the old record-after-send gave, now race-free.
+	// A spent wrong-code budget locks the door; mailing another code into it
+	// would only spend a send.
+	if until, err := a.Repo.OTPLockedUntil(r.Context(), p.UserID, otpPurposeOnboard, a.now()); err != nil {
+		writeError(w, r, err)
+		return
+	} else if !until.IsZero() {
+		writeOTPAccountLocked(w, r, until, a.now())
+		return
+	}
 	userKey, emailKey := "user:"+p.UserID, "email:"+strings.ToLower(email)
 	lim := a.otpLimiter()
 	userAt, ok := lim.reserve(userKey, otpResendCooldown)
@@ -205,7 +222,12 @@ func (a *API) handleEmailOTPVerify(w http.ResponseWriter, r *http.Request) {
 		return
 	}
 	email, err := a.Repo.VerifyEmailOTP(r.Context(), p.UserID, otpPurposeOnboard, otpCodeHash(code), a.now())
+	var lock *OTPAccountLockedError
 	switch {
+	case errors.As(err, &lock):
+		a.noteOTPLock(r, err, p.UserID, otpPurposeOnboard)
+		writeOTPAccountLocked(w, r, lock.Until, a.now())
+		return
 	case errors.Is(err, ErrOTPLocked):
 		writeError(w, r, newError(http.StatusTooManyRequests, "otp_locked",
 			"too many incorrect attempts; request a new code"))
diff --git a/internal/api/handlers_op_login.go b/internal/api/handlers_op_login.go
index dc872e0..2e840ba 100644
--- a/internal/api/handlers_op_login.go
+++ b/internal/api/handlers_op_login.go
@@ -144,6 +144,15 @@ func (a *API) handleOpLoginStart(w http.ResponseWriter, r *http.Request) {
 		neutral()
 		return
 	}
+	// A locked door (wrong-code budget spent) is neutral too: no request, no mail.
+	switch until, err := a.Repo.OTPLockedUntil(r.Context(), u.ID, otpPurposeOpLogin, a.now()); {
+	case err != nil:
+		writeError(w, r, err)
+		return
+	case !until.IsZero():
+		neutral()
+		return
+	}
 
 	id, err := newOTPID()
 	if err != nil {
@@ -272,7 +281,8 @@ func (a *API) handleOpLoginFinish(w http.ResponseWriter, r *http.Request) {
 	// attempt without minting anything and returns the uniform failure — the code, not
 	// the request, is the problem, and the request stays approved for a retry.
 	switch err := a.Repo.ConsumeLoginEmailOTP(r.Context(), loginReq.UserID, otpPurposeOpLogin, otpCodeHash(code), now); {
-	case errors.Is(err, ErrOTPInvalid), errors.Is(err, ErrOTPLocked):
+	case errors.Is(err, ErrOTPInvalid), errors.Is(err, ErrOTPLocked), errors.Is(err, ErrOTPAccountLocked):
+		a.noteOTPLock(r, err, loginReq.UserID, otpPurposeOpLogin)
 		writeError(w, r, invalid)
 		return
 	case err != nil:
diff --git a/internal/api/otp_lock.go b/internal/api/otp_lock.go
new file mode 100644
index 0000000..d09e8e0
--- /dev/null
+++ b/internal/api/otp_lock.go
@@ -0,0 +1,105 @@
+package api
+
+import (
+	"context"
+	"encoding/json"
+	"errors"
+	"fmt"
+	"log"
+	"net/http"
+	"strconv"
+	"time"
+
+	"felis.lolicon.best/internal/metrics"
+)
+
+// The account-level wrong-code budget (otpFailureBudget per otpFailureWindow)
+// is enforced in the repo; this file is what the doors do with it. The two
+// pre-session doors (email login, op-login) answer a locked account exactly
+// like a wrong code, so they never become an existence oracle; the owner
+// learns about the lock from a notice mail instead. The signed-in doors
+// (onboarding, migration step-up) answer 429 otp_account_locked with the time
+// the lock ends.
+
+// noticeSender is the optional half of Mailer that sends a free-form notice;
+// internal/mail.SMTP implements it (the reaper uses the same method).
+type noticeSender interface {
+	SendNotice(ctx context.Context, email, subject, body string) error
+}
+
+// otpDoorName names each purpose in the lock notice, in both languages.
+var otpDoorName = map[string][2]string{
+	otpPurposeLogin:   {"邮箱验证码登录", "email-code sign-in"},
+	otpPurposeOpLogin: {"管理员登录", "staff sign-in"},
+}
+
+// writeOTPAccountLocked answers a signed-in door whose budget is spent.
+func writeOTPAccountLocked(w http.ResponseWriter, r *http.Request, until, now time.Time) {
+	secs := int64(until.Sub(now).Round(time.Second) / time.Second)
+	if secs < 1 {
+		secs = 1
+	}
+	w.Header().Set("Retry-After", strconv.FormatInt(secs, 10))
+	writeError(w, r, newError(http.StatusTooManyRequests, "otp_account_locked",
+		"too many wrong codes on this account; email codes work again after %s",
+		until.UTC().Format(time.RFC3339)))
+}
+
+// noteOTPLock handles a redeem that met the account lock. Only the guess that
+// spent the budget (JustLocked) does anything: count, audit, log, and for the
+// pre-session doors mail the account so its owner learns why the right code
+// stopped working. Everything here is best effort; the lock already holds.
+func (a *API) noteOTPLock(r *http.Request, err error, userID, purpose string) {
+	var lock *OTPAccountLockedError
+	if !errors.As(err, &lock) || !lock.JustLocked {
+		return
+	}
+	metrics.OTPLockoutsTotal.WithLabelValues(purpose).Inc()
+	log.Printf("auth: %s codes for user %s locked until %s after %d wrong codes (request_id=%s)",
+		purpose, userID, lock.Until.UTC().Format(time.RFC3339), otpFailureBudget, requestIDFromContext(r.Context()))
+
+	ctx := r.Context()
+	actor := userID
+	u, uerr := a.Repo.UserByID(ctx, userID)
+	if uerr == nil && u.Username != "" {
+		actor = u.Username
+	}
+	payload, _ := json.Marshal(map[string]any{
+		"user_id": userID, "purpose": purpose, "until": lock.Until.UTC(), "failures": otpFailureBudget,
+	})
+	if aerr := a.Repo.Audit(ctx, AuditEntry{
+		Actor: actor, Source: "external", Action: "auth.otp.locked",
+		RequestID: requestIDFromContext(ctx), Payload: payload,
+	}); aerr != nil {
+		log.Printf("auth: audit of otp lock for user %s failed: %v", userID, aerr)
+	}
+
+	door, notify := otpDoorName[purpose]
+	if !notify || uerr != nil || u.Email == "" {
+		return
+	}
+	sender, ok := a.Mailer.(noticeSender)
+	if !ok {
+		log.Printf("auth: no notice mailer; user %s was not told their %s is locked", userID, purpose)
+		return
+	}
+	subject, body := otpLockNotice(door, lock.Until)
+	if err := sender.SendNotice(ctx, u.Email, subject, body); err != nil {
+		log.Printf("auth: otp lock notice to user %s failed: %v", userID, err)
+	}
+}
+
+// otpLockNotice renders the bilingual lock notice.
+func otpLockNotice(door [2]string, until time.Time) (subject, body string) {
+	at := until.UTC().Format("2006-01-02 15:04 MST")
+	subject = "Felis " + door[0] + "已暂停 · " + door[1] + " paused"
+	body = fmt.Sprintf(`Felis 在 24 小时内收到了 %[1]d 次错误的邮箱验证码，已暂停这个账户的%[2]s，%[3]s 自动恢复。
+如果不是你本人在尝试，说明有人在猜你的验证码。账户仍然安全：暂停期间任何验证码都无法登录。
+你仍然可以用已绑定的 Passkey 登录。
+
+Felis received %[1]d wrong email codes for this account within 24 hours and paused %[4]s until %[3]s.
+If this wasn't you, someone is guessing your code. Your account is safe: no code works while it is paused.
+You can still sign in with a passkey you have registered.
+`, otpFailureBudget, door[0], at, door[1])
+	return subject, body
+}
diff --git a/internal/api/otp_lock_test.go b/internal/api/otp_lock_test.go
new file mode 100644
index 0000000..f01944d
--- /dev/null
+++ b/internal/api/otp_lock_test.go
@@ -0,0 +1,183 @@
+package api
+
+import (
+	"context"
+	"net/http"
+	"strings"
+	"testing"
+	"time"
+)
+
+// The per-code attempt cap resets on every resend; these pin the account-level
+// budget that does not. The public login door must stay uniform (a locked
+// account reads like a wrong code and mails nothing), tell the owner by mail
+// once, and reopen when the window ends. The signed-in onboarding door answers
+// 429 with Retry-After instead.
+
+type noticeMailer struct {
+	captureMailer
+	notices []string // "to|subject|body"
+}
+
+func (m *noticeMailer) SendNotice(_ context.Context, email, subject, body string) error {
+	m.notices = append(m.notices, email+"|"+subject+"|"+body)
+	return nil
+}
+
+func TestLoginDoorLocksAfterDailyWrongCodeBudget(t *testing.T) {
+	api, repo, _ := seedLoginEmailAPI(t)
+	mailer := &noticeMailer{}
+	api.Mailer = mailer
+	clock := time.Unix(1_700_000_000, 0)
+	api.Now = func() time.Time { return clock }
+	eh := api.ExternalHandler()
+
+	start := func() {
+		t.Helper()
+		clock = clock.Add(otpResendCooldown + time.Second)
+		if w := do(eh, "POST", "/api/v1/auth/email/start", `{"email":"player@example.net"}`, jsonHeader); w.Code != http.StatusAccepted {
+			t.Fatalf("start = %d (%s)", w.Code, w.Body.String())
+		}
+	}
+	verify := func(code string) int {
+		t.Helper()
+		w := do(eh, "POST", "/api/v1/auth/email/verify", `{"email":"player@example.net","code":"`+code+`"}`, jsonHeader)
+		if w.Code != http.StatusOK {
+			if c, _ := errEnvelope(t, w); c != "invalid_code" {
+				t.Fatalf("verify answered %d %s; the login door must only ever say invalid_code", w.Code, c)
+			}
+		}
+		return w.Code
+	}
+
+	// Ten wrong codes over three sends; no single code reaches its own cap.
+	for i := 0; i < otpFailureBudget; i++ {
+		if i%4 == 0 {
+			start()
+		}
+		if code := verify("not-the-code"); code != http.StatusBadRequest {
+			t.Fatalf("wrong guess %d = %d", i+1, code)
+		}
+	}
+	sends := mailer.calls
+	liveCode := mailer.code
+
+	if len(mailer.notices) != 1 || !strings.HasPrefix(mailer.notices[0], "Player@Example.NET|") {
+		t.Fatalf("lock notices = %q, want one to the stored address", mailer.notices)
+	}
+	var lockAudits int
+	for _, a := range repo.audits {
+		if a.Action == "auth.otp.locked" {
+			lockAudits++
+			if a.Actor != "player" || !strings.Contains(string(a.Payload), `"purpose":"login_email"`) {
+				t.Fatalf("lock audit = %+v", a)
+			}
+		}
+	}
+	if lockAudits != 1 {
+		t.Fatalf("lock audits = %d, want 1", lockAudits)
+	}
+
+	// Locked: the right code fails like a wrong one, and a resend mails nothing.
+	if code := verify(liveCode); code != http.StatusBadRequest {
+		t.Fatalf("right code while locked = %d, want 400", code)
+	}
+	start()
+	if mailer.calls != sends {
+		t.Fatalf("a locked door mailed a code (%d sends, want %d)", mailer.calls, sends)
+	}
+	if len(mailer.notices) != 1 {
+		t.Fatalf("a standing lock re-sent the notice: %d", len(mailer.notices))
+	}
+
+	// The window ends: a fresh send and its code work again.
+	clock = clock.Add(otpFailureWindow)
+	start()
+	if mailer.calls != sends+1 {
+		t.Fatalf("no code mailed after the window (%d sends)", mailer.calls)
+	}
+	if code := verify(mailer.code); code != http.StatusOK {
+		t.Fatalf("right code after the window = %d, want 200", code)
+	}
+}
+
+func TestOnboardDoorLockAnswers429(t *testing.T) {
+	repo := newFakeRepo()
+	repo.staff["player"] = &StaffUser{ID: "u1", Username: "player", Email: "old@example.net"}
+	mailer := &noticeMailer{}
+	api := newTestAPI(repo, newFakeCluster())
+	api.External = staticExternal{p: &Principal{UserID: "u1", Email: "u1@example.net", Role: "user"}}
+	api.Mailer = mailer
+	clock := time.Unix(1_700_000_000, 0)
+	api.Now = func() time.Time { return clock }
+	eh := api.ExternalHandler()
+
+	var last int
+	for i := 0; i < otpFailureBudget; i++ {
+		if i%4 == 0 {
+			clock = clock.Add(otpResendCooldown + time.Second)
+			if w := do(eh, "POST", "/api/v1/account/email/start", `{"email":"player@example.net"}`, nil); w.Code != http.StatusAccepted {
+				t.Fatalf("start = %d (%s)", w.Code, w.Body.String())
+			}
+		}
+		w := do(eh, "POST", "/api/v1/account/email/verify", `{"code":"not-the-code"}`, nil)
+		last = w.Code
+		if i == otpFailureBudget-1 {
+			if c, _ := errEnvelope(t, w); w.Code != http.StatusTooManyRequests || c != "otp_account_locked" {
+				t.Fatalf("10th wrong code = %d %s, want 429 otp_account_locked", w.Code, c)
+			}
+			if w.Header().Get("Retry-After") == "" {
+				t.Fatal("locked answer carries no Retry-After")
+			}
+		}
+	}
+	if last != http.StatusTooManyRequests {
+		t.Fatalf("last = %d", last)
+	}
+	// The signed-in owner sees the 429; no notice mail is needed.
+	if len(mailer.notices) != 0 {
+		t.Fatalf("onboarding lock mailed a notice: %q", mailer.notices)
+	}
+	clock = clock.Add(otpResendCooldown + time.Second)
+	sends := mailer.calls
+	w := do(eh, "POST", "/api/v1/account/email/start", `{"email":"player@example.net"}`, nil)
+	if c, _ := errEnvelope(t, w); w.Code != http.StatusTooManyRequests || c != "otp_account_locked" || mailer.calls != sends {
+		t.Fatalf("start while locked = %d %s (sends %d→%d), want 429 and no mail", w.Code, c, sends, mailer.calls)
+	}
+}
+
+func TestOTPLockEnd(t *testing.T) {
+	t0 := time.Date(2026, 9, 24, 8, 0, 0, 0, time.UTC)
+	for _, tc := range []struct {
+		name     string
+		failures int
+		now      time.Time
+		locked   bool
+	}{
+		{"under budget", otpFailureBudget - 1, t0.Add(time.Hour), false},
+		{"budget spent", otpFailureBudget, t0.Add(time.Hour), true},
+		{"window just ended", otpFailureBudget, t0.Add(otpFailureWindow), false},
+	} {
+		got := otpLockEnd(t0, tc.failures, tc.now)
+		if got.IsZero() == tc.locked {
+			t.Errorf("%s: otpLockEnd = %v, locked want %v", tc.name, got, tc.locked)
+		}
+		if tc.locked && !got.Equal(t0.Add(otpFailureWindow)) {
+			t.Errorf("%s: lock ends %v, want window end", tc.name, got)
+		}
+	}
+}
+
+func TestOTPLockNoticeNamesDoorAndTime(t *testing.T) {
+	subject, body := otpLockNotice(otpDoorName[otpPurposeLogin], time.Date(2026, 9, 25, 8, 0, 0, 0, time.UTC))
+	for _, want := range []string{"邮箱验证码登录", "email-code sign-in"} {
+		if !strings.Contains(subject, want) {
+			t.Errorf("subject %q missing %q", subject, want)
+		}
+	}
+	for _, want := range []string{"2026-09-25 08:00 UTC", "Passkey", "passkey", "10"} {
+		if !strings.Contains(body, want) {
+			t.Errorf("body missing %q:\n%s", want, body)
+		}
+	}
+}
diff --git a/internal/api/pgrepo.go b/internal/api/pgrepo.go
index ffd706a..77e0467 100644
--- a/internal/api/pgrepo.go
+++ b/internal/api/pgrepo.go
@@ -820,18 +820,16 @@ func (p *PGRepo) VerifyEmailOTP(ctx context.Context, userID, purpose, codeHash s
 	if !expiresAt.After(now) {
 		return "", ErrOTPInvalid
 	}
+	if until, err := otpLockedUntil(ctx, tx, userID, purpose, now, true); err != nil {
+		return "", err
+	} else if !until.IsZero() {
+		return "", &OTPAccountLockedError{Until: until}
+	}
 	if attempts >= otpMaxAttempts {
 		return "", ErrOTPLocked
 	}
 	if storedHash != codeHash {
-		if _, err := tx.ExecContext(ctx,
-			`UPDATE email_otps SET attempts = attempts + 1 WHERE id = $1`, id); err != nil {
-			return "", fmt.Errorf("record otp attempt: %w", err)
-		}
-		if err := tx.Commit(); err != nil {
-			return "", err
-		}
-		return "", ErrOTPInvalid
+		return "", chargeOTPMismatch(ctx, tx, id, userID, purpose, now)
 	}
 
 	// A DIFFERENT account may not also prove this address: the pre-session login
@@ -2135,18 +2133,16 @@ func (p *PGRepo) ConsumeLoginEmailOTP(ctx context.Context, userID, purpose, code
 	if !expiresAt.After(now) {
 		return ErrOTPInvalid
 	}
+	if until, err := otpLockedUntil(ctx, tx, userID, purpose, now, true); err != nil {
+		return err
+	} else if !until.IsZero() {
+		return &OTPAccountLockedError{Until: until}
+	}
 	if attempts >= otpMaxAttempts {
 		return ErrOTPLocked
 	}
 	if storedHash != codeHash {
-		if _, err := tx.ExecContext(ctx,
-			`UPDATE email_otps SET attempts = attempts + 1 WHERE id = $1`, id); err != nil {
-			return fmt.Errorf("record otp attempt: %w", err)
-		}
-		if err := tx.Commit(); err != nil {
-			return err
-		}
-		return ErrOTPInvalid
+		return chargeOTPMismatch(ctx, tx, id, userID, purpose, now)
 	}
 
 	if _, err := tx.ExecContext(ctx,
@@ -2156,6 +2152,79 @@ func (p *PGRepo) ConsumeLoginEmailOTP(ctx context.Context, userID, purpose, code
 	return tx.Commit()
 }
 
+// OTPLockedUntil reads the (user, purpose) wrong-code lock for a start door.
+func (p *PGRepo) OTPLockedUntil(ctx context.Context, userID, purpose string, now time.Time) (time.Time, error) {
+	return otpLockedUntil(ctx, p.db, userID, purpose, now, false)
+}
+
+// otpQuerier is the read half shared by *sql.DB and *sql.Tx.
+type otpQuerier interface {
+	QueryRowContext(ctx context.Context, query string, args ...any) *sql.Row
+}
+
+// otpLockedUntil returns when the (user, purpose) lock ends, or zero when the
+// budget is not spent in the current window. forUpdate takes the row lock so a
+// redeem serialises its check with its own charge.
+func otpLockedUntil(ctx context.Context, q otpQuerier, userID, purpose string, now time.Time, forUpdate bool) (time.Time, error) {
+	query := `SELECT window_start, failures FROM otp_failure_windows WHERE user_id = $1 AND purpose = $2`
+	if forUpdate {
+		query += ` FOR UPDATE`
+	}
+	var (
+		start    time.Time
+		failures int
+	)
+	switch err := q.QueryRowContext(ctx, query, userID, purpose).Scan(&start, &failures); {
+	case errors.Is(err, sql.ErrNoRows):
+		return time.Time{}, nil
+	case err != nil:
+		return time.Time{}, fmt.Errorf("read otp failure budget: %w", err)
+	}
+	return otpLockEnd(start, failures, now), nil
+}
+
+// otpLockEnd is the lock rule on one budget row: spent inside a live window.
+func otpLockEnd(windowStart time.Time, failures int, now time.Time) time.Time {
+	end := windowStart.Add(otpFailureWindow)
+	if failures < otpFailureBudget || !end.After(now) {
+		return time.Time{}
+	}
+	return end
+}
+
+// chargeOTPMismatch records one wrong guess against the code and the account
+// budget, commits, and returns what the caller should answer: ErrOTPInvalid, or
+// the lock this guess just tripped. A window that has ended starts over at 1.
+func chargeOTPMismatch(ctx context.Context, tx *sql.Tx, codeID, userID, purpose string, now time.Time) error {
+	if _, err := tx.ExecContext(ctx,
+		`UPDATE email_otps SET attempts = attempts + 1 WHERE id = $1`, codeID); err != nil {
+		return fmt.Errorf("record otp attempt: %w", err)
+	}
+	var (
+		start    time.Time
+		failures int
+	)
+	if err := tx.QueryRowContext(ctx,
+		`INSERT INTO otp_failure_windows (user_id, purpose, window_start, failures)
+		 VALUES ($1, $2, $3, 1)
+		 ON CONFLICT (user_id, purpose) DO UPDATE SET
+		   failures = CASE WHEN otp_failure_windows.window_start + $4 * interval '1 second' <= $3
+		                   THEN 1 ELSE otp_failure_windows.failures + 1 END,
+		   window_start = CASE WHEN otp_failure_windows.window_start + $4 * interval '1 second' <= $3
+		                   THEN $3 ELSE otp_failure_windows.window_start END
+		 RETURNING window_start, failures`,
+		userID, purpose, now, int64(otpFailureWindow/time.Second)).Scan(&start, &failures); err != nil {
+		return fmt.Errorf("charge otp failure budget: %w", err)
+	}
+	if err := tx.Commit(); err != nil {
+		return err
+	}
+	if failures == otpFailureBudget {
+		return &OTPAccountLockedError{Until: start.Add(otpFailureWindow), JustLocked: true}
+	}
+	return ErrOTPInvalid
+}
+
 // ---- op.console staff login: in-game approval state machine (spec §B op-login) ----
 
 // CreateOpLoginRequest records a fresh pending op.console login attempt for a staff
diff --git a/internal/api/repo.go b/internal/api/repo.go
index 715b198..3a55a78 100644
--- a/internal/api/repo.go
+++ b/internal/api/repo.go
@@ -314,9 +314,10 @@ type Repo interface {
 	CreateEmailOTP(ctx context.Context, id, userID, email, codeHash, purpose string, expiresAt time.Time) error
 	// VerifyEmailOTP redeems the newest live code for (userID, purpose) against
 	// codeHash, atomically (spec §B2). No live code, an expired one, or a consumed
-	// one → ErrOTPInvalid; an exhausted attempt budget → ErrOTPLocked; a hash
-	// mismatch increments attempts and returns ErrOTPInvalid WITHOUT consuming the
-	// code (so a typo does not burn it). On a match the code is consumed and the
+	// one → ErrOTPInvalid; an exhausted attempt budget → ErrOTPLocked; a spent
+	// (user, purpose) wrong-code budget → *OTPAccountLockedError, even for the right
+	// code; a hash mismatch increments attempts, charges that budget, and returns
+	// ErrOTPInvalid WITHOUT consuming the code (so a typo does not burn it). On a match the code is consumed and the
 	// user row is flipped to email=<the proven address>, email_verified=true; the
 	// proven email is returned — unless a DIFFERENT account has already proven the
 	// same address, which is ErrEmailTaken with the code left unconsumed (the
@@ -343,8 +344,14 @@ type Repo interface {
 	// settled — re-proving control of a code this session must not re-touch the row.
 	// Returning only an error is deliberate: unlike onboarding, login has nothing to
 	// prove about the address, so there is no email to hand back. Errors are exactly
-	// ErrOTPInvalid / ErrOTPLocked (ErrEmailTaken is structurally impossible here).
+	// ErrOTPInvalid / ErrOTPLocked / *OTPAccountLockedError (ErrEmailTaken is
+	// structurally impossible here).
 	ConsumeLoginEmailOTP(ctx context.Context, userID, purpose, codeHash string, now time.Time) error
+	// OTPLockedUntil reports when the (userID, purpose) wrong-code lock ends, or the
+	// zero time when that door is open. Both redeem paths enforce the lock
+	// themselves (returning *OTPAccountLockedError, and charging every mismatch to
+	// the budget); the start doors read it so a locked door mails no code.
+	OTPLockedUntil(ctx context.Context, userID, purpose string, now time.Time) (time.Time, error)
 
 	// ---- op.console staff login: in-game approval state machine (spec §B op-login) ----
 
diff --git a/internal/metrics/metrics.go b/internal/metrics/metrics.go
index 7db2331..0baf7fc 100644
--- a/internal/metrics/metrics.go
+++ b/internal/metrics/metrics.go
@@ -55,6 +55,15 @@ var (
 		Name:      "reaper_worlds_deleted_total",
 		Help:      "Total number of world volumes deleted by the reaper.",
 	})
+
+	// OTPLockoutsTotal counts accounts whose email-code door locked after the
+	// daily wrong-code budget was spent, by code purpose. Outside a person
+	// fumbling codes, a lockout means someone is guessing at that account.
+	OTPLockoutsTotal = prometheus.NewCounterVec(prometheus.CounterOpts{
+		Namespace: namespace,
+		Name:      "auth_otp_lockouts_total",
+		Help:      "Email-code doors locked after too many wrong codes, by purpose.",
+	}, []string{"purpose"})
 )
 
 // SyncServerGauge republishes felis_servers_total from a full snapshot of the
@@ -87,6 +96,7 @@ func Collectors() []prometheus.Collector {
 		StartDurationSeconds,
 		ImageBuildFailuresTotal,
 		ReaperWorldsDeletedTotal,
+		OTPLockoutsTotal,
 	}
 }
 
diff --git a/internal/pgint/pgint_test.go b/internal/pgint/pgint_test.go
index 1186ab5..38dc90d 100644
--- a/internal/pgint/pgint_test.go
+++ b/internal/pgint/pgint_test.go
@@ -324,6 +324,99 @@ func TestConsumeLoginEmailOTPContract(t *testing.T) {
 	}
 }
 
+// The account-level wrong-code budget must survive supersede: minting a fresh
+// code resets the per-code attempts, and the public login door can mint one a
+// minute, so only a counter outside email_otps bounds guessing per account.
+func TestOTPFailureBudgetContract(t *testing.T) {
+	ctx := context.Background()
+	u := newUser(t, "user", "otp-budget")
+	purpose := "login_email"
+	addr := "budget-" + suffix(t) + "@example.net"
+	start := mustNow().Truncate(time.Second)
+	mint := func(hash string, at time.Time) {
+		t.Helper()
+		if err := repo.CreateEmailOTP(ctx, "bud-"+suffix(t), u.ID, addr, hash, purpose, at.Add(5*time.Minute)); err != nil {
+			t.Fatalf("CreateEmailOTP: %v", err)
+		}
+	}
+
+	// Ten wrong guesses spread over three codes; the per-code cap (5) is never hit.
+	var tripped *api.OTPAccountLockedError
+	for i := 0; i < 10; i++ {
+		at := start.Add(time.Duration(i) * time.Minute)
+		if i%4 == 0 {
+			mint("h-good", at)
+		}
+		err := repo.ConsumeLoginEmailOTP(ctx, u.ID, purpose, "h-wrong", at)
+		if i < 9 {
+			if !errors.Is(err, api.ErrOTPInvalid) {
+				t.Fatalf("wrong guess %d = %v, want ErrOTPInvalid", i+1, err)
+			}
+			continue
+		}
+		if !errors.As(err, &tripped) || !tripped.JustLocked {
+			t.Fatalf("10th wrong guess = %v, want a fresh *OTPAccountLockedError", err)
+		}
+	}
+	if want := start.Add(24 * time.Hour); !tripped.Until.Equal(want) {
+		t.Fatalf("lock until %v, want %v (window opened by the first wrong guess)", tripped.Until, want)
+	}
+
+	// The right code on a live, barely-used code is refused while locked.
+	at := start.Add(10 * time.Minute)
+	var lock *api.OTPAccountLockedError
+	if err := repo.ConsumeLoginEmailOTP(ctx, u.ID, purpose, "h-good", at); !errors.As(err, &lock) || lock.JustLocked {
+		t.Fatalf("right code while locked = %v, want a standing *OTPAccountLockedError", err)
+	}
+	if until, err := repo.OTPLockedUntil(ctx, u.ID, purpose, at); err != nil || until.IsZero() {
+		t.Fatalf("OTPLockedUntil during lock = %v, %v", until, err)
+	}
+	// Other purposes of the same account are separate doors.
+	if until, err := repo.OTPLockedUntil(ctx, u.ID, "onboard_email", at); err != nil || !until.IsZero() {
+		t.Fatalf("onboard door locked too: %v, %v", until, err)
+	}
+
+	// After the window the door reopens and the count starts over.
+	later := start.Add(25 * time.Hour)
+	if until, err := repo.OTPLockedUntil(ctx, u.ID, purpose, later); err != nil || !until.IsZero() {
+		t.Fatalf("OTPLockedUntil after window = %v, %v", until, err)
+	}
+	mint("h-good", later)
+	if err := repo.ConsumeLoginEmailOTP(ctx, u.ID, purpose, "h-wrong", later); !errors.Is(err, api.ErrOTPInvalid) {
+		t.Fatalf("first wrong guess of a new window = %v, want ErrOTPInvalid", err)
+	}
+	var failures int
+	if err := db.QueryRowContext(ctx,
+		`SELECT failures FROM otp_failure_windows WHERE user_id = $1 AND purpose = $2`, u.ID, purpose).Scan(&failures); err != nil {
+		t.Fatalf("read budget row: %v", err)
+	}
+	if failures != 1 {
+		t.Fatalf("failures after window reset = %d, want 1", failures)
+	}
+	if err := repo.ConsumeLoginEmailOTP(ctx, u.ID, purpose, "h-good", later); err != nil {
+		t.Fatalf("right code after the window = %v, want nil", err)
+	}
+
+	// The onboarding primitive shares the rule.
+	onboard := "onboard_email"
+	for i := 0; i < 10; i++ {
+		at := start.Add(time.Duration(i) * time.Minute)
+		if i%4 == 0 {
+			if err := repo.CreateEmailOTP(ctx, "bud-on-"+suffix(t), u.ID, addr, "h-good", onboard, at.Add(5*time.Minute)); err != nil {
+				t.Fatalf("CreateEmailOTP onboard: %v", err)
+			}
+		}
+		_, err := repo.VerifyEmailOTP(ctx, u.ID, onboard, "h-wrong", at)
+		if i == 9 && !errors.Is(err, api.ErrOTPAccountLocked) {
+			t.Fatalf("10th wrong onboarding guess = %v, want ErrOTPAccountLocked", err)
+		}
+	}
+	if _, err := repo.VerifyEmailOTP(ctx, u.ID, onboard, "h-good", start.Add(10*time.Minute)); !errors.Is(err, api.ErrOTPAccountLocked) {
+		t.Fatalf("right onboarding code while locked = %v, want ErrOTPAccountLocked", err)
+	}
+	assertEmailProven(t, u.ID, "", false)
+}
+
 // ---- user admin (spec §7) -------------------------------------------------------
 
 // The claim gate must hold under concurrency (audit #4): two simultaneous claims
diff --git a/internal/store/migrations/0022_otp_failure_budget.sql b/internal/store/migrations/0022_otp_failure_budget.sql
new file mode 100644
index 0000000..d5a6abf
--- /dev/null
+++ b/internal/store/migrations/0022_otp_failure_budget.sql
@@ -0,0 +1,14 @@
+-- Account-level budget on wrong one-time codes. The per-code attempts cap
+-- (email_otps.attempts) resets whenever a new code is minted, and the public
+-- login door lets anyone mint one per minute, so on its own it allows about
+-- 7,200 guesses a day against one account. This row survives supersede: it
+-- counts every wrong code for a (user, purpose) inside a fixed window, and once
+-- the budget is spent that door refuses even the right code until the window
+-- ends (internal/api otpFailureBudget / otpFailureWindow).
+CREATE TABLE otp_failure_windows (
+  user_id      text        NOT NULL REFERENCES users(id) ON DELETE CASCADE,
+  purpose      text        NOT NULL,
+  window_start timestamptz NOT NULL,
+  failures     int         NOT NULL DEFAULT 0,
+  PRIMARY KEY (user_id, purpose)
+);
diff --git a/panel/src/i18n/resources/en-US/errors.json b/panel/src/i18n/resources/en-US/errors.json
index 96c4f08..8656c93 100644
--- a/panel/src/i18n/resources/en-US/errors.json
+++ b/panel/src/i18n/resources/en-US/errors.json
@@ -22,6 +22,7 @@
   "generic": "Something went wrong.",
   "otp_resend_cooldown": "Verification code requested too frequently, please try again later.",
   "otp_locked": "Too many incorrect attempts, please request a new verification code.",
+  "otp_account_locked": "Too many wrong codes in 24 hours — email codes for this account are paused. Try again later or use a passkey.",
   "passkey_challenge_invalid": "Passkey challenge is invalid or expired, please try again.",
   "invalid_attestation": "Could not verify this Passkey, please try again.",
   "passkey_already_bound": "This Passkey is already bound to another account.",
diff --git a/panel/src/i18n/resources/zh-CN/errors.json b/panel/src/i18n/resources/zh-CN/errors.json
index 19cc253..c1c8d47 100644
--- a/panel/src/i18n/resources/zh-CN/errors.json
+++ b/panel/src/i18n/resources/zh-CN/errors.json
@@ -22,6 +22,7 @@
   "generic": "出了点问题，请稍后重试。",
   "otp_resend_cooldown": "验证码发送频繁，请稍后再试。",
   "otp_locked": "验证码错误次数过多，请重新获取验证码。",
+  "otp_account_locked": "24 小时内验证码错误次数已达上限，此账号的邮箱验证码暂时停用，请稍后再试或改用 Passkey。",
   "passkey_challenge_invalid": "验证挑战无效或已过期，请重试。",
   "invalid_attestation": "无法验证此 Passkey，请重试。",
   "passkey_already_bound": "此 Passkey 已被其他账户绑定。",
diff --git a/panel/src/lib/api.ts b/panel/src/lib/api.ts
index cd0f91e..b057924 100644
--- a/panel/src/lib/api.ts
+++ b/panel/src/lib/api.ts
@@ -677,6 +677,8 @@ export function humanizeError(e: unknown): string {
       return t("otp_resend_cooldown");
     case "otp_locked":
       return t("otp_locked");
+    case "otp_account_locked":
+      return t("otp_account_locked");
     case "passkey_challenge_invalid":
       return t("passkey_challenge_invalid");
     case "invalid_attestation":