From b1f976fd7a5a221da03ab626503e6ffa161a69b0 Mon Sep 17 00:00:00 2001
From: smail <likb_blue@163.com>
Date: Tue, 6 Oct 2026 03:00:00 +0800
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---
 backend/services/verification/service.go      |  2 +-
 backend/services/verification/service_test.go | 27 +++++++++++++++++++
 2 files changed, 28 insertions(+), 1 deletion(-)

diff --git a/backend/services/verification/service.go b/backend/services/verification/service.go
index ebfdd25..5ed7bfe 100644
--- a/backend/services/verification/service.go
+++ b/backend/services/verification/service.go
@@ -70,7 +70,7 @@ func (s *Service) Issue(request IssueRequest, remoteIP string) (Challenge, error
 	allowed, release, limitErr := s.allow(request, remoteIP)
 	if limitErr != nil {
 		s.record(EventInput{Purpose: request.Purpose, Action: models.VerificationActionIssue, Outcome: models.VerificationOutcomeFailure, Account: request.Account, Email: request.Email, RemoteIP: remoteIP})
-		return Challenge{}, ErrServiceDown
+		return Challenge{}, fmt.Errorf("%w: %w", ErrServiceDown, limitErr)
 	}
 	if !allowed {
 		s.record(EventInput{Purpose: request.Purpose, Action: models.VerificationActionIssue, Outcome: models.VerificationOutcomeBlocked, Account: request.Account, Email: request.Email, RemoteIP: remoteIP})
diff --git a/backend/services/verification/service_test.go b/backend/services/verification/service_test.go
index deff19d..2030686 100644
--- a/backend/services/verification/service_test.go
+++ b/backend/services/verification/service_test.go
@@ -44,6 +44,33 @@ func TestServiceRequiresDelivery(t *testing.T) {
 	}
 }
 
+func TestServicePreservesRateLimitFailureWithoutSending(t *testing.T) {
+	store, err := NewStore(4)
+	if err != nil {
+		t.Fatal(err)
+	}
+	sent := false
+	service, err := NewService(store, func(_ Challenge, _ string) error {
+		sent = true
+		return nil
+	}, nil)
+	if err != nil {
+		t.Fatal(err)
+	}
+	service.SetRateLimitStore(&PersistentRateLimiter{})
+	_, err = service.Issue(IssueRequest{
+		Purpose: PurposeExternalEmailBind,
+		Account: "user",
+		Email:   "user@example.com",
+	}, "192.0.2.10")
+	if !errors.Is(err, ErrServiceDown) || !errors.Is(err, ErrRateLimitStoreUnavailable) {
+		t.Fatalf("error chain lost: %v", err)
+	}
+	if sent {
+		t.Fatal("delivery ran after rate limit storage failed")
+	}
+}
+
 func TestServiceAppliesIndependentAccountEmailAndIPLimits(t *testing.T) {
 	store, err := NewStore(64)
 	if err != nil {