diff --git a/backend/go.mod b/backend/go.mod
index 66b6cc25b5..12ff846027 100644
--- a/backend/go.mod
+++ b/backend/go.mod
@@ -54,6 +54,7 @@ require (
 	github.com/Azure/go-ansiterm v0.0.0-20210617225240-d185dfc1b5a1 // indirect
 	github.com/Microsoft/go-winio v0.6.2 // indirect
 	github.com/agext/levenshtein v1.2.3 // indirect
+	github.com/alicebob/miniredis/v2 v2.37.0 // indirect
 	github.com/apparentlymart/go-textseg/v15 v15.0.0 // indirect
 	github.com/aws/aws-sdk-go-v2/aws/protocol/eventstream v1.7.5 // indirect
 	github.com/aws/aws-sdk-go-v2/feature/ec2/imds v1.18.18 // indirect
@@ -158,6 +159,7 @@ require (
 	github.com/tklauser/numcpus v0.6.1 // indirect
 	github.com/twitchyliquid64/golang-asm v0.15.1 // indirect
 	github.com/ugorji/go/codec v1.2.11 // indirect
+	github.com/yuin/gopher-lua v1.1.1 // indirect
 	github.com/yusufpapurcu/wmi v1.2.4 // indirect
 	github.com/zclconf/go-cty v1.14.4 // indirect
 	github.com/zclconf/go-cty-yaml v1.1.0 // indirect
diff --git a/backend/go.sum b/backend/go.sum
index 9312af63e5..0502b30144 100644
--- a/backend/go.sum
+++ b/backend/go.sum
@@ -16,6 +16,8 @@ github.com/agext/levenshtein v1.2.3 h1:YB2fHEn0UJagG8T1rrWknE3ZQzWM06O8AMAatNn7l
 github.com/agext/levenshtein v1.2.3/go.mod h1:JEDfjyjHDjOF/1e4FlBE/PkbqA9OfWu2ki2W0IB5558=
 github.com/agiledragon/gomonkey v2.0.2+incompatible h1:eXKi9/piiC3cjJD1658mEE2o3NjkJ5vDLgYjCQu0Xlw=
 github.com/agiledragon/gomonkey v2.0.2+incompatible/go.mod h1:2NGfXu1a80LLr2cmWXGBDaHEjb1idR6+FVlX5T3D9hw=
+github.com/alicebob/miniredis/v2 v2.37.0 h1:RheObYW32G1aiJIj81XVt78ZHJpHonHLHW7OLIshq68=
+github.com/alicebob/miniredis/v2 v2.37.0/go.mod h1:TcL7YfarKPGDAthEtl5NBeHZfeUQj6OXMm/+iu5cLMM=
 github.com/alitto/pond/v2 v2.6.2 h1:Sphe40g0ILeM1pA2c2K+Th0DGU+pt0A/Kprr+WB24Pw=
 github.com/alitto/pond/v2 v2.6.2/go.mod h1:xkjYEgQ05RSpWdfSd1nM3OVv7TBhLdy7rMp3+2Nq+yE=
 github.com/andybalholm/brotli v1.2.0 h1:ukwgCxwYrmACq68yiUqwIWnGY0cTPox/M94sVwToPjQ=
@@ -372,6 +374,8 @@ github.com/wechatpay-apiv3/wechatpay-go v0.2.21 h1:uIyMpzvcaHA33W/QPtHstccw+X52H
 github.com/wechatpay-apiv3/wechatpay-go v0.2.21/go.mod h1:A254AUBVB6R+EqQFo3yTgeh7HtyqRRtN2w9hQSOrd4Q=
 github.com/xyproto/randomstring v1.0.5 h1:YtlWPoRdgMu3NZtP45drfy1GKoojuR7hmRcnhZqKjWU=
 github.com/xyproto/randomstring v1.0.5/go.mod h1:rgmS5DeNXLivK7YprL0pY+lTuhNQW3iGxZ18UQApw/E=
+github.com/yuin/gopher-lua v1.1.1 h1:kYKnWBjvbNP4XLT3+bPEwAXJx262OhaHDWDVOPjL46M=
+github.com/yuin/gopher-lua v1.1.1/go.mod h1:GBR0iDaNXjAgGg9zfCvksxSRnQx76gclCIb7kdAd1Pw=
 github.com/yusufpapurcu/wmi v1.2.4 h1:zFUKzehAFReQwLys1b/iSMl+JQGSCSjtVqQn9bBrPo0=
 github.com/yusufpapurcu/wmi v1.2.4/go.mod h1:SBZ9tNy3G9/m5Oi98Zks0QjeHVDvuK0qfxQmPyzfmi0=
 github.com/zclconf/go-cty v1.14.4 h1:uXXczd9QDGsgu0i/QFR/hzI5NYCHLf6NQw/atrbnhq8=
diff --git a/backend/internal/repository/signature_pool_cache_integration_test.go b/backend/internal/repository/signature_pool_cache_integration_test.go
new file mode 100644
index 0000000000..5e2afb179f
--- /dev/null
+++ b/backend/internal/repository/signature_pool_cache_integration_test.go
@@ -0,0 +1,205 @@
+//go:build integration
+
+package repository
+
+import (
+	"fmt"
+	"testing"
+	"time"
+
+	"github.com/Wei-Shaw/sub2api/internal/service/signature"
+	"github.com/stretchr/testify/require"
+	"github.com/stretchr/testify/suite"
+)
+
+type SignaturePoolCacheSuite struct {
+	IntegrationRedisSuite
+	pool signature.SignaturePool
+}
+
+func TestSignaturePoolCacheSuite(t *testing.T) {
+	suite.Run(t, new(SignaturePoolCacheSuite))
+}
+
+func (s *SignaturePoolCacheSuite) SetupTest() {
+	s.IntegrationRedisSuite.SetupTest()
+	s.pool = NewSignaturePoolCache(s.rdb, signature.DefaultSignatureTTL)
+}
+
+// uniqueBucket returns a test-isolated bucket to avoid cross-test pollution.
+func (s *SignaturePoolCacheSuite) uniqueBucket(suffix string) string {
+	return fmt.Sprintf("test:%s:%d", suffix, time.Now().UnixNano())
+}
+
+// --- Basic flow ---
+
+func (s *SignaturePoolCacheSuite) TestAddAndTopN_BasicFlow() {
+	bucket := s.uniqueBucket("basic")
+	now := time.Now()
+
+	s.RequireNoError(s.pool.Add(s.ctx, bucket, "sig-A", now, 10))
+	s.RequireNoError(s.pool.Add(s.ctx, bucket, "sig-B", now.Add(time.Second), 10))
+	s.RequireNoError(s.pool.Add(s.ctx, bucket, "sig-C", now.Add(2*time.Second), 10))
+
+	sigs, err := s.pool.TopN(s.ctx, bucket, 3)
+	s.RequireNoError(err)
+	// Newest first: C, B, A
+	require.Equal(s.T(), []string{"sig-C", "sig-B", "sig-A"}, sigs)
+}
+
+func (s *SignaturePoolCacheSuite) TestTopN_ReturnsFewerWhenPoolSmall() {
+	bucket := s.uniqueBucket("fewer")
+	now := time.Now()
+
+	s.RequireNoError(s.pool.Add(s.ctx, bucket, "only-one", now, 10))
+
+	sigs, err := s.pool.TopN(s.ctx, bucket, 5)
+	s.RequireNoError(err)
+	require.Equal(s.T(), []string{"only-one"}, sigs)
+}
+
+func (s *SignaturePoolCacheSuite) TestTopN_EmptyBucketReturnsNil() {
+	sigs, err := s.pool.TopN(s.ctx, s.uniqueBucket("empty"), 10)
+	s.RequireNoError(err)
+	require.Empty(s.T(), sigs)
+}
+
+// --- Capacity trimming ---
+
+func (s *SignaturePoolCacheSuite) TestAdd_TrimsToCapacity() {
+	bucket := s.uniqueBucket("cap")
+	now := time.Now()
+	cap := 3
+
+	for i := 0; i < 6; i++ {
+		sig := fmt.Sprintf("sig-%d", i)
+		s.RequireNoError(s.pool.Add(s.ctx, bucket, sig, now.Add(time.Duration(i)*time.Second), cap))
+	}
+
+	// Only the newest 3 should survive.
+	sigs, err := s.pool.TopN(s.ctx, bucket, 10)
+	s.RequireNoError(err)
+	require.Equal(s.T(), []string{"sig-5", "sig-4", "sig-3"}, sigs)
+
+	sz, err := s.pool.Size(s.ctx, bucket)
+	s.RequireNoError(err)
+	require.Equal(s.T(), int64(3), sz)
+}
+
+// --- Soft TTL lazy expiry ---
+
+func (s *SignaturePoolCacheSuite) TestAdd_EvictsExpiredEntries() {
+	bucket := s.uniqueBucket("ttl")
+	ttl := signature.DefaultSignatureTTL // 1h
+
+	// Add an entry timestamped 2 hours in the past — already expired.
+	oldTime := time.Now().Add(-2 * ttl)
+	s.RequireNoError(s.pool.Add(s.ctx, bucket, "old-sig", oldTime, 100))
+
+	// Verify it exists before a new Add triggers cleanup.
+	sz, err := s.pool.Size(s.ctx, bucket)
+	s.RequireNoError(err)
+	require.Equal(s.T(), int64(1), sz, "old entry should exist before lazy cleanup")
+
+	// Add a fresh entry — lazy cleanup should remove the expired one.
+	s.RequireNoError(s.pool.Add(s.ctx, bucket, "new-sig", time.Now(), 100))
+
+	sigs, err := s.pool.TopN(s.ctx, bucket, 10)
+	s.RequireNoError(err)
+	require.Equal(s.T(), []string{"new-sig"}, sigs, "expired entry should be evicted by lazy cleanup")
+
+	sz, err = s.pool.Size(s.ctx, bucket)
+	s.RequireNoError(err)
+	require.Equal(s.T(), int64(1), sz)
+}
+
+func (s *SignaturePoolCacheSuite) TestTopN_DoesNotFilterByTTL() {
+	// Per design: "避免没有签名可用" — expired entries survive until the next
+	// Add evicts them.
+	bucket := s.uniqueBucket("no-filter")
+	ttl := signature.DefaultSignatureTTL
+
+	oldTime := time.Now().Add(-2 * ttl)
+	s.RequireNoError(s.pool.Add(s.ctx, bucket, "stale-but-valid", oldTime, 100))
+
+	sigs, err := s.pool.TopN(s.ctx, bucket, 10)
+	s.RequireNoError(err)
+	require.Equal(s.T(), []string{"stale-but-valid"}, sigs,
+		"TopN must NOT filter by TTL — lazy expiry only happens on Add")
+}
+
+// --- De-duplication (ZADD score update) ---
+
+func (s *SignaturePoolCacheSuite) TestAdd_SameSignatureUpdatesScore() {
+	bucket := s.uniqueBucket("dedup")
+	now := time.Now()
+
+	s.RequireNoError(s.pool.Add(s.ctx, bucket, "sig-A", now, 10))
+	s.RequireNoError(s.pool.Add(s.ctx, bucket, "sig-B", now.Add(time.Second), 10))
+	// Re-add sig-A with a newer timestamp — it should move to the front.
+	s.RequireNoError(s.pool.Add(s.ctx, bucket, "sig-A", now.Add(2*time.Second), 10))
+
+	sigs, err := s.pool.TopN(s.ctx, bucket, 10)
+	s.RequireNoError(err)
+	// sig-A is now newest (score updated).
+	require.Equal(s.T(), []string{"sig-A", "sig-B"}, sigs)
+
+	sz, err := s.pool.Size(s.ctx, bucket)
+	s.RequireNoError(err)
+	require.Equal(s.T(), int64(2), sz, "duplicate should not increase pool size")
+}
+
+// --- Redis key-level TTL ---
+
+func (s *SignaturePoolCacheSuite) TestAdd_SetsKeyTTL() {
+	bucket := s.uniqueBucket("keyttl")
+	key := signaturePoolKey(bucket)
+
+	s.RequireNoError(s.pool.Add(s.ctx, bucket, "sig", time.Now(), 10))
+
+	ttl, err := s.rdb.TTL(s.ctx, key).Result()
+	s.RequireNoError(err)
+	// key TTL = softTTL * signaturePoolKeyTTLFactor = 1h * 24 = 24h.
+	// Allow a generous window for test latency.
+	s.AssertTTLWithin(ttl, 23*time.Hour, 25*time.Hour)
+}
+
+// --- Size ---
+
+func (s *SignaturePoolCacheSuite) TestSize_ReflectsCurrentEntries() {
+	bucket := s.uniqueBucket("size")
+	now := time.Now()
+
+	sz, err := s.pool.Size(s.ctx, bucket)
+	s.RequireNoError(err)
+	require.Equal(s.T(), int64(0), sz, "empty bucket")
+
+	for i := 0; i < 5; i++ {
+		s.RequireNoError(s.pool.Add(s.ctx, bucket, fmt.Sprintf("s%d", i), now.Add(time.Duration(i)*time.Second), 100))
+	}
+	sz, err = s.pool.Size(s.ctx, bucket)
+	s.RequireNoError(err)
+	require.Equal(s.T(), int64(5), sz)
+}
+
+// --- Edge cases ---
+
+func (s *SignaturePoolCacheSuite) TestAdd_EmptyBucketOrSignatureIsNoop() {
+	require.NoError(s.T(), s.pool.Add(s.ctx, "", "sig", time.Now(), 10))
+	require.NoError(s.T(), s.pool.Add(s.ctx, "b", "", time.Now(), 10))
+}
+
+func (s *SignaturePoolCacheSuite) TestTopN_EmptyBucketStringReturnsNil() {
+	sigs, err := s.pool.TopN(s.ctx, "", 10)
+	s.RequireNoError(err)
+	require.Empty(s.T(), sigs)
+}
+
+func (s *SignaturePoolCacheSuite) TestTopN_ZeroNReturnsNil() {
+	bucket := s.uniqueBucket("zeron")
+	s.RequireNoError(s.pool.Add(s.ctx, bucket, "sig", time.Now(), 10))
+
+	sigs, err := s.pool.TopN(s.ctx, bucket, 0)
+	s.RequireNoError(err)
+	require.Empty(s.T(), sigs)
+}
diff --git a/backend/internal/repository/signature_pool_cache_test.go b/backend/internal/repository/signature_pool_cache_test.go
new file mode 100644
index 0000000000..e826b625f4
--- /dev/null
+++ b/backend/internal/repository/signature_pool_cache_test.go
@@ -0,0 +1,147 @@
+//go:build unit
+
+package repository
+
+import (
+	"context"
+	"fmt"
+	"testing"
+	"time"
+
+	"github.com/Wei-Shaw/sub2api/internal/service/signature"
+	"github.com/alicebob/miniredis/v2"
+	"github.com/redis/go-redis/v9"
+	"github.com/stretchr/testify/require"
+)
+
+func setupPoolTest(t *testing.T, softTTL time.Duration) (context.Context, signature.SignaturePool) {
+	t.Helper()
+	mr := miniredis.RunT(t)
+	rdb := redis.NewClient(&redis.Options{Addr: mr.Addr()})
+	t.Cleanup(func() { _ = rdb.Close() })
+	return context.Background(), NewSignaturePoolCache(rdb, softTTL)
+}
+
+func TestSignaturePool_AddAndTopN(t *testing.T) {
+	ctx, pool := setupPoolTest(t, time.Hour)
+	now := time.Now()
+
+	require.NoError(t, pool.Add(ctx, "b", "A", now, 10))
+	require.NoError(t, pool.Add(ctx, "b", "B", now.Add(time.Second), 10))
+	require.NoError(t, pool.Add(ctx, "b", "C", now.Add(2*time.Second), 10))
+
+	sigs, err := pool.TopN(ctx, "b", 3)
+	require.NoError(t, err)
+	require.Equal(t, []string{"C", "B", "A"}, sigs)
+}
+
+func TestSignaturePool_TopN_FewerThanN(t *testing.T) {
+	ctx, pool := setupPoolTest(t, time.Hour)
+	require.NoError(t, pool.Add(ctx, "b", "only", time.Now(), 10))
+
+	sigs, err := pool.TopN(ctx, "b", 5)
+	require.NoError(t, err)
+	require.Equal(t, []string{"only"}, sigs)
+}
+
+func TestSignaturePool_TopN_EmptyBucket(t *testing.T) {
+	ctx, pool := setupPoolTest(t, time.Hour)
+	sigs, err := pool.TopN(ctx, "empty", 10)
+	require.NoError(t, err)
+	require.Empty(t, sigs)
+}
+
+func TestSignaturePool_CapacityTrim(t *testing.T) {
+	ctx, pool := setupPoolTest(t, time.Hour)
+	now := time.Now()
+
+	for i := 0; i < 6; i++ {
+		require.NoError(t, pool.Add(ctx, "b", fmt.Sprintf("s%d", i), now.Add(time.Duration(i)*time.Second), 3))
+	}
+
+	sigs, err := pool.TopN(ctx, "b", 10)
+	require.NoError(t, err)
+	require.Equal(t, []string{"s5", "s4", "s3"}, sigs)
+
+	sz, err := pool.Size(ctx, "b")
+	require.NoError(t, err)
+	require.Equal(t, int64(3), sz)
+}
+
+func TestSignaturePool_LazyExpiry(t *testing.T) {
+	ctx, pool := setupPoolTest(t, time.Hour)
+
+	oldTime := time.Now().Add(-2 * time.Hour)
+	require.NoError(t, pool.Add(ctx, "b", "old", oldTime, 100))
+
+	sz, _ := pool.Size(ctx, "b")
+	require.Equal(t, int64(1), sz, "old entry exists before cleanup")
+
+	require.NoError(t, pool.Add(ctx, "b", "new", time.Now(), 100))
+
+	sigs, err := pool.TopN(ctx, "b", 10)
+	require.NoError(t, err)
+	require.Equal(t, []string{"new"}, sigs)
+
+	sz, _ = pool.Size(ctx, "b")
+	require.Equal(t, int64(1), sz)
+}
+
+func TestSignaturePool_TopN_NoTTLFilter(t *testing.T) {
+	ctx, pool := setupPoolTest(t, time.Hour)
+
+	oldTime := time.Now().Add(-2 * time.Hour)
+	require.NoError(t, pool.Add(ctx, "b", "stale", oldTime, 100))
+
+	sigs, err := pool.TopN(ctx, "b", 10)
+	require.NoError(t, err)
+	require.Equal(t, []string{"stale"}, sigs, "TopN must not filter by TTL")
+}
+
+func TestSignaturePool_DuplicateUpdatesScore(t *testing.T) {
+	ctx, pool := setupPoolTest(t, time.Hour)
+	now := time.Now()
+
+	require.NoError(t, pool.Add(ctx, "b", "A", now, 10))
+	require.NoError(t, pool.Add(ctx, "b", "B", now.Add(time.Second), 10))
+	require.NoError(t, pool.Add(ctx, "b", "A", now.Add(2*time.Second), 10))
+
+	sigs, err := pool.TopN(ctx, "b", 10)
+	require.NoError(t, err)
+	require.Equal(t, []string{"A", "B"}, sigs)
+
+	sz, _ := pool.Size(ctx, "b")
+	require.Equal(t, int64(2), sz)
+}
+
+func TestSignaturePool_EmptyInputNoop(t *testing.T) {
+	ctx, pool := setupPoolTest(t, time.Hour)
+	require.NoError(t, pool.Add(ctx, "", "sig", time.Now(), 10))
+	require.NoError(t, pool.Add(ctx, "b", "", time.Now(), 10))
+
+	sigs, _ := pool.TopN(ctx, "", 10)
+	require.Empty(t, sigs)
+}
+
+func TestSignaturePool_ZeroN(t *testing.T) {
+	ctx, pool := setupPoolTest(t, time.Hour)
+	require.NoError(t, pool.Add(ctx, "b", "sig", time.Now(), 10))
+
+	sigs, err := pool.TopN(ctx, "b", 0)
+	require.NoError(t, err)
+	require.Empty(t, sigs)
+}
+
+func TestSignaturePool_Size(t *testing.T) {
+	ctx, pool := setupPoolTest(t, time.Hour)
+	now := time.Now()
+
+	sz, _ := pool.Size(ctx, "b")
+	require.Equal(t, int64(0), sz)
+
+	for i := 0; i < 5; i++ {
+		require.NoError(t, pool.Add(ctx, "b", fmt.Sprintf("s%d", i), now.Add(time.Duration(i)*time.Second), 100))
+	}
+	sz, _ = pool.Size(ctx, "b")
+	require.Equal(t, int64(5), sz)
+}