refactor: 消除重复的 normalizeAccountIDList，补充 PR#754 新增组件的单元测试

- 删除 account_today_stats_cache.go 中重复的 normalizeAccountIDList，统一使用 id_list_utils.go 的 normalizeInt64IDList
- 新增 snapshot_cache_test.go：覆盖 snapshotCache、buildETagFromAny、parseBoolQueryWithDefault
- 新增 id_list_utils_test.go：覆盖 normalizeInt64IDList、buildAccountTodayStatsBatchCacheKey
- 新增 ops_query_mode_test.go：覆盖 shouldFallbackOpsPreagg、cloneOpsFilterWithMode

backend/internal/handler/admin/account_handler.go

@@ -1403,7 +1403,7 @@ func (h *AccountHandler) GetBatchTodayStats(c *gin.Context) {
 		return
 	}
 
-	accountIDs := normalizeAccountIDList(req.AccountIDs)
+	accountIDs := normalizeInt64IDList(req.AccountIDs)
 	if len(accountIDs) == 0 {
 		response.Success(c, gin.H{"stats": map[string]any{}})
 		return

backend/internal/handler/admin/account_today_stats_cache.go

@@ -1,7 +1,6 @@
 package admin
 
 import (
-	"sort"
 	"strconv"
 	"strings"
 	"time"
@@ -9,26 +8,6 @@ import (
 
 var accountTodayStatsBatchCache = newSnapshotCache(30 * time.Second)
 
-func normalizeAccountIDList(accountIDs []int64) []int64 {
-	if len(accountIDs) == 0 {
-		return nil
-	}
-	seen := make(map[int64]struct{}, len(accountIDs))
-	out := make([]int64, 0, len(accountIDs))
-	for _, id := range accountIDs {
-		if id <= 0 {
-			continue
-		}
-		if _, ok := seen[id]; ok {
-			continue
-		}
-		seen[id] = struct{}{}
-		out = append(out, id)
-	}
-	sort.Slice(out, func(i, j int) bool { return out[i] < out[j] })
-	return out
-}
-
 func buildAccountTodayStatsBatchCacheKey(accountIDs []int64) string {
 	if len(accountIDs) == 0 {
 		return "accounts_today_stats_empty"

backend/internal/handler/admin/id_list_utils_test.go

@@ -0,0 +1,57 @@
+//go:build unit
+
+package admin
+
+import (
+	"testing"
+
+	"github.com/stretchr/testify/require"
+)
+
+func TestNormalizeInt64IDList(t *testing.T) {
+	tests := []struct {
+		name string
+		in   []int64
+		want []int64
+	}{
+		{"nil input", nil, nil},
+		{"empty input", []int64{}, nil},
+		{"single element", []int64{5}, []int64{5}},
+		{"already sorted unique", []int64{1, 2, 3}, []int64{1, 2, 3}},
+		{"duplicates removed", []int64{3, 1, 3, 2, 1}, []int64{1, 2, 3}},
+		{"zero filtered", []int64{0, 1, 2}, []int64{1, 2}},
+		{"negative filtered", []int64{-5, -1, 3}, []int64{3}},
+		{"all invalid", []int64{0, -1, -2}, []int64{}},
+		{"sorted output", []int64{9, 3, 7, 1}, []int64{1, 3, 7, 9}},
+	}
+
+	for _, tc := range tests {
+		t.Run(tc.name, func(t *testing.T) {
+			got := normalizeInt64IDList(tc.in)
+			if tc.want == nil {
+				require.Nil(t, got)
+			} else {
+				require.Equal(t, tc.want, got)
+			}
+		})
+	}
+}
+
+func TestBuildAccountTodayStatsBatchCacheKey(t *testing.T) {
+	tests := []struct {
+		name string
+		ids  []int64
+		want string
+	}{
+		{"empty", nil, "accounts_today_stats_empty"},
+		{"single", []int64{42}, "accounts_today_stats:42"},
+		{"multiple", []int64{1, 2, 3}, "accounts_today_stats:1,2,3"},
+	}
+
+	for _, tc := range tests {
+		t.Run(tc.name, func(t *testing.T) {
+			got := buildAccountTodayStatsBatchCacheKey(tc.ids)
+			require.Equal(t, tc.want, got)
+		})
+	}
+}

backend/internal/handler/admin/snapshot_cache_test.go

@@ -0,0 +1,128 @@
+//go:build unit
+
+package admin
+
+import (
+	"testing"
+	"time"
+
+	"github.com/stretchr/testify/require"
+)
+
+func TestSnapshotCache_SetAndGet(t *testing.T) {
+	c := newSnapshotCache(5 * time.Second)
+
+	entry := c.Set("key1", map[string]string{"hello": "world"})
+	require.NotEmpty(t, entry.ETag)
+	require.NotNil(t, entry.Payload)
+
+	got, ok := c.Get("key1")
+	require.True(t, ok)
+	require.Equal(t, entry.ETag, got.ETag)
+}
+
+func TestSnapshotCache_Expiration(t *testing.T) {
+	c := newSnapshotCache(1 * time.Millisecond)
+
+	c.Set("key1", "value")
+	time.Sleep(5 * time.Millisecond)
+
+	_, ok := c.Get("key1")
+	require.False(t, ok, "expired entry should not be returned")
+}
+
+func TestSnapshotCache_GetEmptyKey(t *testing.T) {
+	c := newSnapshotCache(5 * time.Second)
+	_, ok := c.Get("")
+	require.False(t, ok)
+}
+
+func TestSnapshotCache_GetMiss(t *testing.T) {
+	c := newSnapshotCache(5 * time.Second)
+	_, ok := c.Get("nonexistent")
+	require.False(t, ok)
+}
+
+func TestSnapshotCache_NilReceiver(t *testing.T) {
+	var c *snapshotCache
+	_, ok := c.Get("key")
+	require.False(t, ok)
+
+	entry := c.Set("key", "value")
+	require.Empty(t, entry.ETag)
+}
+
+func TestSnapshotCache_SetEmptyKey(t *testing.T) {
+	c := newSnapshotCache(5 * time.Second)
+
+	// Set with empty key should return entry but not store it
+	entry := c.Set("", "value")
+	require.NotEmpty(t, entry.ETag)
+
+	_, ok := c.Get("")
+	require.False(t, ok)
+}
+
+func TestSnapshotCache_DefaultTTL(t *testing.T) {
+	c := newSnapshotCache(0)
+	require.Equal(t, 30*time.Second, c.ttl)
+
+	c2 := newSnapshotCache(-1 * time.Second)
+	require.Equal(t, 30*time.Second, c2.ttl)
+}
+
+func TestSnapshotCache_ETagDeterministic(t *testing.T) {
+	c := newSnapshotCache(5 * time.Second)
+	payload := map[string]int{"a": 1, "b": 2}
+
+	entry1 := c.Set("k1", payload)
+	entry2 := c.Set("k2", payload)
+	require.Equal(t, entry1.ETag, entry2.ETag, "same payload should produce same ETag")
+}
+
+func TestSnapshotCache_ETagFormat(t *testing.T) {
+	c := newSnapshotCache(5 * time.Second)
+	entry := c.Set("k", "test")
+	// ETag should be quoted hex string: "abcdef..."
+	require.True(t, len(entry.ETag) > 2)
+	require.Equal(t, byte('"'), entry.ETag[0])
+	require.Equal(t, byte('"'), entry.ETag[len(entry.ETag)-1])
+}
+
+func TestBuildETagFromAny_UnmarshalablePayload(t *testing.T) {
+	// channels are not JSON-serializable
+	etag := buildETagFromAny(make(chan int))
+	require.Empty(t, etag)
+}
+
+func TestParseBoolQueryWithDefault(t *testing.T) {
+	tests := []struct {
+		name string
+		raw  string
+		def  bool
+		want bool
+	}{
+		{"empty returns default true", "", true, true},
+		{"empty returns default false", "", false, false},
+		{"1", "1", false, true},
+		{"true", "true", false, true},
+		{"TRUE", "TRUE", false, true},
+		{"yes", "yes", false, true},
+		{"on", "on", false, true},
+		{"0", "0", true, false},
+		{"false", "false", true, false},
+		{"FALSE", "FALSE", true, false},
+		{"no", "no", true, false},
+		{"off", "off", true, false},
+		{"whitespace trimmed", "  true  ", false, true},
+		{"unknown returns default true", "maybe", true, true},
+		{"unknown returns default false", "maybe", false, false},
+	}
+
+	for _, tc := range tests {
+		t.Run(tc.name, func(t *testing.T) {
+			got := parseBoolQueryWithDefault(tc.raw, tc.def)
+			require.Equal(t, tc.want, got)
+		})
+	}
+}