refactor: replace Trie-based digest session store with flat cache

backend/internal/service/gemini_session_integration_test.go

@@ -1,41 +1,14 @@
 package service
 
 import (
-	"context"
 	"testing"
 
 	"github.com/Wei-Shaw/sub2api/internal/pkg/antigravity"
 )
 
-// mockGeminiSessionCache 模拟 Redis 缓存
-type mockGeminiSessionCache struct {
-	sessions map[string]string // key -> value
-}
-
-func newMockGeminiSessionCache() *mockGeminiSessionCache {
-	return &mockGeminiSessionCache{sessions: make(map[string]string)}
-}
-
-func (m *mockGeminiSessionCache) Save(groupID int64, prefixHash, digestChain, uuid string, accountID int64) {
-	key := BuildGeminiSessionKey(groupID, prefixHash, digestChain)
-	value := FormatGeminiSessionValue(uuid, accountID)
-	m.sessions[key] = value
-}
-
-func (m *mockGeminiSessionCache) Find(groupID int64, prefixHash, digestChain string) (uuid string, accountID int64, found bool) {
-	prefixes := GenerateDigestChainPrefixes(digestChain)
-	for _, p := range prefixes {
-		key := BuildGeminiSessionKey(groupID, prefixHash, p)
-		if val, ok := m.sessions[key]; ok {
-			return ParseGeminiSessionValue(val)
-		}
-	}
-	return "", 0, false
-}
-
 // TestGeminiSessionContinuousConversation 测试连续会话的摘要链匹配
 func TestGeminiSessionContinuousConversation(t *testing.T) {
-	cache := newMockGeminiSessionCache()
+	store := NewDigestSessionStore()
 	groupID := int64(1)
 	prefixHash := "test_prefix_hash"
 	sessionUUID := "session-uuid-12345"
@@ -54,13 +27,13 @@ func TestGeminiSessionContinuousConversation(t *testing.T) {
 	t.Logf("Round 1 chain: %s", chain1)
 
 	// 第一轮：没有找到会话，创建新会话
-	_, _, found := cache.Find(groupID, prefixHash, chain1)
+	_, _, _, found := store.Find(groupID, prefixHash, chain1)
 	if found {
 		t.Error("Round 1: should not find existing session")
 	}
 
-	// 保存第一轮会话
-	cache.Save(groupID, prefixHash, chain1, sessionUUID, accountID)
+	// 保存第一轮会话（首轮无旧 chain）
+	store.Save(groupID, prefixHash, chain1, sessionUUID, accountID, "")
 
 	// 模拟第二轮对话（用户继续对话）
 	req2 := &antigravity.GeminiRequest{
@@ -77,7 +50,7 @@ func TestGeminiSessionContinuousConversation(t *testing.T) {
 	t.Logf("Round 2 chain: %s", chain2)
 
 	// 第二轮：应该能找到会话（通过前缀匹配）
-	foundUUID, foundAccID, found := cache.Find(groupID, prefixHash, chain2)
+	foundUUID, foundAccID, matchedChain, found := store.Find(groupID, prefixHash, chain2)
 	if !found {
 		t.Error("Round 2: should find session via prefix matching")
 	}
@@ -88,8 +61,8 @@ func TestGeminiSessionContinuousConversation(t *testing.T) {
 		t.Errorf("Round 2: expected accountID %d, got %d", accountID, foundAccID)
 	}
 
-	// 保存第二轮会话
-	cache.Save(groupID, prefixHash, chain2, sessionUUID, accountID)
+	// 保存第二轮会话，传入 Find 返回的 matchedChain 以删旧 key
+	store.Save(groupID, prefixHash, chain2, sessionUUID, accountID, matchedChain)
 
 	// 模拟第三轮对话
 	req3 := &antigravity.GeminiRequest{
@@ -108,7 +81,7 @@ func TestGeminiSessionContinuousConversation(t *testing.T) {
 	t.Logf("Round 3 chain: %s", chain3)
 
 	// 第三轮：应该能找到会话（通过第二轮的前缀匹配）
-	foundUUID, foundAccID, found = cache.Find(groupID, prefixHash, chain3)
+	foundUUID, foundAccID, _, found = store.Find(groupID, prefixHash, chain3)
 	if !found {
 		t.Error("Round 3: should find session via prefix matching")
 	}
@@ -118,13 +91,11 @@ func TestGeminiSessionContinuousConversation(t *testing.T) {
 	if foundAccID != accountID {
 		t.Errorf("Round 3: expected accountID %d, got %d", accountID, foundAccID)
 	}
-
-	t.Log("✓ Continuous conversation session matching works correctly!")
 }
 
 // TestGeminiSessionDifferentConversations 测试不同会话不会错误匹配
 func TestGeminiSessionDifferentConversations(t *testing.T) {
-	cache := newMockGeminiSessionCache()
+	store := NewDigestSessionStore()
 	groupID := int64(1)
 	prefixHash := "test_prefix_hash"
 
@@ -135,7 +106,7 @@ func TestGeminiSessionDifferentConversations(t *testing.T) {
 		},
 	}
 	chain1 := BuildGeminiDigestChain(req1)
-	cache.Save(groupID, prefixHash, chain1, "session-1", 100)
+	store.Save(groupID, prefixHash, chain1, "session-1", 100, "")
 
 	// 第二个完全不同的会话
 	req2 := &antigravity.GeminiRequest{
@@ -146,61 +117,29 @@ func TestGeminiSessionDifferentConversations(t *testing.T) {
 	chain2 := BuildGeminiDigestChain(req2)
 
 	// 不同会话不应该匹配
-	_, _, found := cache.Find(groupID, prefixHash, chain2)
+	_, _, _, found := store.Find(groupID, prefixHash, chain2)
 	if found {
 		t.Error("Different conversations should not match")
 	}
-
-	t.Log("✓ Different conversations are correctly isolated!")
 }
 
 // TestGeminiSessionPrefixMatchingOrder 测试前缀匹配的优先级（最长匹配优先）
 func TestGeminiSessionPrefixMatchingOrder(t *testing.T) {
-	cache := newMockGeminiSessionCache()
+	store := NewDigestSessionStore()
 	groupID := int64(1)
 	prefixHash := "test_prefix_hash"
 
-	// 创建一个三轮对话
-	req := &antigravity.GeminiRequest{
-		SystemInstruction: &antigravity.GeminiContent{
-			Parts: []antigravity.GeminiPart{{Text: "System prompt"}},
-		},
-		Contents: []antigravity.GeminiContent{
-			{Role: "user", Parts: []antigravity.GeminiPart{{Text: "Q1"}}},
-			{Role: "model", Parts: []antigravity.GeminiPart{{Text: "A1"}}},
-			{Role: "user", Parts: []antigravity.GeminiPart{{Text: "Q2"}}},
-		},
-	}
-	fullChain := BuildGeminiDigestChain(req)
-	prefixes := GenerateDigestChainPrefixes(fullChain)
-
-	t.Logf("Full chain: %s", fullChain)
-	t.Logf("Prefixes (longest first): %v", prefixes)
-
-	// 验证前缀生成顺序（从长到短）
-	if len(prefixes) != 4 {
-		t.Errorf("Expected 4 prefixes, got %d", len(prefixes))
-	}
-
 	// 保存不同轮次的会话到不同账号
-	// 第一轮（最短前缀）-> 账号 1
-	cache.Save(groupID, prefixHash, prefixes[3], "session-round1", 1)
-	// 第二轮 -> 账号 2
-	cache.Save(groupID, prefixHash, prefixes[2], "session-round2", 2)
-	// 第三轮（最长前缀，完整链）-> 账号 3
-	cache.Save(groupID, prefixHash, prefixes[0], "session-round3", 3)
+	store.Save(groupID, prefixHash, "s:sys-u:q1", "session-round1", 1, "")
+	store.Save(groupID, prefixHash, "s:sys-u:q1-m:a1", "session-round2", 2, "")
+	store.Save(groupID, prefixHash, "s:sys-u:q1-m:a1-u:q2", "session-round3", 3, "")
 
-	// 查找应该返回最长匹配（账号 3）
-	_, accID, found := cache.Find(groupID, prefixHash, fullChain)
+	// 查找更长的链，应该返回最长匹配（账号 3）
+	_, accID, _, found := store.Find(groupID, prefixHash, "s:sys-u:q1-m:a1-u:q2-m:a2")
 	if !found {
 		t.Error("Should find session")
 	}
 	if accID != 3 {
 		t.Errorf("Should match longest prefix (account 3), got account %d", accID)
 	}
-
-	t.Log("✓ Longest prefix matching works correctly!")
 }
-
-// 确保 context 包被使用（避免未使用的导入警告）
-var _ = context.Background