refactor: unify server-agent to new pattern

- Change field names to snake_case (user_id, collected_info, last_recommendation, created_at, updated_at, expires_at)
- Extract system prompts to constants (SERVER_EXPERT_PROMPT, SERVER_REVIEW_PROMPT)
- Add __PASSTHROUGH__/__SESSION_END__ marker support
- Change handler signature to match other agents (db, userId, userMessage, env, options)
- Add helper functions for consistency (createServerSession, isSessionExpired, addMessageToSession, hasServerSession)
- Update saveSe rverSession signature to not need userId separately
- Rename tools constant from serverExpertTools to serverExpertTools (camelCase)
- Change AI call parameter order for consistency
- Add performance logging
- Update openai-service.ts routing to use hasServerSession
- Update server-tool.ts to use new session creation helpers
- Update message-handler.ts and api/chat.ts field references

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

src/tools/server-tool.ts

@@ -664,7 +664,7 @@ export async function executeServerAction(
   switch (action) {
     case 'start_consultation': {
       // Import session functions
-      const { saveServerSession } = await import('../agents/server-agent');
+      const { createServerSession, saveServerSession } = await import('../agents/server-agent');
 
       if (!telegramUserId) {
         return '🚫 사용자 인증이 필요합니다.';
@@ -674,16 +674,8 @@ export async function executeServerAction(
         return '🚫 세션 저장소가 설정되지 않았습니다.';
       }
 
-      const session: import('../types').ServerSession = {
-        telegramUserId,
-        status: 'gathering',
-        collectedInfo: {},
-        messages: [],
-        createdAt: Date.now(),
-        updatedAt: Date.now(),
-      };
-
-      await saveServerSession(env.DB, telegramUserId, session);
+      const session = createServerSession(telegramUserId, 'gathering');
+      await saveServerSession(env.DB, session);
 
       logger.info('상담 세션 생성', { userId: maskUserId(telegramUserId) });
 
@@ -691,7 +683,7 @@ export async function executeServerAction(
     }
 
     case 'continue_consultation': {
-      const { getServerSession, processServerConsultation } = await import('../agents/server-agent');
+      const { processServerConsultation } = await import('../agents/server-agent');
 
       if (!telegramUserId) {
         return '🚫 사용자 인증이 필요합니다.';
@@ -705,12 +697,7 @@ export async function executeServerAction(
         return '🚫 메시지가 필요합니다.';
       }
 
-      const session = await getServerSession(env.DB, telegramUserId);
-      if (!session) {
-        return '세션이 만료되었습니다. 다시 시작하려면 "서버 추천"이라고 말씀해주세요.';
-      }
-
-      const result = await processServerConsultation(args.message, session, env);
+      const result = await processServerConsultation(env.DB, telegramUserId, args.message, env);
       return result;
     }
 
@@ -771,30 +758,24 @@ export async function executeServerAction(
       // 세션에 추천 결과 저장 (선택 기능 활성화)
       if (telegramUserId && env?.DB && recommendationData.recommendations && recommendationData.recommendations.length > 0) {
         try {
-          const { getServerSession, saveServerSession } = await import('../agents/server-agent');
+          const { getServerSession, saveServerSession, createServerSession } = await import('../agents/server-agent');
 
           // 기존 세션 조회 또는 새로 생성
           let session = await getServerSession(env.DB, telegramUserId);
 
           if (!session) {
             // 세션이 없으면 새로 생성
-            session = {
-              telegramUserId,
-              status: 'selecting',
-              collectedInfo: {
-                useCase: use_case,
-                scale: expected_users <= 50 ? 'personal' : 'business',
-                expectedConcurrent: expected_users,
-              },
-              messages: [],
-              createdAt: Date.now(),
-              updatedAt: Date.now(),
+            session = createServerSession(telegramUserId, 'selecting');
+            session.collected_info = {
+              useCase: use_case,
+              scale: expected_users <= 50 ? 'personal' : 'business',
+              expectedConcurrent: expected_users,
             };
             logger.info('새 세션 생성 (추천 결과 저장용)', { userId: telegramUserId });
           }
 
-          // lastRecommendation 저장
-          session.lastRecommendation = {
+          // last_recommendation 저장
+          session.last_recommendation = {
             recommendations: recommendationData.recommendations.slice(0, 3).map(rec => ({
               pricing_id: rec.server.id,
               plan_name: rec.server.instance_name,
@@ -821,17 +802,17 @@ export async function executeServerAction(
               score: rec.score,
               max_users: rec.estimated_capacity?.max_concurrent_users || 0
             })),
-            createdAt: Date.now()
+            created_at: Date.now()
           };
 
           // status를 'selecting'으로 변경
           session.status = 'selecting';
-          session.updatedAt = Date.now();
+          session.updated_at = Date.now();
 
-          await saveServerSession(env.DB, telegramUserId, session);
+          await saveServerSession(env.DB, session);
           logger.info('추천 결과 세션 저장 완료', {
             userId: telegramUserId,
-            recommendationCount: session.lastRecommendation.recommendations.length,
+            recommendationCount: session.last_recommendation.recommendations.length,
             status: session.status
           });
         } catch (sessionError) {