diff --git a/backend/db/dbsetup.py b/backend/db/dbsetup.py
index af16e2a..0007e9a 100644
--- a/backend/db/dbsetup.py
+++ b/backend/db/dbsetup.py
@@ -193,6 +193,13 @@ class DatabaseManager:
         Returns:
             sqlite3.Connection: SQLite 연결 객체
         """
+        # 연결이 닫혀있으면 재생성
+        if self.sqlite_conn is not None:
+            try:
+                self.sqlite_conn.execute("SELECT 1")
+            except Exception:
+                self.sqlite_conn = None
+
         if self.sqlite_conn is None:
             # 파일 존재 여부 확인
             is_new_db = not self.sqlite_db_path.exists()
diff --git a/backend/gui/pos_sales_gui.py b/backend/gui/pos_sales_gui.py
index 99786d5..c1f007d 100644
--- a/backend/gui/pos_sales_gui.py
+++ b/backend/gui/pos_sales_gui.py
@@ -181,8 +181,7 @@ class SalesQueryThread(QThread):
         finally:
             if mssql_conn:
                 mssql_conn.close()
-            if sqlite_conn:
-                sqlite_conn.close()
+            # sqlite_conn은 싱글톤이므로 닫지 않음 (닫으면 다른 곳에서 I/O 에러 발생)
 
 
 class QRGeneratorThread(QThread):
@@ -600,9 +599,7 @@ class UserMileageDialog(QDialog):
 
         except Exception as e:
             QMessageBox.critical(self, '오류', f'회원 정보 조회 실패:\n{str(e)}')
-        finally:
-            if conn:
-                conn.close()
+        # conn은 싱글톤이므로 닫지 않음
 
 
 class POSSalesGUI(QMainWindow):
diff --git a/backend/services/clawdbot_client.py b/backend/services/clawdbot_client.py
index 327b7a3..3031026 100644
--- a/backend/services/clawdbot_client.py
+++ b/backend/services/clawdbot_client.py
@@ -45,7 +45,7 @@ def _load_gateway_config():
 
 
 async def _ask_gateway(message, session_id='pharmacy-upsell',
-                       system_prompt=None, timeout=60):
+                       system_prompt=None, timeout=60, model=None):
     """
     Clawdbot Gateway WebSocket API 호출
 
@@ -112,7 +112,29 @@ async def _ask_gateway(message, session_id='pharmacy-upsell',
                         return None
                     break  # 연결 성공
 
-            # 4. agent 요청
+            # 4. 모델 오버라이드 (sessions.patch)
+            if model:
+                patch_id = str(uuid.uuid4())
+                patch_frame = {
+                    'type': 'req',
+                    'id': patch_id,
+                    'method': 'sessions.patch',
+                    'params': {
+                        'key': session_id,
+                        'model': model,
+                    }
+                }
+                await ws.send(json.dumps(patch_frame))
+                # patch 응답 대기
+                while True:
+                    msg = await asyncio.wait_for(ws.recv(), timeout=10)
+                    data = json.loads(msg)
+                    if data.get('id') == patch_id:
+                        if not data.get('ok'):
+                            logger.warning(f"[Clawdbot] sessions.patch 실패: {data.get('error', {}).get('message', 'unknown')}")
+                        break
+
+            # 5. agent 요청
             agent_id = str(uuid.uuid4())
             agent_params = {
                 'message': message,
@@ -174,7 +196,7 @@ async def _ask_gateway(message, session_id='pharmacy-upsell',
 
 
 def ask_clawdbot(message, session_id='pharmacy-upsell',
-                 system_prompt=None, timeout=60):
+                 system_prompt=None, timeout=60, model=None):
     """
     동기 래퍼: Flask에서 직접 호출 가능
 
@@ -183,6 +205,7 @@ def ask_clawdbot(message, session_id='pharmacy-upsell',
         session_id: 세션 ID (대화 구분용)
         system_prompt: 추가 시스템 프롬프트
         timeout: 타임아웃 (초)
+        model: 모델 오버라이드 (예: 'anthropic/claude-sonnet-4-5')
 
     Returns:
         str: AI 응답 텍스트 (실패 시 None)
@@ -190,7 +213,7 @@ def ask_clawdbot(message, session_id='pharmacy-upsell',
     try:
         loop = asyncio.new_event_loop()
         result = loop.run_until_complete(
-            _ask_gateway(message, session_id, system_prompt, timeout)
+            _ask_gateway(message, session_id, system_prompt, timeout, model=model)
         )
         loop.close()
         return result
@@ -201,6 +224,8 @@ def ask_clawdbot(message, session_id='pharmacy-upsell',
 
 # 업셀링 전용 ──────────────────────────────────────
 
+UPSELL_MODEL = 'anthropic/claude-sonnet-4-5'  # 업셀링은 Sonnet (빠르고 충분)
+
 UPSELL_SYSTEM_PROMPT = """당신은 동네 약국(청춘약국)의 친절한 약사입니다.
 고객의 구매 이력을 보고, 자연스럽고 따뜻한 톤으로 약 하나를 추천합니다.
 강압적이거나 광고 같은 느낌이 아닌, 진심으로 건강을 걱정하는 약사의 말투로 작성해주세요.
@@ -238,7 +263,8 @@ def generate_upsell(user_name, current_items, recent_products):
         prompt,
         session_id=f'upsell-{user_name}',
         system_prompt=UPSELL_SYSTEM_PROMPT,
-        timeout=30
+        timeout=30,
+        model=UPSELL_MODEL
     )
 
     if not response_text:
@@ -285,7 +311,8 @@ def generate_upsell_real(user_name, current_items, recent_products, available_pr
         prompt,
         session_id=f'upsell-real-{user_name}',
         system_prompt=UPSELL_REAL_SYSTEM_PROMPT,
-        timeout=30
+        timeout=30,
+        model=UPSELL_MODEL
     )
 
     if not response_text:
diff --git a/backend/utils/qr_token_generator.py b/backend/utils/qr_token_generator.py
index 12ee72b..8d8423b 100644
--- a/backend/utils/qr_token_generator.py
+++ b/backend/utils/qr_token_generator.py
@@ -115,8 +115,8 @@ def save_token_to_db(transaction_id, token_hash, total_amount, claimable_points,
     - token_hash가 이미 존재하면 실패 (UNIQUE 제약)
     """
     try:
-        db_manager = DatabaseManager()
-        conn = db_manager.get_sqlite_connection()
+        from db.dbsetup import db_manager as _db_manager
+        conn = _db_manager.get_sqlite_connection()
         cursor = conn.cursor()
 
         # 중복 체크 (transaction_id)