fix(infra): P4-2 데몬/캐시/통계 결함 (#275+#276+#274)

#275 (데몬):
- DaemonConfigService.updateConfig: 정수 필드 가드 (비숫자/0/음수 → 400)
- DaemonScheduler: 외부 호출(scan/process) try-finally로 updateLastX 보장
  (예외 시에도 다음 cron까지 backoff)
- DaemonController.getConfig: AuthUtil.requireAdmin() 추가 (운영 설정 노출 차단)

#276 (캐시):
- CacheService 생성자: ping을 try-with-resources로 자원 누수 차단,
  ConnectionFactory null 가드
- makeKey: null/빈 parts 가드 (잘못된 키 생성 방지)

#274 (통계):
- SiteVisitStats: int → long (21억 누적 시 오버플로 방지)
- StatsMapper: getTodayVisits/getTotalVisits long 반환
- StatsService.recordVisit: 자정 경계 동시성 DataIntegrityViolationException
  1회 재시도, 2회 실패 시 1건 손실 수용 (운영 영향 미미)

후속 분리:
- #336 (#275 분산 락 + DTO + 테스트)
- #337 (#276 SCAN + 자동복구 + 메트릭)
- #338 (#274 봇/레이트리밋 + Redis INCR + 테스트)

Refs: #275 #276 #274

backend-java/src/main/java/com/tasteby/controller/DaemonController.java

@@ -19,6 +19,8 @@ public class DaemonController {
 
     @GetMapping("/config")
     public DaemonConfig getConfig() {
+        // #275 — 데몬 운영 설정은 admin 전용 (이전: 공개 노출 — 정보 누출 위험)
+        AuthUtil.requireAdmin();
         DaemonConfig config = daemonConfigService.getConfig();
         return config != null ? config : DaemonConfig.builder().build();
     }

backend-java/src/main/java/com/tasteby/domain/SiteVisitStats.java

@@ -10,6 +10,7 @@ import lombok.NoArgsConstructor;
 @NoArgsConstructor
 @AllArgsConstructor
 public class SiteVisitStats {
-    private int today;
+    // #274 — long으로 변경 (21억 이상 누적 시 int 오버플로 방지)
-    private int total;
+    private long today;
+    private long total;
 }

backend-java/src/main/java/com/tasteby/mapper/StatsMapper.java

@@ -7,7 +7,7 @@ public interface StatsMapper {
 
     void recordVisit();
 
-    int getTodayVisits();
+    long getTodayVisits();
 
-    int getTotalVisits();
+    long getTotalVisits();
 }

backend-java/src/main/java/com/tasteby/service/CacheService.java

@@ -27,8 +27,15 @@ public class CacheService {
         this.redis = redis;
         this.mapper = mapper;
         this.ttl = Duration.ofSeconds(ttlSeconds);
-        try {
+        // #276 — ping 연결 자원 누수 방지: try-with-resources
-            redis.getConnectionFactory().getConnection().ping();
+        var factory = redis.getConnectionFactory();
+        if (factory == null) {
+            log.warn("Redis ConnectionFactory is null, caching disabled");
+            disabled = true;
+            return;
+        }
+        try (var conn = factory.getConnection()) {
+            conn.ping();
             log.info("Redis connected");
         } catch (Exception e) {
             log.warn("Redis unavailable ({}), caching disabled", e.getMessage());
@@ -37,6 +44,13 @@ public class CacheService {
     }
 
     public String makeKey(String... parts) {
+        // #276 — null/빈 파트로 "tasteby::" 같은 잘못된 키 생성 방지
+        if (parts == null || parts.length == 0) {
+            throw new IllegalArgumentException("makeKey requires at least one part");
+        }
+        for (String p : parts) {
+            if (p == null) throw new IllegalArgumentException("makeKey parts must not be null");
+        }
         return PREFIX + String.join(":", parts);
     }
 

backend-java/src/main/java/com/tasteby/service/DaemonConfigService.java

@@ -2,7 +2,9 @@ package com.tasteby.service;
 
 import com.tasteby.domain.DaemonConfig;
 import com.tasteby.mapper.DaemonConfigMapper;
+import org.springframework.http.HttpStatus;
 import org.springframework.stereotype.Service;
+import org.springframework.web.server.ResponseStatusException;
 
 import java.util.Map;
 
@@ -27,20 +29,33 @@ public class DaemonConfigService {
             current.setScanEnabled(Boolean.TRUE.equals(body.get("scan_enabled")));
         }
         if (body.containsKey("scan_interval_min")) {
-            current.setScanIntervalMin(((Number) body.get("scan_interval_min")).intValue());
+            // #275 — 0/음수 입력으로 30초 사이클 폭주 방지. ClassCastException 대신 400.
+            current.setScanIntervalMin(requirePositiveInt(body.get("scan_interval_min"), "scan_interval_min"));
         }
         if (body.containsKey("process_enabled")) {
             current.setProcessEnabled(Boolean.TRUE.equals(body.get("process_enabled")));
         }
         if (body.containsKey("process_interval_min")) {
-            current.setProcessIntervalMin(((Number) body.get("process_interval_min")).intValue());
+            current.setProcessIntervalMin(requirePositiveInt(body.get("process_interval_min"), "process_interval_min"));
         }
         if (body.containsKey("process_limit")) {
-            current.setProcessLimit(((Number) body.get("process_limit")).intValue());
+            current.setProcessLimit(requirePositiveInt(body.get("process_limit"), "process_limit"));
         }
         mapper.updateConfig(current);
     }
 
+    /** #275 — 양의 정수 가드. 비숫자/0/음수는 400. */
+    private static int requirePositiveInt(Object raw, String field) {
+        if (!(raw instanceof Number n)) {
+            throw new ResponseStatusException(HttpStatus.BAD_REQUEST, field + "은(는) 정수여야 합니다");
+        }
+        int v = n.intValue();
+        if (v < 1) {
+            throw new ResponseStatusException(HttpStatus.BAD_REQUEST, field + "은(는) 1 이상이어야 합니다 (폭주 방지)");
+        }
+        return v;
+    }
+
     public void updateLastScan() {
         mapper.updateLastScan();
     }

backend-java/src/main/java/com/tasteby/service/DaemonScheduler.java

@@ -50,8 +50,13 @@ public class DaemonScheduler {
                 Instant lastScan = config.getLastScanAt() != null ? config.getLastScanAt().toInstant() : null;
                 if (lastScan == null || Instant.now().isAfter(lastScan.plus(config.getScanIntervalMin(), ChronoUnit.MINUTES))) {
                     log.info("Running scheduled channel scan...");
-                    int newVideos = youTubeService.scanAllChannels();
+                    int newVideos = 0;
-                    daemonConfigService.updateLastScan();
+                    try {
+                        newVideos = youTubeService.scanAllChannels();
+                    } finally {
+                        // #275 — 외부 호출 예외 시에도 last_scan_at을 갱신해 다음 cron까지의 backoff를 보장
+                        daemonConfigService.updateLastScan();
+                    }
                     if (newVideos > 0) {
                         cacheService.flush();
                         log.info("Scan completed: {} new videos", newVideos);
@@ -63,8 +68,12 @@ public class DaemonScheduler {
                 Instant lastProcess = config.getLastProcessAt() != null ? config.getLastProcessAt().toInstant() : null;
                 if (lastProcess == null || Instant.now().isAfter(lastProcess.plus(config.getProcessIntervalMin(), ChronoUnit.MINUTES))) {
                     log.info("Running scheduled video processing (limit={})...", config.getProcessLimit());
-                    int restaurants = pipelineService.processPending(config.getProcessLimit());
+                    int restaurants = 0;
-                    daemonConfigService.updateLastProcess();
+                    try {
+                        restaurants = pipelineService.processPending(config.getProcessLimit());
+                    } finally {
+                        daemonConfigService.updateLastProcess();
+                    }
                     if (restaurants > 0) {
                         cacheService.flush();
                         log.info("Processing completed: {} restaurants extracted", restaurants);

backend-java/src/main/java/com/tasteby/service/StatsService.java

@@ -2,11 +2,16 @@ package com.tasteby.service;
 
 import com.tasteby.domain.SiteVisitStats;
 import com.tasteby.mapper.StatsMapper;
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
+import org.springframework.dao.DataIntegrityViolationException;
 import org.springframework.stereotype.Service;
 
 @Service
 public class StatsService {
 
+    private static final Logger log = LoggerFactory.getLogger(StatsService.class);
+
     private final StatsMapper mapper;
 
     public StatsService(StatsMapper mapper) {
@@ -14,7 +19,19 @@ public class StatsService {
     }
 
     public void recordVisit() {
-        mapper.recordVisit();
+        // #274 — 자정 경계 동시성: 두 트랜잭션이 동시에 'NOT MATCHED' 판정 → 둘 다 INSERT
+        // → PK/UNIQUE 충돌 시 한 쪽 500. 1회 재시도(다음엔 MATCHED → UPDATE 분기).
+        try {
+            mapper.recordVisit();
+        } catch (DataIntegrityViolationException e) {
+            log.debug("recordVisit conflict (midnight race), retry once: {}", e.getMessage());
+            try {
+                mapper.recordVisit();
+            } catch (DataIntegrityViolationException retryFail) {
+                // 두 번째 시도도 실패: 카운트 1건 손실은 수용 (운영 영향 미미)
+                log.warn("recordVisit double-conflict, dropping one count: {}", retryFail.getMessage());
+            }
+        }
     }
 
     public SiteVisitStats getVisits() {