feat(home): AI 캐릭터 빈 스냅샷 마커를 저장한다

src/main/kotlin/kr/co/vividnext/sodalive/v2/recommendation/adapter/out/persistence/RecommendationSnapshotPersistenceAdapter.kt

@@ -18,11 +18,21 @@ class RecommendationSnapshotPersistenceAdapter(
         return repository.findLatestSnapshots(sectionType.name, offset, limit).map { it.toRecord() }
     }
 
+    override fun existsLatestSnapshot(sectionType: RecommendedSectionType): Boolean {
+        return repository.existsBySectionType(sectionType)
+    }
+
     override fun replaceSnapshots(
         sectionType: RecommendedSectionType,
         snapshotAt: LocalDateTime,
         newSnapshots: List<RecommendationSnapshotRecord>
     ) {
+        if (newSnapshots.isEmpty() && sectionType == RecommendedSectionType.AI_CHARACTER) {
+            repository.deleteBySectionType(sectionType)
+            repository.save(emptySnapshotMarker(sectionType, snapshotAt).toEntity())
+            return
+        }
+
         repository.deleteBySectionTypeAndSnapshotAt(sectionType, snapshotAt)
         repository.saveAll(newSnapshots.map { it.toEntity() })
     }
@@ -46,4 +56,21 @@ class RecommendationSnapshotPersistenceAdapter(
             randomTieBreaker = randomTieBreaker
         )
     }
+
+    private fun emptySnapshotMarker(
+        sectionType: RecommendedSectionType,
+        snapshotAt: LocalDateTime
+    ): RecommendationSnapshotRecord {
+        return RecommendationSnapshotRecord(
+            sectionType = sectionType,
+            targetId = EMPTY_SNAPSHOT_MARKER_TARGET_ID,
+            score = 0.0,
+            snapshotAt = snapshotAt,
+            randomTieBreaker = 0.0
+        )
+    }
+
+    companion object {
+        private const val EMPTY_SNAPSHOT_MARKER_TARGET_ID = 0L
+    }
 }

src/main/kotlin/kr/co/vividnext/sodalive/v2/recommendation/adapter/out/persistence/RecommendationSnapshotRepository.kt

@@ -17,6 +17,7 @@ interface RecommendationSnapshotRepository : JpaRepository<RecommendationSnapsho
                   from recommendation_snapshot latest
                   where latest.section_type = :sectionType
               )
+              and rs.target_id <> 0
             order by rs.score desc, rs.random_tie_breaker asc
             limit :limit offset :offset
         """,
@@ -29,4 +30,8 @@ interface RecommendationSnapshotRepository : JpaRepository<RecommendationSnapsho
     ): List<RecommendationSnapshot>
 
     fun deleteBySectionTypeAndSnapshotAt(sectionType: RecommendedSectionType, snapshotAt: LocalDateTime)
+
+    fun deleteBySectionType(sectionType: RecommendedSectionType)
+
+    fun existsBySectionType(sectionType: RecommendedSectionType): Boolean
 }

src/main/kotlin/kr/co/vividnext/sodalive/v2/recommendation/port/out/RecommendationSnapshotPort.kt

@@ -10,6 +10,8 @@ interface RecommendationSnapshotPort {
         limit: Int = Int.MAX_VALUE
     ): List<RecommendationSnapshotRecord>
 
+    fun existsLatestSnapshot(sectionType: RecommendedSectionType): Boolean
+
     fun replaceSnapshots(
         sectionType: RecommendedSectionType,
         snapshotAt: LocalDateTime,