feat(home): 인기 커뮤니티 fallback을 홈 조회에 연결한다

src/main/kotlin/kr/co/vividnext/sodalive/v2/recommendation/application/HomeRecommendationQueryService.kt

@@ -27,6 +27,7 @@ class HomeRecommendationQueryService(
     private val snapshotPort: RecommendationSnapshotPort,
     private val aiCharacterSnapshotFallbackService: AiCharacterSnapshotFallbackPort? = null,
     private val cheerCreatorSnapshotFallbackService: CheerCreatorSnapshotFallbackPort? = null,
+    private val popularCommunitySnapshotFallbackService: PopularCommunitySnapshotFallbackPort? = null,
     private val clock: Clock = Clock.systemUTC()
 ) {
     private val snapshotWindowPolicy = RecommendationSnapshotWindowPolicy()
@@ -129,8 +130,7 @@ class HomeRecommendationQueryService(
         memberId: Long? = null,
         includeAdultCommunities: Boolean = false
     ): List<HomePopularCommunityRecommendationRecord> {
-        val snapshots = snapshotPort.findLatestSnapshots(RecommendedSectionType.POPULAR_COMMUNITY)
+        val snapshots = findPopularCommunitySnapshotsWithFallback()
-            .take(POPULAR_COMMUNITY_CANDIDATE_LIMIT)
         val detailsById = queryPort.findPopularCommunityRecommendationDetails(
             snapshots.map { it.targetId },
             memberId,
@@ -144,6 +144,21 @@ class HomeRecommendationQueryService(
         }.take(limit)
     }
 
+    private fun findPopularCommunitySnapshotsWithFallback(): List<RecommendationSnapshotRecord> {
+        val nowUtc = LocalDateTime.now(clock)
+        val snapshotAt = snapshotWindowPolicy.previousKstDayUtcWindow(nowUtc).snapshotAt
+        val snapshots = snapshotPort.findSnapshots(
+            RecommendedSectionType.POPULAR_COMMUNITY,
+            snapshotAt,
+            limit = POPULAR_COMMUNITY_CANDIDATE_LIMIT
+        )
+        if (snapshots.isNotEmpty()) return snapshots
+        if (snapshotPort.existsSnapshot(RecommendedSectionType.POPULAR_COMMUNITY, snapshotAt)) return emptyList()
+        return popularCommunitySnapshotFallbackService
+            ?.refreshPopularCommunityIfMissing(offset = 0, limit = POPULAR_COMMUNITY_CANDIDATE_LIMIT, nowUtc = nowUtc)
+            .orEmpty()
+    }
+
     fun findGenreCreatorRecommendations(
         memberId: Long?,
         includeAdultGenres: Boolean,

src/test/kotlin/kr/co/vividnext/sodalive/v2/recommendation/application/HomeRecommendationQueryServiceTest.kt

@@ -412,9 +412,10 @@ class HomeRecommendationQueryServiceTest {
     }
 
     @Test
-    @DisplayName("인기 커뮤니티 추천은 최신 스냅샷 10개를 기준으로 크리에이터 중복을 제거하고 상세를 조립한다")
+    @DisplayName("인기 커뮤니티 추천은 대상일 스냅샷 10개를 기준으로 크리에이터 중복을 제거하고 상세를 조립한다")
-    fun shouldFindPopularCommunitiesFromLatestSnapshotsWithLimitDetailsAndCreatorUniqueness() {
+    fun shouldFindPopularCommunitiesFromTargetDaySnapshotsWithLimitDetailsAndCreatorUniqueness() {
-        val snapshotAt = LocalDateTime.of(2026, 5, 29, 23, 59, 59)
+        val service = HomeRecommendationQueryService(port, snapshotPort, clock = fixedClock())
+        val snapshotAt = LocalDateTime.of(2026, 7, 9, 14, 59, 59)
         snapshotPort.replaceSnapshots(
             RecommendedSectionType.POPULAR_COMMUNITY,
             snapshotAt,
@@ -487,7 +488,8 @@ class HomeRecommendationQueryServiceTest {
     @Test
     @DisplayName("인기 커뮤니티 추천은 상위 스냅샷 중복 제거 후 뒤 후보로 기본 10개를 채운다")
     fun shouldBackfillPopularCommunitiesAfterRemovingDuplicateCreators() {
-        val snapshotAt = LocalDateTime.of(2026, 5, 29, 23, 59, 59)
+        val service = HomeRecommendationQueryService(port, snapshotPort, clock = fixedClock())
+        val snapshotAt = LocalDateTime.of(2026, 7, 9, 14, 59, 59)
         snapshotPort.replaceSnapshots(
             RecommendedSectionType.POPULAR_COMMUNITY,
             snapshotAt,
@@ -521,6 +523,77 @@ class HomeRecommendationQueryServiceTest {
         assertEquals(communities.size, communities.map { it.creatorId }.toSet().size)
     }
 
+    @Test
+    @DisplayName("인기 커뮤니티 추천은 대상일 스냅샷이 없고 오래된 스냅샷만 있으면 fallback refresh를 호출한다")
+    fun shouldFallbackWhenOnlyStalePopularCommunitySnapshotsExist() {
+        val fallback = FakePopularCommunitySnapshotFallbackPort(
+            listOf(snapshot(RecommendedSectionType.POPULAR_COMMUNITY, 10L, 10.0, LocalDateTime.of(2026, 7, 9, 14, 59, 59)))
+        )
+        val service = HomeRecommendationQueryService(
+            port,
+            snapshotPort,
+            popularCommunitySnapshotFallbackService = fallback,
+            clock = fixedClock()
+        )
+        val staleSnapshotAt = LocalDateTime.of(2026, 7, 8, 14, 59, 59)
+        snapshotPort.replaceSnapshots(
+            RecommendedSectionType.POPULAR_COMMUNITY,
+            staleSnapshotAt,
+            listOf(snapshot(RecommendedSectionType.POPULAR_COMMUNITY, 99L, 99.0, staleSnapshotAt))
+        )
+        port.popularCommunityDetails = listOf(
+            HomePopularCommunityRecommendationRecord(
+                communityId = 10L,
+                creatorId = 110L,
+                creatorNickname = "fallback-community-creator",
+                creatorProfileImage = null,
+                imagePath = null,
+                audioPath = null,
+                content = "content",
+                price = 0,
+                createdAt = LocalDateTime.of(2026, 7, 9, 1, 0),
+                likeCount = 0L,
+                commentCount = 0L,
+                existOrdered = false,
+                isLiked = false
+            )
+        )
+
+        val communities = service.findPopularCommunityRecommendations(memberId = 105L)
+
+        assertEquals(0L, fallback.offset)
+        assertEquals(20, fallback.limit)
+        assertEquals(LocalDateTime.of(2026, 7, 9, 21, 0), fallback.nowUtc)
+        assertEquals(listOf(10L), port.popularCommunityDetailIds)
+        assertEquals(listOf(10L), communities.map { it.communityId })
+    }
+
+    @Test
+    @DisplayName("인기 커뮤니티 추천은 빈 스냅샷 refresh 완료 marker가 있으면 fallback refresh를 반복하지 않는다")
+    fun shouldNotFallbackWhenEmptyPopularCommunitySnapshotCycleExists() {
+        val fallback = FakePopularCommunitySnapshotFallbackPort(
+            listOf(snapshot(RecommendedSectionType.POPULAR_COMMUNITY, 99L, 99.0, LocalDateTime.of(2026, 7, 9, 14, 59, 59)))
+        )
+        val service = HomeRecommendationQueryService(
+            port,
+            snapshotPort,
+            popularCommunitySnapshotFallbackService = fallback,
+            clock = fixedClock()
+        )
+        snapshotPort.replaceSnapshots(
+            RecommendedSectionType.POPULAR_COMMUNITY,
+            LocalDateTime.of(2026, 7, 9, 14, 59, 59),
+            emptyList()
+        )
+
+        val communities = service.findPopularCommunityRecommendations(memberId = 105L)
+
+        assertEquals(null, fallback.offset)
+        assertEquals(null, fallback.limit)
+        assertEquals(emptyList<Long>(), port.popularCommunityDetailIds)
+        assertEquals(emptyList<HomePopularCommunityRecommendationRecord>(), communities)
+    }
+
     @Test
     @DisplayName("최신 스냅샷이 없으면 AI 캐릭터/최근 응원/인기 커뮤니티 추천은 빈 배열을 반환한다")
     fun shouldReturnEmptyListWhenLatestSnapshotsDoNotExist() {
@@ -969,7 +1042,7 @@ class HomeRecommendationQueryServiceTest {
 
         override fun findPopularCommunitySnapshots(
             windowStart: LocalDateTime,
-            snapshotAt: LocalDateTime,
+            windowEndExclusive: LocalDateTime,
             limit: Int
         ): List<RecommendationSnapshotRecord> = emptyList()
 
@@ -1071,7 +1144,9 @@ private class FakeHomeRecommendationSnapshotPort : RecommendationSnapshotPort {
     }
 
     private fun supportsEmptySnapshotMarker(sectionType: RecommendedSectionType): Boolean {
-        return sectionType == RecommendedSectionType.AI_CHARACTER || sectionType == RecommendedSectionType.CHEER_CREATOR
+        return sectionType == RecommendedSectionType.AI_CHARACTER ||
+            sectionType == RecommendedSectionType.CHEER_CREATOR ||
+            sectionType == RecommendedSectionType.POPULAR_COMMUNITY
     }
 }
 
@@ -1098,6 +1173,25 @@ private class FakeCheerCreatorSnapshotFallbackPort(
     }
 }
 
+private class FakePopularCommunitySnapshotFallbackPort(
+    private val snapshots: List<RecommendationSnapshotRecord>
+) : PopularCommunitySnapshotFallbackPort {
+    var offset: Long? = null
+    var limit: Int? = null
+    var nowUtc: LocalDateTime? = null
+
+    override fun refreshPopularCommunityIfMissing(
+        offset: Long,
+        limit: Int,
+        nowUtc: LocalDateTime
+    ): List<RecommendationSnapshotRecord> {
+        this.offset = offset
+        this.limit = limit
+        this.nowUtc = nowUtc
+        return snapshots
+    }
+}
+
 private class FakeAiCharacterSnapshotFallbackPort(
     private val snapshots: List<RecommendationSnapshotRecord>
 ) : AiCharacterSnapshotFallbackPort {