feat(content-ranking): 랭킹 공개 시각 정책을 추가한다

src/main/kotlin/kr/co/vividnext/sodalive/v2/content/ranking/domain/AudioRankingSchedulePolicy.kt

@@ -0,0 +1,25 @@
+package kr.co.vividnext.sodalive.v2.content.ranking.domain
+
+import java.time.LocalDateTime
+import java.time.LocalTime
+import java.time.ZoneId
+
+class AudioRankingSchedulePolicy {
+    fun resolveVisibleFromAt(aggregationEndAtKst: LocalDateTime): LocalDateTime {
+        return aggregationEndAtKst.toLocalDate()
+            .atTime(VISIBLE_FROM_TIME)
+            .atZone(KST_ZONE)
+            .withZoneSameInstant(UTC_ZONE)
+            .toLocalDateTime()
+    }
+
+    fun isVisible(visibleFromAtUtc: LocalDateTime, nowUtc: LocalDateTime): Boolean {
+        return !nowUtc.isBefore(visibleFromAtUtc)
+    }
+
+    companion object {
+        private val KST_ZONE: ZoneId = ZoneId.of("Asia/Seoul")
+        private val UTC_ZONE: ZoneId = ZoneId.of("UTC")
+        private val VISIBLE_FROM_TIME: LocalTime = LocalTime.of(9, 0)
+    }
+}

src/test/kotlin/kr/co/vividnext/sodalive/v2/content/ranking/domain/AudioRankingSchedulePolicyTest.kt

@@ -0,0 +1,42 @@
+package kr.co.vividnext.sodalive.v2.content.ranking.domain
+
+import org.junit.jupiter.api.Assertions.assertEquals
+import org.junit.jupiter.api.Assertions.assertFalse
+import org.junit.jupiter.api.Assertions.assertTrue
+import org.junit.jupiter.api.DisplayName
+import org.junit.jupiter.api.Test
+import java.time.LocalDateTime
+
+class AudioRankingSchedulePolicyTest {
+    private val policy = AudioRankingSchedulePolicy()
+
+    @Test
+    @DisplayName("집계 종료일과 같은 KST 날짜 09시를 UTC LocalDateTime으로 변환해 공개 시각을 산출한다")
+    fun shouldResolveVisibleFromAtAsSameKstDateNineAmConvertedToUtc() {
+        val aggregationEndAtKst = LocalDateTime.of(2026, 6, 8, 0, 0)
+
+        val visibleFromAtUtc = policy.resolveVisibleFromAt(aggregationEndAtKst)
+
+        assertEquals(LocalDateTime.of(2026, 6, 8, 0, 0), visibleFromAtUtc)
+    }
+
+    @Test
+    @DisplayName("09시 KST 이전에는 새 스냅샷을 공개하지 않는다")
+    fun shouldNotBeVisibleBeforeNineAmKst() {
+        val visibleFromAtUtc = LocalDateTime.of(2026, 6, 8, 0, 0)
+        val nowUtc = LocalDateTime.of(2026, 6, 7, 23, 59)
+
+        val visible = policy.isVisible(visibleFromAtUtc, nowUtc)
+
+        assertFalse(visible)
+    }
+
+    @Test
+    @DisplayName("09시 KST 경계와 이후에는 새 스냅샷을 공개한다")
+    fun shouldBeVisibleAtAndAfterNineAmKst() {
+        val visibleFromAtUtc = LocalDateTime.of(2026, 6, 8, 0, 0)
+
+        assertTrue(policy.isVisible(visibleFromAtUtc, LocalDateTime.of(2026, 6, 8, 0, 0)))
+        assertTrue(policy.isVisible(visibleFromAtUtc, LocalDateTime.of(2026, 6, 8, 0, 1)))
+    }
+}