feat(recommend): 크리에이터 데뷔 판정 정책을 추가한다

src/main/kotlin/kr/co/vividnext/sodalive/v2/recommend/domain/CreatorDebutPolicy.kt

@@ -0,0 +1,19 @@
+package kr.co.vividnext.sodalive.v2.recommend.domain
+
+import java.time.LocalDateTime
+import java.time.temporal.ChronoUnit
+
+class CreatorDebutPolicy {
+    fun resolveDebutAt(firstContentPublishedAt: LocalDateTime?, firstLiveAt: LocalDateTime?): LocalDateTime? {
+        return listOfNotNull(firstContentPublishedAt, firstLiveAt).minOrNull()
+    }
+
+    fun isNewCreator(debutAt: LocalDateTime?, now: LocalDateTime): Boolean {
+        if (debutAt == null) {
+            return false
+        }
+
+        val days = ChronoUnit.DAYS.between(debutAt.toLocalDate(), now.toLocalDate())
+        return days in 0..30
+    }
+}

src/test/kotlin/kr/co/vividnext/sodalive/v2/recommend/domain/CreatorDebutPolicyTest.kt

@@ -0,0 +1,71 @@
+package kr.co.vividnext.sodalive.v2.recommend.domain
+
+import org.junit.jupiter.api.Assertions.assertEquals
+import org.junit.jupiter.api.Assertions.assertFalse
+import org.junit.jupiter.api.Assertions.assertNull
+import org.junit.jupiter.api.Assertions.assertTrue
+import org.junit.jupiter.api.DisplayName
+import org.junit.jupiter.api.Test
+import java.time.LocalDateTime
+
+class CreatorDebutPolicyTest {
+    private val policy = CreatorDebutPolicy()
+
+    @Test
+    @DisplayName("첫 공개 콘텐츠만 있으면 콘텐츠 공개일을 데뷔일로 선택한다")
+    fun shouldResolveDebutAtFromFirstContentOnly() {
+        val firstContentPublishedAt = LocalDateTime.of(2026, 5, 1, 10, 0)
+
+        val debutAt = policy.resolveDebutAt(firstContentPublishedAt, firstLiveAt = null)
+
+        assertEquals(firstContentPublishedAt, debutAt)
+    }
+
+    @Test
+    @DisplayName("첫 라이브만 있으면 라이브 일시를 데뷔일로 선택한다")
+    fun shouldResolveDebutAtFromFirstLiveOnly() {
+        val firstLiveAt = LocalDateTime.of(2026, 5, 2, 10, 0)
+
+        val debutAt = policy.resolveDebutAt(firstContentPublishedAt = null, firstLiveAt)
+
+        assertEquals(firstLiveAt, debutAt)
+    }
+
+    @Test
+    @DisplayName("첫 공개 콘텐츠와 첫 라이브가 모두 있으면 빠른 일시를 데뷔일로 선택한다")
+    fun shouldResolveEarliestDebutAtWhenBothExist() {
+        val firstContentPublishedAt = LocalDateTime.of(2026, 5, 3, 10, 0)
+        val firstLiveAt = LocalDateTime.of(2026, 5, 2, 10, 0)
+
+        val debutAt = policy.resolveDebutAt(firstContentPublishedAt, firstLiveAt)
+
+        assertEquals(firstLiveAt, debutAt)
+    }
+
+    @Test
+    @DisplayName("첫 공개 콘텐츠와 첫 라이브가 모두 없으면 데뷔일은 null이다")
+    fun shouldReturnNullWhenDebutSourcesDoNotExist() {
+        val debutAt = policy.resolveDebutAt(firstContentPublishedAt = null, firstLiveAt = null)
+
+        assertNull(debutAt)
+    }
+
+    @Test
+    @DisplayName("데뷔 후 30일 이내이면 신규 크리에이터로 판정한다")
+    fun shouldReturnTrueWhenCreatorIsWithinThirtyDaysFromDebut() {
+        val now = LocalDateTime.of(2026, 5, 30, 12, 0)
+
+        assertTrue(policy.isNewCreator(now.minusDays(0), now))
+        assertTrue(policy.isNewCreator(now.minusDays(30), now))
+    }
+
+    @Test
+    @DisplayName("데뷔 후 30일이 지났거나 데뷔일이 없으면 신규 크리에이터가 아니다")
+    fun shouldReturnFalseWhenCreatorIsNotWithinThirtyDaysFromDebut() {
+        val now = LocalDateTime.of(2026, 5, 30, 12, 0)
+
+        assertFalse(policy.isNewCreator(now.minusDays(31), now))
+        assertFalse(policy.isNewCreator(now.plusDays(1), now))
+        assertFalse(policy.isNewCreator(debutAt = null, now))
+    }
+}