src/main/kotlin/kr/co/vividnext/sodalive/admin/partner/agent/assignment/AdminAgentCreatorService.kt

@@ -1,6 +1,7 @@
 package kr.co.vividnext.sodalive.admin.partner.agent.assignment
 
 import kr.co.vividnext.sodalive.common.SodaException
+import kr.co.vividnext.sodalive.extensions.convertToUtc
 import kr.co.vividnext.sodalive.member.MemberRepository
 import kr.co.vividnext.sodalive.member.MemberRole
 import kr.co.vividnext.sodalive.partner.agent.assignment.AgentCreatorRelation
@@ -37,14 +38,15 @@ class AdminAgentCreatorService(
         }
 
         val existingRelations = relationRepository.findAllByCreatorIdOrderByAssignedAtAsc(request.creatorId)
-        if (hasAssignmentOverlap(existingRelations, request.assignedAt)) {
+        val assignedAt = request.assignedAt.convertToUtc()
+        if (hasAssignmentOverlap(existingRelations, assignedAt)) {
             throw SodaException(messageKey = "partner.agent.assignment.assignment_overlap")
         }
 
         val relation = AgentCreatorRelation()
         relation.agent = agent
         relation.creator = creator
-        relation.assignedAt = request.assignedAt
+        relation.assignedAt = assignedAt
         try {
             relationRepository.saveAndFlush(relation)
         } catch (e: DataIntegrityViolationException) {
@@ -67,11 +69,12 @@ class AdminAgentCreatorService(
 
         val assignedAt = relation.assignedAt
             ?: throw SodaException(messageKey = "partner.agent.assignment.not_found")
-        if (!request.unassignedAt.isAfter(assignedAt)) {
+        val unassignedAt = request.unassignedAt.convertToUtc()
+        if (!unassignedAt.isAfter(assignedAt)) {
             throw SodaException(messageKey = "partner.agent.assignment.invalid_unassigned_at")
         }
 
-        relation.unassignedAt = request.unassignedAt
+        relation.unassignedAt = unassignedAt
         relationRepository.save(relation)
     }
 

src/main/kotlin/kr/co/vividnext/sodalive/extensions/LocalDateTimeExtensions.kt

@@ -2,6 +2,10 @@ package kr.co.vividnext.sodalive.extensions
 
 import java.time.Duration
 import java.time.LocalDateTime
+import java.time.ZoneId
+
+private val DEFAULT_KST_ZONE_ID: ZoneId = ZoneId.of("Asia/Seoul")
+private val UTC_ZONE_ID: ZoneId = ZoneId.of("UTC")
 
 fun LocalDateTime.getTimeAgoString(): String {
     val now = LocalDateTime.now()
@@ -16,3 +20,9 @@ fun LocalDateTime.getTimeAgoString(): String {
         else -> "${duration.toDays() / 365}년전"
     }
 }
+
+fun LocalDateTime.convertToUtc(timeZone: ZoneId = DEFAULT_KST_ZONE_ID): LocalDateTime {
+    return atZone(timeZone)
+        .withZoneSameInstant(UTC_ZONE_ID)
+        .toLocalDateTime()
+}

src/test/kotlin/kr/co/vividnext/sodalive/admin/partner/agent/assignment/AdminAgentCreatorServiceTest.kt

@@ -39,6 +39,7 @@ class AdminAgentCreatorServiceTest {
     @DisplayName("관리자는 에이전트와 크리에이터를 소속으로 연결할 수 있다")
     fun shouldAssignCreatorToAgent() {
         val assignedAt = LocalDateTime.of(2026, 4, 9, 10, 0)
+        val expectedUtcAssignedAt = LocalDateTime.of(2026, 4, 9, 1, 0)
         val agent = Member(password = "password", nickname = "agent", role = MemberRole.AGENT)
         agent.id = 11L
         val creator = Member(password = "password", nickname = "creator", role = MemberRole.CREATOR)
@@ -55,7 +56,7 @@ class AdminAgentCreatorServiceTest {
         Mockito.verify(relationRepository).saveAndFlush(relationCaptor.capture())
         assertEquals(agent, relationCaptor.value.agent)
         assertEquals(creator, relationCaptor.value.creator)
-        assertEquals(assignedAt, relationCaptor.value.assignedAt)
+        assertEquals(expectedUtcAssignedAt, relationCaptor.value.assignedAt)
         assertEquals(null, relationCaptor.value.unassignedAt)
     }
 
@@ -253,6 +254,7 @@ class AdminAgentCreatorServiceTest {
     @DisplayName("종료된 이력이 있으면 이후 시각에 다시 소속 지정할 수 있다")
     fun shouldAssignCreatorWhenPreviousAssignmentAlreadyEnded() {
         val assignedAt = LocalDateTime.of(2026, 4, 9, 10, 0)
+        val previousUnassignedAt = LocalDateTime.of(2026, 4, 9, 1, 0)
         val agent = Member(password = "password", nickname = "agent", role = MemberRole.AGENT)
         agent.id = 11L
         val creator = Member(password = "password", nickname = "creator", role = MemberRole.CREATOR)
@@ -261,7 +263,7 @@ class AdminAgentCreatorServiceTest {
         existingRelation.agent = agent
         existingRelation.creator = creator
         existingRelation.assignedAt = LocalDateTime.of(2026, 4, 1, 0, 0)
-        existingRelation.unassignedAt = assignedAt
+        existingRelation.unassignedAt = previousUnassignedAt
         val request = AssignAgentCreatorRequest(agentId = 11L, creatorId = 22L, assignedAt = assignedAt)
 
         Mockito.`when`(memberRepository.findById(11L)).thenReturn(Optional.of(agent))
@@ -278,6 +280,7 @@ class AdminAgentCreatorServiceTest {
     fun shouldCloseCreatorAssignmentWindow() {
         val relation = AgentCreatorRelation()
         relation.assignedAt = LocalDateTime.of(2026, 4, 1, 0, 0)
+        val expectedUtcUnassignedAt = LocalDateTime.of(2026, 4, 9, 1, 0)
         val request = RemoveAgentCreatorRequest(
             creatorId = 22L,
             unassignedAt = LocalDateTime.of(2026, 4, 9, 10, 0)
@@ -294,10 +297,37 @@ class AdminAgentCreatorServiceTest {
 
         service.removeCreator(request)
 
-        assertEquals(request.unassignedAt, relation.unassignedAt)
+        assertEquals(expectedUtcUnassignedAt, relation.unassignedAt)
         Mockito.verify(relationRepository).save(relation)
     }
 
+    @Test
+    @DisplayName("소속 종료 시각 비교는 한국 시간 입력을 UTC로 변환한 뒤 수행한다")
+    fun shouldValidateUnassignedAtAfterConvertingKstToUtc() {
+        val relation = AgentCreatorRelation()
+        relation.assignedAt = LocalDateTime.of(2026, 4, 9, 1, 0)
+        val request = RemoveAgentCreatorRequest(
+            creatorId = 22L,
+            unassignedAt = LocalDateTime.of(2026, 4, 9, 9, 0)
+        )
+
+        Mockito.`when`(memberRepository.findByIdForUpdate(22L)).thenReturn(
+            Member(
+                password = "password",
+                nickname = "creator",
+                role = MemberRole.CREATOR
+            ).also { it.id = 22L }
+        )
+        Mockito.`when`(relationRepository.findFirstByCreatorIdAndUnassignedAtIsNull(22L)).thenReturn(relation)
+
+        val exception = assertThrows(SodaException::class.java) {
+            service.removeCreator(request)
+        }
+
+        assertEquals("partner.agent.assignment.invalid_unassigned_at", exception.messageKey)
+        Mockito.verify(relationRepository, Mockito.never()).save(Mockito.any(AgentCreatorRelation::class.java))
+    }
+
     @Test
     @DisplayName("소속 정보가 없으면 해제할 수 없다")
     fun shouldThrowWhenAssignmentDoesNotExist() {

src/test/kotlin/kr/co/vividnext/sodalive/extensions/LocalDateTimeExtensionsTest.kt

@@ -0,0 +1,37 @@
+package kr.co.vividnext.sodalive.extensions
+
+import org.junit.jupiter.api.Assertions.assertEquals
+import org.junit.jupiter.api.Assertions.fail
+import org.junit.jupiter.api.Test
+import java.time.LocalDateTime
+import java.time.ZoneId
+
+class LocalDateTimeExtensionsTest {
+    @Test
+    fun shouldConvertToUtcUsingKstByDefault() {
+        val localDateTime = LocalDateTime.of(2026, 4, 9, 10, 0)
+
+        val utcDateTime = invokeConvertToUtc(localDateTime)
+
+        assertEquals(LocalDateTime.of(2026, 4, 9, 1, 0), utcDateTime)
+    }
+
+    @Test
+    fun shouldConvertToUtcUsingProvidedTimezone() {
+        val localDateTime = LocalDateTime.of(2026, 4, 9, 10, 0)
+
+        val utcDateTime = invokeConvertToUtc(localDateTime, ZoneId.of("Asia/Bangkok"))
+
+        assertEquals(LocalDateTime.of(2026, 4, 9, 3, 0), utcDateTime)
+    }
+
+    private fun invokeConvertToUtc(localDateTime: LocalDateTime, timeZone: ZoneId = ZoneId.of("Asia/Seoul")): LocalDateTime {
+        return try {
+            val method = Class.forName("kr.co.vividnext.sodalive.extensions.LocalDateTimeExtensionsKt")
+                .getMethod("convertToUtc", LocalDateTime::class.java, ZoneId::class.java)
+            method.invoke(null, localDateTime, timeZone) as LocalDateTime
+        } catch (e: ReflectiveOperationException) {
+            fail("LocalDateTime.convertToUtc 확장함수를 찾을 수 없습니다.")
+        }
+    }
+}