refactor(receiver): 수신자 상세 애프터노트 제목의 근거 없는 nullable 을 걷는다 (closes 1177) [base: develop]

feature/afternote/data/src/test/java/com/afternote/feature/afternote/data/mapper/LeaveMessageBlockContractTest.kt

@@ -102,7 +102,7 @@ class LeaveMessageBlockContractTest {
         val detail =
             json
                 .decodeFromString<ReceivedAfternoteDetailDto>(
-                    """{"id":1,"category":"GALLERY","leaveMessage":[{"title":null,"body":"사진은 남겨줘"}]}""",
+                    """{"id":1,"category":"GALLERY","title":"사진첩","leaveMessage":[{"title":null,"body":"사진은 남겨줘"}]}""",
                 ).toDomain()
 
         assertEquals(

feature/receiver/data/src/main/kotlin/com/afternote/feature/receiver/data/dto/ReceiverAfternoteDto.kt

@@ -25,7 +25,7 @@ data class ReceivedAfternoteDto(
 data class ReceivedAfternoteDetailDto(
     @SerialName("id") val id: Long,
     @SerialName("category") val category: String? = null,
-    @SerialName("title") val title: String? = null,
+    @SerialName("title") val title: String,
     @SerialName("actions") val processingMethods: List<String> = emptyList(),
     @SerialName("leaveMessage") val leaveMessage: List<LeaveMessageBlockDto>? = null,
     @SerialName("senderName") val senderName: String? = null,

feature/receiver/data/src/test/kotlin/com/afternote/feature/receiver/data/dto/ReceivedAfternoteDetailTitleContractTest.kt

@@ -0,0 +1,64 @@
+package com.afternote.feature.receiver.data.dto
+
+import com.afternote.core.network.model.BaseResponse
+import com.afternote.core.network.model.requireData
+import com.afternote.feature.receiver.data.mapper.response.toDomain
+import kotlinx.serialization.SerializationException
+import kotlinx.serialization.json.Json
+import org.junit.Assert.assertEquals
+import org.junit.Assert.assertThrows
+import org.junit.Assert.assertTrue
+import org.junit.Test
+
+/**
+ * 수신 상세 응답의 `title` 이 **반드시 온다**는 계약 회귀 가드 (#1177).
+ *
+ * BE 는 이 값을 비워 둘 수 없다 — 생성 요청이 `@NotBlank`(`AfternoteCreateRequest`), 컬럼이
+ * `nullable = false`(`Afternote`), 수정 경로는 null 이면 기존 제목을 유지한다(`AfternoteService`).
+ * 응답 조립부 3종(social·gallery·playlist)이 그 값을 그대로 싣고, 임시저장은 수신자 조회 쿼리가
+ * `isDraft = false` 로 걸러 낸다. 그래서 제목 없는 수신 상세는 **서버에서 나올 수 없다.**
+ *
+ * 이 가드가 지키는 것은 그 계약이 깨졌을 때의 **실패 방향**이다. 예전처럼 `String? = null` 이면
+ * 키가 빠져도 파싱이 조용히 통과하고 화면이 제목 없이 열려, 서버 결함이 «제목이 비어 보이는»
+ * 정상 화면으로 위장된다. Json 설정은 `NetworkModule.provideJson` 과 동일 —
+ * `coerceInputValues` 는 **기본값이 있어야** 동작하므로 이 필드를 구해 주지 않는다.
+ */
+class ReceivedAfternoteDetailTitleContractTest {
+    private val json =
+        Json {
+            ignoreUnknownKeys = true
+            coerceInputValues = true
+        }
+
+    @Test
+    fun `제목이 있는 응답 - 디코드부터 도메인 title 까지 도달`() {
+        val payload =
+            """{"status":200,"code":200,"message":"성공","data":{"id":1,"category":"SOCIAL","title":"인스타그램","actions":["계정 삭제"],"senderName":"김철수","createdAt":"2026-08-26T14:30:00"}}"""
+
+        val detail = json.decodeFromString<BaseResponse<ReceivedAfternoteDetailDto>>(payload).requireData().toDomain()
+
+        assertEquals("인스타그램", detail.title)
+    }
+
+    @Test
+    fun `제목 키가 빠진 응답 - 빈 제목으로 성공하지 않고 어느 키인지 남기며 실패한다`() {
+        val payload =
+            """{"status":200,"code":200,"message":"성공","data":{"id":1,"category":"SOCIAL","senderName":"김철수"}}"""
+
+        assertTrue(decodeFailureMessage(payload).contains("title"))
+    }
+
+    @Test
+    fun `제목이 명시적 null 인 응답 - coerceInputValues 가 구해 주지 않는다`() {
+        val payload =
+            """{"status":200,"code":200,"message":"성공","data":{"id":1,"category":"SOCIAL","title":null}}"""
+
+        assertTrue(decodeFailureMessage(payload).contains("title"))
+    }
+
+    /** 실패 자체와 «어느 키 때문인지»를 함께 고정한다 — 진단 문구가 사라지면 서버 결함을 못 짚는다. */
+    private fun decodeFailureMessage(payload: String): String =
+        assertThrows(SerializationException::class.java) {
+            json.decodeFromString<BaseResponse<ReceivedAfternoteDetailDto>>(payload)
+        }.message.orEmpty()
+}

feature/receiver/data/src/test/kotlin/com/afternote/feature/receiver/data/mapper/response/ReceivedAfternoteDetailMapperTest.kt

@@ -36,24 +36,25 @@ class ReceivedAfternoteDetailMapperTest {
 
     @Test
     fun `toDomain - category null이면 type null`() {
-        assertNull(ReceivedAfternoteDetailDto(id = 1L, category = null).toDomain().type)
+        assertNull(ReceivedAfternoteDetailDto(id = 1L, title = "제목", category = null).toDomain().type)
     }
 
     @Test
     fun `toDomain - createdAt null이면 createdAt null`() {
-        assertNull(ReceivedAfternoteDetailDto(id = 1L, createdAt = null).toDomain().createdAt)
+        assertNull(ReceivedAfternoteDetailDto(id = 1L, title = "제목", createdAt = null).toDomain().createdAt)
     }
 
     @Test
     fun `toDomain - playlist null이면 null`() {
-        assertNull(ReceivedAfternoteDetailDto(id = 1L, playlist = null).toDomain().playlist)
+        assertNull(ReceivedAfternoteDetailDto(id = 1L, title = "제목", playlist = null).toDomain().playlist)
     }
 
     @Test
     fun `toDomain - playlist 있으면 songs·atmosphere·memorialVideo 매핑`() {
         val result =
             ReceivedAfternoteDetailDto(
                 id = 1L,
+                title = "제목",
                 playlist =
                     ReceivedPlaylistDto(
                         atmosphere = "차분",
@@ -74,6 +75,7 @@ class ReceivedAfternoteDetailMapperTest {
         val result =
             ReceivedAfternoteDetailDto(
                 id = 1L,
+                title = "제목",
                 credentials = ReceivedCredentialsDto(id = "u", password = "p"),
             ).toDomain()
 

feature/receiver/domain/src/main/java/com/afternote/feature/receiver/domain/model/ReceiverAfternoteModels.kt

@@ -20,7 +20,7 @@ data class ReceivedExportBundle(
 )
 
 data class ReceivedAfternoteDetail(
-    val title: String? = null,
+    val title: String,
     val senderName: String? = null,
     val createdAt: String? = null,
     val category: String? = null,

feature/receiver/presentation/src/main/kotlin/com/afternote/feature/receiver/presentation/detail/ReceivedAfternoteDetailSuccessMapper.kt

@@ -31,7 +31,7 @@ internal fun ReceivedAfternoteDetail.toReceivedDetailContentUiModel(): ReceivedD
 
 private fun ReceivedAfternoteDetail.toReceivedSocialNetworkDetailContent(): ReceivedSocialNetworkDetailContent =
     ReceivedSocialNetworkDetailContent(
-        serviceName = title.orEmpty(),
+        serviceName = title,
         accountId = credentials?.id.orEmpty(),
         password = credentials?.password.orEmpty(),
         processingMethods = processingMethods,
@@ -41,7 +41,7 @@ private fun ReceivedAfternoteDetail.toReceivedSocialNetworkDetailContent(): Rece
 
 private fun ReceivedAfternoteDetail.toReceivedGalleryDetailContent(): ReceivedGalleryDetailContent =
     ReceivedGalleryDetailContent(
-        serviceName = title.orEmpty(),
+        serviceName = title,
         finalWriteDate = createdAt.orEmpty(),
         processingMethods = processingMethods,
         messageBlocks = leaveMessageBlocks.toMessageBlockUiModels(),