feat(chat-room): ChatRepository 도입 및 TalkApi에 입장/메시지 조회 API 추가

- Repository 패턴 구현: 로컬 DB(Room) + 네트워크(TalkApi) 통합
- enterChatRoom, loadMoreMessages, clearAllMessagesOnLogout 제공
- TalkApi에 /enter, /messages 엔드포인트 추가
- Entity↔도메인 매퍼 추가
- Koin 모듈에 ChatRepository 바인딩

app/src/main/java/kr/co/vividnext/sodalive/chat/talk/TalkApi.kt

@@ -3,11 +3,15 @@ package kr.co.vividnext.sodalive.chat.talk
 import io.reactivex.rxjava3.core.Single
 import kr.co.vividnext.sodalive.chat.talk.room.CreateChatRoomRequest
 import kr.co.vividnext.sodalive.chat.talk.room.CreateChatRoomResponse
+import kr.co.vividnext.sodalive.chat.talk.room.ChatMessagesResponse
+import kr.co.vividnext.sodalive.chat.talk.room.ChatRoomEnterResponse
 import kr.co.vividnext.sodalive.common.ApiResponse
 import retrofit2.http.Body
 import retrofit2.http.GET
 import retrofit2.http.Header
 import retrofit2.http.POST
+import retrofit2.http.Path
+import retrofit2.http.Query
 
 interface TalkApi {
     @GET("/api/chat/room/list")
@@ -20,4 +24,20 @@ interface TalkApi {
         @Header("Authorization") authHeader: String,
         @Body request: CreateChatRoomRequest
     ): Single<ApiResponse<CreateChatRoomResponse>>
+
+    // 통합 채팅방 입장 API
+    @GET("/api/chat/rooms/{roomId}/enter")
+    fun enterChatRoom(
+        @Header("Authorization") authHeader: String,
+        @Path("roomId") roomId: Long
+    ): Single<ApiResponse<ChatRoomEnterResponse>>
+
+    // 점진적 메시지 로딩 API
+    @GET("/api/chat/rooms/{roomId}/messages")
+    fun getChatRoomMessages(
+        @Header("Authorization") authHeader: String,
+        @Path("roomId") roomId: Long,
+        @Query("cursor") cursor: Long?,
+        @Query("limit") limit: Int = 20
+    ): Single<ApiResponse<ChatMessagesResponse>>
 }

app/src/main/java/kr/co/vividnext/sodalive/chat/talk/room/ChatMessageEntityMappers.kt

@@ -0,0 +1,47 @@
+/*
+ * 보이스온 - 채팅 메시지 Entity/도메인 매퍼
+ */
+package kr.co.vividnext.sodalive.chat.talk.room
+
+import androidx.annotation.Keep
+import kr.co.vividnext.sodalive.chat.talk.room.db.ChatMessageEntity
+
+@Keep
+fun ChatMessageEntity.toDomain(): ChatMessage {
+    return ChatMessage(
+        messageId = messageId,
+        message = message,
+        profileImageUrl = profileImageUrl,
+        mine = mine,
+        createdAt = createdAt,
+        status = status,
+        localId = localId,
+        isGrouped = false
+    )
+}
+
+@Keep
+fun ChatMessage.toEntity(roomId: Long): ChatMessageEntity {
+    return ChatMessageEntity(
+        messageId = messageId,
+        roomId = roomId,
+        message = message,
+        profileImageUrl = profileImageUrl,
+        mine = mine,
+        createdAt = createdAt,
+        status = status,
+        localId = localId
+    )
+}
+
+@Keep
+fun ServerChatMessage.toEntity(roomId: Long): ChatMessageEntity {
+    return ChatMessageEntity(
+        messageId = messageId,
+        roomId = roomId,
+        message = message,
+        profileImageUrl = profileImageUrl,
+        mine = mine,
+        createdAt = createdAt
+    )
+}

app/src/main/java/kr/co/vividnext/sodalive/chat/talk/room/ChatMessagesResponse.kt

@@ -1,5 +1,5 @@
 /*
- * 보이스온 - 점진적 메시지 로딩 응답 모델
+ * 보이스온 - 점진적 메시지 로딩 응답 DTO
  */
 package kr.co.vividnext.sodalive.chat.talk.room
 

app/src/main/java/kr/co/vividnext/sodalive/chat/talk/room/ChatRepository.kt

@@ -0,0 +1,90 @@
+/*
+ * 보이스온 - 채팅방 ChatRepository (Repository 패턴)
+ * - 로컬 DB(Room) + 네트워크(TalkApi) 통합 관리
+ * - 통합 채팅방 입장 API 호출 및 로컬 동기화
+ * - 점진적 메시지 로딩
+ * - 로그아웃 시 로컬 메시지 삭제
+ */
+package kr.co.vividnext.sodalive.chat.talk.room
+
+import io.reactivex.rxjava3.core.Completable
+import io.reactivex.rxjava3.core.Single
+import io.reactivex.rxjava3.schedulers.Schedulers
+import kr.co.vividnext.sodalive.chat.talk.TalkApi
+import kr.co.vividnext.sodalive.chat.talk.room.db.ChatMessageDao
+import kr.co.vividnext.sodalive.common.ApiResponse
+import java.util.concurrent.Callable
+
+class ChatRepository(
+    private val chatDao: ChatMessageDao,
+    private val talkApi: TalkApi
+) {
+    /**
+     * 로컬에서 최근 20개 메시지 조회
+     */
+    fun getRecentMessagesFromLocal(roomId: Long): Single<List<ChatMessage>> {
+        return Single.fromCallable(Callable {
+            runCatching {
+                val entities = kotlinx.coroutines.runBlocking { chatDao.getRecentMessages(roomId) }
+                entities.map { it.toDomain() }
+            }.getOrDefault(emptyList())
+        }).subscribeOn(Schedulers.io())
+    }
+
+    /**
+     * 통합 채팅방 입장: 서버 캐릭터 정보 + 최신 메시지 수신 후 로컬 DB 업데이트
+     * - 로컬 데이터가 없더라도 서버 응답을 기준으로 동기화
+     */
+    fun enterChatRoom(token: String, roomId: Long): Single<ChatRoomEnterResponse> {
+        return talkApi.enterChatRoom(authHeader = token, roomId = roomId)
+            .subscribeOn(Schedulers.io())
+            .flatMap { response ->
+                val data = ensureSuccess(response)
+                // 로컬 DB 동기화
+                val entities = data.messages.map { it.toEntity(roomId) }
+                Single.fromCallable {
+                    kotlinx.coroutines.runBlocking { chatDao.insertMessages(entities) }
+                    data
+                }.subscribeOn(Schedulers.io())
+            }
+    }
+
+    /**
+     * 점진적 메시지 로딩: 커서 기반으로 이전 메시지를 조회
+     */
+    fun loadMoreMessages(token: String, roomId: Long, cursor: Long?): Single<ChatMessagesResponse> {
+        return talkApi.getChatRoomMessages(authHeader = token, roomId = roomId, cursor = cursor, limit = 20)
+            .subscribeOn(Schedulers.io())
+            .flatMap { response ->
+                val data = ensureMessagesSuccess(response)
+                val entities = data.messages.map { it.toEntity(roomId) }
+                Single.fromCallable {
+                    kotlinx.coroutines.runBlocking { chatDao.insertMessages(entities) }
+                    data
+                }.subscribeOn(Schedulers.io())
+            }
+    }
+
+    /**
+     * 로그아웃 시 모든 로컬 메시지 삭제
+     */
+    fun clearAllMessagesOnLogout(): Completable {
+        return Completable.fromAction {
+            kotlinx.coroutines.runBlocking { chatDao.deleteAllMessages() }
+        }.subscribeOn(Schedulers.io())
+    }
+
+    private fun <T> ensureSuccess(response: ApiResponse<T>): T {
+        if (!response.success || response.data == null) {
+            throw IllegalStateException(response.message ?: "API response error")
+        }
+        return response.data
+    }
+
+    private fun ensureMessagesSuccess(response: ApiResponse<ChatMessagesResponse>): ChatMessagesResponse {
+        if (!response.success || response.data == null) {
+            throw IllegalStateException(response.message ?: "API response error")
+        }
+        return response.data
+    }
+}

app/src/main/java/kr/co/vividnext/sodalive/chat/talk/room/ChatRoomEnterResponse.kt

@@ -1,5 +1,5 @@
 /*
- * 보이스온 - 통합 채팅방 입장 응답 모델
+ * 보이스온 - 통합 채팅방 입장 응답 DTO
  */
 package kr.co.vividnext.sodalive.chat.talk.room
 

app/src/main/java/kr/co/vividnext/sodalive/chat/talk/room/ChatTalkRoomModule.kt

@@ -1,5 +1,6 @@
 package kr.co.vividnext.sodalive.chat.talk.room
 
+import kr.co.vividnext.sodalive.chat.talk.TalkApi
 import kr.co.vividnext.sodalive.chat.talk.room.db.ChatMessageDatabase
 import org.koin.android.ext.koin.androidContext
 import org.koin.dsl.module
@@ -10,4 +11,7 @@ val chatTalkRoomModule = module {
 
     // DAO
     single { get<ChatMessageDatabase>().chatMessageDao() }
+
+    // Repository
+    single { ChatRepository(chatDao = get(), talkApi = get<TalkApi>()) }
 }