feat(chat): DM SSE 재연결 기반을 추가한다

app/src/test/java/kr/co/vividnext/sodalive/v2/main/chat/dm/DmChatEventClientTest.kt

@@ -66,6 +66,31 @@ class DmChatEventClientTest {
         assertEquals("안녕하세요", receivedMessage?.textMessage)
     }
 
+    @Test
+    fun `취소되지 않은 SSE stream이 EOF로 종료되면 failure callback으로 전달된다`() {
+        val failureLatch = CountDownLatch(1)
+        var failure: Throwable? = null
+        val client = clientWithResponse(
+            code = 200,
+            body = "event: connected\n\n"
+        )
+
+        client.connect(
+            token = "test-token",
+            roomId = 10L,
+            listener = object : TestListener() {
+                override fun onFailure(throwable: Throwable) {
+                    failure = throwable
+                    failureLatch.countDown()
+                }
+            }
+        )
+
+        failureLatch.await(2, TimeUnit.SECONDS)
+        assertNotNull(failure)
+        assertEquals("SSE stream closed", failure?.message)
+    }
+
     private fun clientWithResponse(
         code: Int,
         body: String