test(appserver): define turn completion status contract

Author: loong10k

src/test/java/io/github/easy4j/codex/appserver/CodexAppServerTurnTest.java

@@ -415,6 +415,30 @@ void shouldFallBackToTurnCompletedMessageWithoutItems() {
         assertEquals("fallback text", turn.future().join().getContent());
     }
 
+    @Test
+    void shouldPreserveTurnCompletionStatus() {
+        CodexAppServerTurn turn = newTurn(AppServerTurnRequest.builder().prompt("hi").build(),
+                new ThreadMappingCache(10));
+
+        handshake(turn);
+        turn.handleFrame("{\"jsonrpc\":\"2.0\",\"id\":2,\"result\":{\"thread\":{\"id\":\"th_1\"}}}");
+        turn.handleFrame("{\"method\":\"turn/completed\",\"params\":{\"turn\":{\"status\":\"completed\"}}}");
+
+        assertEquals("completed", turn.future().join().getFinishReason());
+    }
+
+    @Test
+    void shouldUseCompletedFinishReasonWhenServerOmitsStatus() {
+        CodexAppServerTurn turn = newTurn(AppServerTurnRequest.builder().prompt("hi").build(),
+                new ThreadMappingCache(10));
+
+        handshake(turn);
+        turn.handleFrame("{\"jsonrpc\":\"2.0\",\"id\":2,\"result\":{\"thread\":{\"id\":\"th_1\"}}}");
+        turn.handleFrame("{\"method\":\"turn/completed\",\"params\":{}}");
+
+        assertEquals("completed", turn.future().join().getFinishReason());
+    }
+
     @Test
     void shouldRememberThreadMappingOnTurnCompleted() {
         ThreadMappingCache cache = new ThreadMappingCache(10);