fix(translator): add unit tests to validate output_item.done fallback logic for Gemini and Claude

internal/translator/codex/gemini/codex_gemini_response_test.go

@@ -0,0 +1,35 @@
+package gemini
+
+import (
+	"context"
+	"testing"
+
+	"github.com/tidwall/gjson"
+)
+
+func TestConvertCodexResponseToGemini_StreamEmptyOutputUsesOutputItemDoneMessageFallback(t *testing.T) {
+	ctx := context.Background()
+	originalRequest := []byte(`{"tools":[]}`)
+	var param any
+
+	chunks := [][]byte{
+		[]byte("data: {\"type\":\"response.output_item.done\",\"item\":{\"type\":\"message\",\"role\":\"assistant\",\"content\":[{\"type\":\"output_text\",\"text\":\"ok\"}]},\"output_index\":0}"),
+		[]byte("data: {\"type\":\"response.completed\",\"response\":{\"usage\":{\"input_tokens\":1,\"output_tokens\":1}}}"),
+	}
+
+	var outputs [][]byte
+	for _, chunk := range chunks {
+		outputs = append(outputs, ConvertCodexResponseToGemini(ctx, "gemini-2.5-pro", originalRequest, nil, chunk, &param)...)
+	}
+
+	found := false
+	for _, out := range outputs {
+		if gjson.GetBytes(out, "candidates.0.content.parts.0.text").String() == "ok" {
+			found = true
+			break
+		}
+	}
+	if !found {
+		t.Fatalf("expected fallback content from response.output_item.done message; outputs=%q", outputs)
+	}
+}