Split param processor and tighten Volces frame validation

apps/api/internal/clients/clients_test.go

@@ -440,6 +440,40 @@ func TestVolcesClientVideoSubmitsAndPollsTask(t *testing.T) {
 	}
 }
 
+func TestVolcesClientVideoRejectsDuplicateFirstFrameBeforeSubmit(t *testing.T) {
+	var submitted bool
+	server := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		submitted = true
+		t.Fatalf("duplicate first_frame request should not be submitted upstream")
+	}))
+	defer server.Close()
+
+	_, err := (VolcesClient{HTTPClient: server.Client()}).Run(context.Background(), Request{
+		Kind:      "videos.generations",
+		ModelType: "image_to_video",
+		Model:     "豆包Seedance",
+		Body: map[string]any{
+			"model": "豆包Seedance",
+			"content": []any{
+				map[string]any{"type": "text", "text": "animate it"},
+				map[string]any{"type": "image_url", "role": "first_frame", "image_url": map[string]any{"url": "https://example.com/first.png"}},
+				map[string]any{"type": "image_url", "role": "first_frame", "image_url": map[string]any{"url": "https://example.com/second.png"}},
+			},
+		},
+		Candidate: store.RuntimeModelCandidate{
+			BaseURL:           server.URL,
+			ProviderModelName: "doubao-seedance-1-5-pro-251215",
+			Credentials:       map[string]any{"apiKey": "volces-key"},
+		},
+	})
+	if err == nil || ErrorCode(err) != "invalid_parameter" {
+		t.Fatalf("expected local invalid_parameter error, got %v", err)
+	}
+	if submitted {
+		t.Fatal("request was submitted upstream")
+	}
+}
+
 func TestVolcesVideoBodyAllowsOnlyTaskPayloadFields(t *testing.T) {
 	body := volcesVideoBody(Request{
 		Kind:      "videos.generations",