fix: polish parameter preprocessing details

apps/api/internal/runner/param_processor_test.go

@@ -180,6 +180,44 @@ func TestParamProcessorVideoCapabilitiesNormalizeAndFilter(t *testing.T) {
 	}
 }
 
+func TestParamProcessorVideoGenerateLogsFirstFrameRemoval(t *testing.T) {
+	body := map[string]any{
+		"model":  "Seedance T2V",
+		"prompt": "animate it",
+		"content": []any{
+			map[string]any{"type": "text", "text": "animate it"},
+			map[string]any{"type": "image_url", "role": "first_frame", "image_url": "https://example.com/first.png"},
+		},
+	}
+	candidate := store.RuntimeModelCandidate{
+		ModelType: "video_generate",
+		Capabilities: map[string]any{
+			"video_generate": map[string]any{
+				"duration_range": []any{3, 12},
+			},
+		},
+	}
+
+	result := preprocessRequestWithLog("videos.generations", body, candidate)
+	for _, item := range contentItems(result.Body["content"]) {
+		if isImageContent(item) {
+			t.Fatalf("first frame image should be removed for video_generate: %+v", result.Body["content"])
+		}
+	}
+	for _, change := range result.Log.Changes {
+		if change.Path == "content[1]" {
+			if change.Reason != "模型能力未开启首帧输入，已移除 first_frame。" {
+				t.Fatalf("unexpected first frame removal reason: %+v", change)
+			}
+			if change.CapabilityPath != "capabilities.video_generate.input_first_frame" {
+				t.Fatalf("unexpected first frame capability path: %+v", change)
+			}
+			return
+		}
+	}
+	t.Fatalf("expected first frame removal log, got %+v", result.Log.Changes)
+}
+
 func TestParamProcessorImageResolutionAndOutputCount(t *testing.T) {
 	body := map[string]any{
 		"model":  "即梦V4.0",