feat: 添加 Agent 步骤事件与图片附件功能

- 新增 stepStarted/stepFinished 事件类型支持
- 前端实现图片附件上传和预览功能
- 后端增强工具结果存储和事件处理
- 完善相关单元测试和集成测试

backend/tests/unit/core/agentscope/schemas/test_agui_input.py

@@ -94,3 +94,46 @@ def test_validate_run_request_messages_contract_requires_single_user_message() -
         match="RunAgentInput.messages must contain exactly one user message",
     ):
         validate_run_request_messages_contract(run_input)
+
+
+def test_validate_run_request_messages_contract_accepts_binary_url_blocks() -> None:
+    payload = _base_payload()
+    payload["messages"] = [
+        {
+            "id": "u1",
+            "role": "user",
+            "content": [
+                {"type": "text", "text": "请分析"},
+                {
+                    "type": "binary",
+                    "mimeType": "image/png",
+                    "url": "https://signed.example/a.png",
+                },
+            ],
+        }
+    ]
+    run_input = parse_run_input(payload)
+
+    validate_run_request_messages_contract(run_input)
+
+
+def test_validate_run_request_messages_contract_rejects_binary_data_block() -> None:
+    payload = _base_payload()
+    payload["messages"] = [
+        {
+            "id": "u1",
+            "role": "user",
+            "content": [
+                {"type": "text", "text": "请分析"},
+                {
+                    "type": "binary",
+                    "mimeType": "image/png",
+                    "data": "aGVsbG8=",
+                },
+            ],
+        }
+    ]
+    run_input = parse_run_input(payload)
+
+    with pytest.raises(ValueError, match="binary content requires url"):
+        validate_run_request_messages_contract(run_input)