feat: 支持配置 system 消息内容格式

- 为 OpenAI 兼容模型增加字符串与文本数组两种 system content 策略

- 在 AgentScope 模型工厂统一安装兼容 formatter 并补充测试

easy-agents-agent-runtime/src/main/java/com/easyagents/agent/runtime/agentscope/AgentOpenAIChatFormatter.java

@@ -0,0 +1,31 @@
+package com.easyagents.agent.runtime.agentscope;
+
+import io.agentscope.core.formatter.openai.OpenAIChatFormatter;
+import io.agentscope.core.formatter.openai.dto.OpenAIContentPart;
+import io.agentscope.core.formatter.openai.dto.OpenAIMessage;
+import io.agentscope.core.message.Msg;
+
+import java.util.List;
+
+/**
+ * 为 OpenAI-compatible 模型补充 system content 内容块数组兼容能力。
+ */
+public final class AgentOpenAIChatFormatter extends OpenAIChatFormatter {
+
+    /**
+     * 将 AgentScope 消息转换为 OpenAI 消息，并规范 system 文本的 content 格式。
+     *
+     * @param messages AgentScope 消息
+     * @return OpenAI 请求消息
+     */
+    @Override
+    protected List<OpenAIMessage> doFormat(List<Msg> messages) {
+        List<OpenAIMessage> formattedMessages = super.doFormat(messages);
+        for (OpenAIMessage message : formattedMessages) {
+            if ("system".equals(message.getRole()) && message.getContent() instanceof String text) {
+                message.setContent(List.of(OpenAIContentPart.text(text)));
+            }
+        }
+        return formattedMessages;
+    }
+}

easy-agents-agent-runtime/src/main/java/com/easyagents/agent/runtime/agentscope/AgentScopeModelFactory.java

@@ -6,6 +6,7 @@ import com.easyagents.agent.runtime.model.AgentHttpVersionPolicy;
 import com.easyagents.agent.runtime.model.AgentModelFactory;
 import com.easyagents.agent.runtime.model.AgentModelProviderType;
 import com.easyagents.agent.runtime.model.AgentModelSpec;
+import com.easyagents.agent.runtime.model.AgentSystemContentFormat;
 import io.agentscope.core.formatter.openai.DeepSeekFormatter;
 import io.agentscope.core.formatter.openai.GLMFormatter;
 import io.agentscope.core.model.*;
@@ -153,6 +154,9 @@ public class AgentScopeModelFactory implements AgentModelFactory<Model> {
                 .stream(Boolean.TRUE.equals(options.getStream()))
                 .httpTransport(httpTransportProvider.getTransport(modelSpec.getHttpVersionPolicy(), baseUrl))
                 .generateOptions(options);
+        if (modelSpec.getSystemContentFormat() == AgentSystemContentFormat.TEXT_PARTS) {
+            builder.formatter(new AgentOpenAIChatFormatter());
+        }
         return builder.build();
     }