feat: 支持 Python 代码节点 main 返回输出

- 自动传入节点输入并映射 main 返回字典，兼容历史 _result

- 限制脚本输出缓冲并补充运行时与编辑器测试

- 同步 Python 帮助、占位提示和独立可执行补全片段

easyflow-modules/easyflow-module-ai/src/test/java/tech/easyflow/ai/easyagentsflow/code/PythonRuntimeEngineTest.java

@@ -31,6 +31,106 @@ public class PythonRuntimeEngineTest {
         Assert.assertEquals("dict", result.get("env_type"));
     }
 
+    @Test
+    public void testExecuteMainSuccess() {
+        Assume.assumeTrue(PythonRuntimeEngine.probe(PYTHON_COMMAND, 1500L).isAvailable());
+
+        Chain chain = createChain();
+        CodeNode node = (CodeNode) chain.getDefinition().getNodeById("code-test");
+        chain.getState().getMemory().put("ambient", "memory-value");
+        PythonRuntimeEngine engine = new PythonRuntimeEngine(
+                PYTHON_COMMAND,
+                3000L,
+                65536,
+                System.getProperty("java.io.tmpdir"));
+
+        Map<String, Object> result = engine.execute(
+                String.join("\n",
+                        "import math",
+                        "def main(inputs):",
+                        "    return {",
+                        "        'answer': inputs['input'],",
+                        "        'score': 95,",
+                        "        'sqrt': math.sqrt(16),",
+                        "        'has_ambient': 'ambient' in inputs",
+                        "    }"),
+                node,
+                chain,
+                Map.of("input", "hello"));
+
+        Assert.assertEquals("hello", result.get("answer"));
+        Assert.assertEquals(95, ((Number) result.get("score")).intValue());
+        Assert.assertEquals(4D, ((Number) result.get("sqrt")).doubleValue(), 0D);
+        Assert.assertEquals(Boolean.FALSE, result.get("has_ambient"));
+    }
+
+    @Test
+    public void testLegacyResultTakesPrecedenceOverMain() {
+        Assume.assumeTrue(PythonRuntimeEngine.probe(PYTHON_COMMAND, 1500L).isAvailable());
+
+        Chain chain = createChain();
+        CodeNode node = (CodeNode) chain.getDefinition().getNodeById("code-test");
+        PythonRuntimeEngine engine = new PythonRuntimeEngine(
+                PYTHON_COMMAND,
+                3000L,
+                65536,
+                System.getProperty("java.io.tmpdir"));
+
+        Map<String, Object> result = engine.execute(
+                String.join("\n",
+                        "_result['source'] = 'legacy'",
+                        "def main(inputs):",
+                        "    return {'source': 'main'}"),
+                node,
+                chain,
+                Map.of("input", "hello"));
+
+        Assert.assertEquals("legacy", result.get("source"));
+    }
+
+    @Test
+    public void testMainMustReturnDict() {
+        Assume.assumeTrue(PythonRuntimeEngine.probe(PYTHON_COMMAND, 1500L).isAvailable());
+
+        Chain chain = createChain();
+        CodeNode node = (CodeNode) chain.getDefinition().getNodeById("code-test");
+        PythonRuntimeEngine engine = new PythonRuntimeEngine(
+                PYTHON_COMMAND,
+                3000L,
+                65536,
+                System.getProperty("java.io.tmpdir"));
+
+        assertExecuteFail(
+                engine,
+                node,
+                chain,
+                "def main(inputs):\n    return 'invalid'",
+                "Python main 函数必须返回 dict");
+    }
+
+    @Test
+    public void testCapturedOutputIsBounded() {
+        Assume.assumeTrue(PythonRuntimeEngine.probe(PYTHON_COMMAND, 1500L).isAvailable());
+
+        Chain chain = createChain();
+        CodeNode node = (CodeNode) chain.getDefinition().getNodeById("code-test");
+        PythonRuntimeEngine engine = new PythonRuntimeEngine(
+                PYTHON_COMMAND,
+                3000L,
+                64,
+                System.getProperty("java.io.tmpdir"));
+
+        Map<String, Object> result = engine.execute(
+                String.join("\n",
+                        "import sys",
+                        "print('a' * 2048)",
+                        "_result['truncated'] = sys.stdout.truncated"),
+                node,
+                chain);
+
+        Assert.assertEquals(Boolean.TRUE, result.get("truncated"));
+    }
+
     @Test
     public void testSyntaxError() {
         Assume.assumeTrue(PythonRuntimeEngine.probe(PYTHON_COMMAND, 1500L).isAvailable());