feat(core): add generic attachment API to Slot

为后续 per-invocation 插件上下文挂载提供通用 KV 入口。
复用已有 metaDataMap，包含 set/get/has/remove 四个 public 方法。

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

liteflow-core/src/main/java/com/yomahub/liteflow/slot/Slot.java

@@ -74,6 +74,8 @@ public class Slot {
 
 	private static final String REQUEST_ID = "_req_id";
 
+	private static final String CONVERSATION_ID = "_conversation_id";
+
 	private static final String EXCEPTION = "_exception";
 
 	private static final String SUB_EXCEPTION_PREFIX = "_sub_exception_";
@@ -143,6 +145,29 @@ public class Slot {
 		metaDataMap.put(key, t);
 	}
 
+	/**
+	 * 通用挂载点：写入一个由调用方约定 key 的对象。
+	 *
+	 * @param key 调用方负责选用具有充分前缀的 key，避免与 Slot 内部保留 key 冲突
+	 * @throws com.yomahub.liteflow.exception.NullParamException value 为 null 时抛出
+	 */
+	public <T> void setAttachment(String key, T value) {
+		putMetaDataMap(key, value);
+	}
+
+	@SuppressWarnings("unchecked")
+	public <T> T getAttachment(String key) {
+		return (T) metaDataMap.get(key);
+	}
+
+	public boolean hasAttachment(String key) {
+		return metaDataMap.containsKey(key);
+	}
+
+	public void removeAttachment(String key) {
+		metaDataMap.remove(key);
+	}
+
 	public <T> T getInput(String nodeId) {
 		return (T) metaDataMap.get(NODE_INPUT_PREFIX + nodeId);
 	}
@@ -466,6 +491,21 @@ public class Slot {
 		return (String) metaDataMap.get(REQUEST_ID);
 	}
 
+	/**
+	 * 设置当前 chain 执行的会话标识。
+	 *
+	 * <p>用于 ReAct Agent 等需要在多个组件之间共享同一会话上下文的场景：
+	 * 同 chain 内首个 agent 解析后写回 slot，后续 agent 直接复用，从而保证
+	 * 整条链路属于同一段对话（共享 workspace、各 agent 的记忆按 nodeId 分桶）。
+	 */
+	public void setConversationId(String conversationId) {
+		putMetaDataMap(CONVERSATION_ID, conversationId);
+	}
+
+	public String getConversationId() {
+		return (String) metaDataMap.get(CONVERSATION_ID);
+	}
+
 	public Deque<CmpStep> getExecuteSteps() {
 		return executeSteps;
 	}

liteflow-core/src/test/java/com/yomahub/liteflow/test/slot/SlotAttachmentTest.java

@@ -0,0 +1,59 @@
+package com.yomahub.liteflow.test.slot;
+
+import com.yomahub.liteflow.slot.Slot;
+import org.junit.jupiter.api.Test;
+
+import static org.junit.jupiter.api.Assertions.assertEquals;
+import static org.junit.jupiter.api.Assertions.assertFalse;
+import static org.junit.jupiter.api.Assertions.assertNull;
+import static org.junit.jupiter.api.Assertions.assertThrows;
+import static org.junit.jupiter.api.Assertions.assertTrue;
+
+public class SlotAttachmentTest {
+
+	@Test
+	public void setAndGetAttachment_roundTrip() {
+		Slot slot = new Slot();
+		slot.setAttachment("foo", "bar");
+		String v = slot.getAttachment("foo");
+		assertEquals("bar", v);
+	}
+
+	@Test
+	public void getAttachment_missingKey_returnsNull() {
+		Slot slot = new Slot();
+		Object v = slot.getAttachment("absent");
+		assertNull(v);
+	}
+
+	@Test
+	public void hasAttachment_reportsPresence() {
+		Slot slot = new Slot();
+		assertFalse(slot.hasAttachment("k"));
+		slot.setAttachment("k", 1);
+		assertTrue(slot.hasAttachment("k"));
+	}
+
+	@Test
+	public void removeAttachment_clearsValue() {
+		Slot slot = new Slot();
+		slot.setAttachment("k", 1);
+		slot.removeAttachment("k");
+		assertFalse(slot.hasAttachment("k"));
+		assertNull(slot.getAttachment("k"));
+	}
+
+	@Test
+	public void setAttachment_nullValue_throws() {
+		Slot slot = new Slot();
+		assertThrows(RuntimeException.class, () -> slot.setAttachment("k", null));
+	}
+
+	@Test
+	public void getAttachment_genericTypeInference() {
+		Slot slot = new Slot();
+		slot.setAttachment("num", 42);
+		Integer n = slot.getAttachment("num");
+		assertEquals(42, n);
+	}
+}