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slides/pages/agents/17.md

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+---
+layout: default
+---
+
+# Middleware: Limitar Historial (Trim)
+
+<div class="mt-4 text-xs">
+
+<v-click>
+
+```typescript
+import { RemoveMessage } from "@langchain/core/messages";
+import { createAgent, createMiddleware } from "langchain";
+import { MemorySaver, REMOVE_ALL_MESSAGES } from "@langchain/langgraph";
+
+const trimMessages = createMiddleware({
+  name: "TrimMessages",
+  beforeModel: (state) => {
+    const messages = state.messages;
+    if (messages.length <= 5) return;  // No recortar si hay pocos
+
+    // Mantener primer mensaje + últimos 4
+    const firstMsg = messages[0];
+    const recentMsgs = messages.slice(-4);
+    const newMessages = [firstMsg, ...recentMsgs];
+
+    return {
+      messages: [
+        new RemoveMessage({ id: REMOVE_ALL_MESSAGES }),
+        ...newMessages,
+      ],
+    };
+  },
+});
+
+const agent = createAgent({
+  model: "mistral:mistral-large-latest",
+  tools: [],
+  middleware: [trimMessages],
+  checkpointer: new MemorySaver(),
+});
+```
+
+</v-click>
+
+</div>