Fix dependency issue in history - export types for users to import so that they do not silently fail to append the message in history

Author: pietrozullo

index.ts

@@ -22,4 +22,7 @@ export { setTelemetrySource, Telemetry } from './src/telemetry/index.js'
 // Re-export StreamEvent type from LangChain for convenience
 export type { StreamEvent } from '@langchain/core/tracers/log_stream'
 
+// Re-export message classes to ensure a single constructor instance is shared by consumers
+export { BaseMessage, HumanMessage, AIMessage, SystemMessage, ToolMessage } from '@langchain/core/messages'
+
 export { BaseConnector, HttpConnector, loadConfigFile, Logger, logger, MCPAgent, MCPClient, MCPSession, StdioConnector, WebSocketConnector }

src/agents/mcp_agent.ts

@@ -14,6 +14,7 @@ import {
   AIMessage,
   HumanMessage,
   SystemMessage,
+  ToolMessage,
 } from '@langchain/core/messages'
 import { OutputParserException } from '@langchain/core/output_parsers'
 import {
@@ -690,7 +691,7 @@ export class MCPAgent {
       const historyToUse = externalHistory ?? this.conversationHistory
       const langchainHistory: BaseMessage[] = []
       for (const msg of historyToUse) {
-        if (msg instanceof HumanMessage || msg instanceof AIMessage) {
+        if (msg instanceof HumanMessage || msg instanceof AIMessage || msg instanceof ToolMessage) {
           langchainHistory.push(msg)
         }
       }