fix(AI Agent Node): Allow removal of system message (#14407)

packages/@n8n/nodes-langchain/nodes/agents/Agent/Agent.node.ts

@@ -263,7 +263,7 @@ export class Agent implements INodeType {
 		icon: 'fa:robot',
 		iconColor: 'black',
 		group: ['transform'],
-		version: [1, 1.1, 1.2, 1.3, 1.4, 1.5, 1.6, 1.7, 1.8],
+		version: [1, 1.1, 1.2, 1.3, 1.4, 1.5, 1.6, 1.7, 1.8, 1.9],
 		description: 'Generates an action plan and executes it. Can use external tools.',
 		subtitle:
 			"={{ {	toolsAgent: 'Tools Agent', conversationalAgent: 'Conversational Agent', openAiFunctionsAgent: 'OpenAI Functions Agent', reActAgent: 'ReAct Agent', sqlAgent: 'SQL Agent', planAndExecuteAgent: 'Plan and Execute Agent' }[$parameter.agent] }}",

packages/@n8n/nodes-langchain/nodes/agents/Agent/agents/ToolsAgent/execute.ts

@@ -346,11 +346,20 @@ export async function prepareMessages(
 		outputParser?: N8nOutputParser;
 	},
 ): Promise<BaseMessagePromptTemplateLike[]> {
-	const messages: BaseMessagePromptTemplateLike[] = [
+	const useSystemMessage = options.systemMessage ?? ctx.getNode().typeVersion < 1.9;
-		['system', `{system_message}${options.outputParser ? '\n\n{formatting_instructions}' : ''}`],
+
-		['placeholder', '{chat_history}'],
+	const messages: BaseMessagePromptTemplateLike[] = [];
-		['human', '{input}'],
+
-	];
+	if (useSystemMessage) {
+		messages.push([
+			'system',
+			`{system_message}${options.outputParser ? '\n\n{formatting_instructions}' : ''}`,
+		]);
+	} else if (options.outputParser) {
+		messages.push(['system', '{formatting_instructions}']);
+	}
+
+	messages.push(['placeholder', '{chat_history}'], ['human', '{input}']);
 
 	// If there is binary data and the node option permits it, add a binary message
 	const hasBinaryData = ctx.getInputData()?.[itemIndex]?.binary !== undefined;

packages/@n8n/nodes-langchain/nodes/agents/Agent/test/ToolsAgent.test.ts

@@ -6,7 +6,7 @@ import { Buffer } from 'buffer';
 import { mock } from 'jest-mock-extended';
 import type { ToolsAgentAction } from 'langchain/dist/agents/tool_calling/output_parser';
 import type { Tool } from 'langchain/tools';
-import type { IExecuteFunctions } from 'n8n-workflow';
+import type { IExecuteFunctions, INode } from 'n8n-workflow';
 import { NodeOperationError, BINARY_ENCODING, NodeConnectionTypes } from 'n8n-workflow';
 import type { ZodType } from 'zod';
 import { z } from 'zod';
@@ -232,6 +232,75 @@ describe('prepareMessages', () => {
 		const hasHumanMessage = messages.some((m) => m instanceof HumanMessage);
 		expect(hasHumanMessage).toBe(false);
 	});
+
+	it('should not include system_message in prompt templates if not provided after version 1.9', async () => {
+		const fakeItem = { json: {} };
+		const mockNode = mock<INode>();
+		mockNode.typeVersion = 1.9;
+		mockContext.getInputData.mockReturnValue([fakeItem]);
+		mockContext.getNode.mockReturnValue(mockNode);
+		const messages = await prepareMessages(mockContext, 0, {});
+
+		expect(messages.length).toBe(3);
+		expect(messages).not.toContainEqual(['system', '{system_message}']);
+	});
+
+	it('should include system_message in prompt templates if provided after version 1.9', async () => {
+		const fakeItem = { json: {} };
+		const mockNode = mock<INode>();
+		mockNode.typeVersion = 1.9;
+		mockContext.getInputData.mockReturnValue([fakeItem]);
+		mockContext.getNode.mockReturnValue(mockNode);
+
+		const messages = await prepareMessages(mockContext, 0, { systemMessage: 'Hello' });
+
+		expect(messages.length).toBe(4);
+		expect(messages).toContainEqual(['system', '{system_message}']);
+	});
+
+	it('should include system_message in prompt templates if not provided before version 1.9', async () => {
+		const fakeItem = { json: {} };
+		const mockNode = mock<INode>();
+		mockNode.typeVersion = 1.8;
+		mockContext.getInputData.mockReturnValue([fakeItem]);
+		mockContext.getNode.mockReturnValue(mockNode);
+
+		const messages = await prepareMessages(mockContext, 0, {});
+
+		expect(messages.length).toBe(4);
+		expect(messages).toContainEqual(['system', '{system_message}']);
+	});
+
+	it('should include system_message with formatting_instructions in prompt templates if provided before version 1.9', async () => {
+		const fakeItem = { json: {} };
+		const mockNode = mock<INode>();
+		mockNode.typeVersion = 1.8;
+		mockContext.getInputData.mockReturnValue([fakeItem]);
+		mockContext.getNode.mockReturnValue(mockNode);
+
+		const messages = await prepareMessages(mockContext, 0, {
+			systemMessage: 'Hello',
+			outputParser: mock<N8nOutputParser>(),
+		});
+
+		expect(messages.length).toBe(4);
+		expect(messages).toContainEqual(['system', '{system_message}\n\n{formatting_instructions}']);
+	});
+
+	it('should add formatting instructions when omitting system message after version 1.9', async () => {
+		const fakeItem = { json: {} };
+		const mockNode = mock<INode>();
+		mockNode.typeVersion = 1.9;
+		mockContext.getInputData.mockReturnValue([fakeItem]);
+		mockContext.getNode.mockReturnValue(mockNode);
+
+		const messages = await prepareMessages(mockContext, 0, {
+			outputParser: mock<N8nOutputParser>(),
+		});
+
+		expect(messages.length).toBe(4);
+		expect(messages).toContainEqual(['system', '{formatting_instructions}']);
+	});
 });
 
 describe('preparePrompt', () => {