fix(ai-builder): Format user message to avoid markdown formatting errors (#21033)

packages/@n8n/ai-workflow-builder.ee/src/utils/stream-processor.ts

@@ -146,14 +146,37 @@ export async function* createStreamProcessor(
 	}
 }
 
+/**
+ * Remove context tags from message content that are used for AI context
+ * but shouldn't be displayed to users
+ */
+function cleanContextTags(text: string): string {
+	return text.replace(/\n*<current_workflow_json>[\s\S]*?<\/current_execution_nodes_schemas>/, '');
+}
+
 /**
  * Format a HumanMessage into the expected output format
  */
 function formatHumanMessage(msg: HumanMessage): Record<string, unknown> {
+	// Handle array content (multi-part messages with text, images, etc.)
+	if (Array.isArray(msg.content)) {
+		const textParts = msg.content.filter(
+			(c): c is { type: string; text: string } =>
+				typeof c === 'object' && c !== null && 'type' in c && c.type === 'text' && 'text' in c,
+		);
+		const text = textParts.map((part) => cleanContextTags(part.text)).join('\n');
+		return {
+			role: 'user',
+			type: 'message',
+			text,
+		};
+	}
+
+	// Handle simple string content
 	return {
 		role: 'user',
 		type: 'message',
-		text: msg.content,
+		text: cleanContextTags(msg.content),
 	};
 }
 

packages/@n8n/ai-workflow-builder.ee/src/utils/test/stream-processor.test.ts

@@ -274,6 +274,82 @@ describe('stream-processor', () => {
 			});
 		});
 
+		it('should format HumanMessage with array content (multi-part messages)', () => {
+			const messages = [
+				new HumanMessage({
+					content: [
+						{ type: 'text', text: 'Part 1' },
+						{ type: 'text', text: 'Part 2' },
+						{ type: 'image_url', image_url: 'http://example.com/image.png' },
+					],
+				}),
+			];
+
+			const result = formatMessages(messages);
+
+			expect(result).toHaveLength(1);
+			expect(result[0]).toEqual({
+				role: 'user',
+				type: 'message',
+				text: 'Part 1\nPart 2',
+			});
+		});
+
+		it('should strip context tags from HumanMessage content', () => {
+			const messageWithContext = `User question here
+<current_workflow_json>
+{"nodes": [], "connections": {}}
+</current_workflow_json>
+<current_simplified_execution_data>
+{"runData": {}}
+</current_simplified_execution_data>
+<current_execution_nodes_schemas>
+[{"nodeName": "test"}]
+</current_execution_nodes_schemas>`;
+
+			const messages = [new HumanMessage(messageWithContext)];
+
+			const result = formatMessages(messages);
+
+			expect(result).toHaveLength(1);
+			expect(result[0]).toEqual({
+				role: 'user',
+				type: 'message',
+				text: 'User question here',
+			});
+		});
+
+		it('should strip context tags from HumanMessage array content', () => {
+			const messages = [
+				new HumanMessage({
+					content: [
+						{
+							type: 'text',
+							text: `Workflow executed successfully.
+<current_workflow_json>
+{"nodes": []}
+</current_workflow_json>
+<current_simplified_execution_data>
+{"runData": {}}
+</current_simplified_execution_data>
+<current_execution_nodes_schemas>
+[{"nodeName": "Manual Trigger"}]
+</current_execution_nodes_schemas>`,
+						},
+					],
+				}),
+			];
+
+			const result = formatMessages(messages);
+
+			expect(result).toHaveLength(1);
+			expect(result[0]).toEqual({
+				role: 'user',
+				type: 'message',
+				text: 'Workflow executed successfully.',
+			});
+		});
+
 		it('should format AIMessage with text content', () => {
 			const messages = [new AIMessage('Response from AI')];