fix(Structured Output Parser Node, Auto-fixing Output Parser Node, Tools Agent Node): Structured output improvements (#13908)

Co-authored-by: Oleg Ivaniv <me@olegivaniv.com>

packages/@n8n/nodes-langchain/utils/tests/helpers.test.ts

@@ -4,7 +4,7 @@ import { NodeOperationError } from 'n8n-workflow';
 import type { ISupplyDataFunctions, IExecuteFunctions, INode } from 'n8n-workflow';
 import { z } from 'zod';
 
-import { escapeSingleCurlyBrackets, getConnectedTools } from '../helpers';
+import { escapeSingleCurlyBrackets, getConnectedTools, unwrapNestedOutput } from '../helpers';
 import { N8nTool } from '../N8nTool';
 
 describe('escapeSingleCurlyBrackets', () => {
@@ -243,3 +243,101 @@ describe('getConnectedTools', () => {
 		expect(tools[0]).toBe(mockN8nTool);
 	});
 });
+
+describe('unwrapNestedOutput', () => {
+	it('should unwrap doubly nested output', () => {
+		const input = {
+			output: {
+				output: {
+					text: 'Hello world',
+					confidence: 0.95,
+				},
+			},
+		};
+
+		const expected = {
+			output: {
+				text: 'Hello world',
+				confidence: 0.95,
+			},
+		};
+
+		expect(unwrapNestedOutput(input)).toEqual(expected);
+	});
+
+	it('should not modify regular output object', () => {
+		const input = {
+			output: {
+				text: 'Hello world',
+				confidence: 0.95,
+			},
+		};
+
+		expect(unwrapNestedOutput(input)).toEqual(input);
+	});
+
+	it('should not modify object without output property', () => {
+		const input = {
+			result: 'success',
+			data: {
+				text: 'Hello world',
+			},
+		};
+
+		expect(unwrapNestedOutput(input)).toEqual(input);
+	});
+
+	it('should not modify when output is not an object', () => {
+		const input = {
+			output: 'Hello world',
+		};
+
+		expect(unwrapNestedOutput(input)).toEqual(input);
+	});
+
+	it('should not modify when object has multiple properties', () => {
+		const input = {
+			output: {
+				output: {
+					text: 'Hello world',
+				},
+			},
+			meta: {
+				timestamp: 123456789,
+			},
+		};
+
+		expect(unwrapNestedOutput(input)).toEqual(input);
+	});
+
+	it('should not modify when inner output has multiple properties', () => {
+		const input = {
+			output: {
+				output: {
+					text: 'Hello world',
+				},
+				meta: {
+					timestamp: 123456789,
+				},
+			},
+		};
+
+		expect(unwrapNestedOutput(input)).toEqual(input);
+	});
+
+	it('should handle null values properly', () => {
+		const input = {
+			output: null,
+		};
+
+		expect(unwrapNestedOutput(input)).toEqual(input);
+	});
+
+	it('should handle empty object values properly', () => {
+		const input = {
+			output: {},
+		};
+
+		expect(unwrapNestedOutput(input)).toEqual(input);
+	});
+});