fix(core): Fix multi-turn evals for mcp (no-changelog) (#31470)

packages/@n8n/instance-ai/evaluations/cli/build-mcp-manifest.ts

@@ -364,6 +364,26 @@ const testCaseSchema = z
 	})
 	.passthrough();
 
+function buildPromptFromConversation(
+	conversation: z.infer<typeof testCaseSchema>['conversation'],
+): string {
+	const [firstUserTurn, ...remainingUserTurns] = conversation
+		.filter((turn) => turn.role === 'user')
+		.map((turn) => turn.text.trim())
+		.filter((text) => text.length > 0);
+
+	if (!firstUserTurn) return conversation[0].text;
+	if (remainingUserTurns.length === 0) return firstUserTurn;
+
+	return [
+		firstUserTurn,
+		'Additional details from the user:',
+		...remainingUserTurns.map((turn, index) => `${String(index + 1)}. ${turn}`),
+		'',
+		"Use all details above as requirements. Configure all nodes as completely as possible and don't ask me for credentials; I'll set them up later.",
+	].join('\n\n');
+}
+
 function tailWorkflowId(text: string): string | null {
 	const matches = [...text.matchAll(/WORKFLOW_ID=([A-Za-z0-9_-]+)/g)];
 	return matches.length > 0 ? matches[matches.length - 1][1] : null;
@@ -388,7 +408,7 @@ async function buildOne(
 		? `\n\nWhen calling create_workflow_from_code, pass projectId: '${args.projectId}' so the workflow is created in that n8n project.`
 		: '';
 
-	const userMessage = `${testCase.conversation[0].text}${projectInstruction}
+	const userMessage = `${buildPromptFromConversation(testCase.conversation)}${projectInstruction}
 
 ---
 After you have created the workflow with create_workflow_from_code, print a final line of the exact form:

packages/cli/src/credentials-helper.ts

@@ -40,6 +40,7 @@ import {
 
 import { RESPONSE_ERROR_MESSAGES } from './constants';
 import { DynamicCredentialsProxy } from './credentials/dynamic-credentials-proxy';
+import { CredentialMissingIdError } from './errors/credential-missing-id.error';
 import { CredentialNotFoundError } from './errors/credential-not-found.error';
 
 import { CredentialTypes } from '@/credential-types';
@@ -291,10 +292,7 @@ export class CredentialsHelper extends ICredentialsHelper {
 		type: string,
 	): Promise<CredentialsEntity> {
 		if (!nodeCredential.id) {
-			throw new UnexpectedError('Found credential with no ID.', {
-				extra: { credentialName: nodeCredential.name },
-				tags: { credentialType: type },
-			});
+			throw new CredentialMissingIdError(nodeCredential.name, type);
 		}
 
 		let credential: CredentialsEntity;

packages/cli/src/errors/credential-missing-id.error.ts

@@ -0,0 +1,10 @@
+import { UnexpectedError } from 'n8n-workflow';
+
+export class CredentialMissingIdError extends UnexpectedError {
+	constructor(credentialName: string, credentialType: string) {
+		super('Found credential with no ID.', {
+			extra: { credentialName },
+			tags: { credentialType },
+		});
+	}
+}

packages/cli/src/modules/instance-ai/eval/__tests__/eval-mocked-credentials-helper.test.ts

@@ -11,7 +11,9 @@ import type {
 	IWorkflowExecuteAdditionalData,
 	Workflow,
 } from 'n8n-workflow';
+import { UnexpectedError } from 'n8n-workflow';
 
+import { CredentialMissingIdError } from '@/errors/credential-missing-id.error';
 import { CredentialNotFoundError } from '@/errors/credential-not-found.error';
 
 import { EvalMockedCredentialsHelper } from '../eval-mocked-credentials-helper';
@@ -88,6 +90,20 @@ describe('EvalMockedCredentialsHelper', () => {
 			expect(helper.mockedCredentials).toEqual([]);
 		});
 
+		it('rethrows generic no-id UnexpectedError errors', async () => {
+			const inner = makeInner({
+				getDecrypted: jest
+					.fn()
+					.mockRejectedValue(new UnexpectedError('Found credential with no ID.')),
+			});
+			const helper = new EvalMockedCredentialsHelper(inner);
+
+			await expect(
+				helper.getDecrypted(fakeAdditionalData, fakeNodeCreds, 'telegramApi', 'manual'),
+			).rejects.toThrow('Found credential with no ID.');
+			expect(helper.mockedCredentials).toEqual([]);
+		});
+
 		it('records "unknown" nodeName when executeData is missing', async () => {
 			const inner = makeInner({
 				getDecrypted: jest.fn().mockRejectedValue(new CredentialNotFoundError('id', 'telegramApi')),
@@ -414,8 +430,8 @@ describe('EvalMockedCredentialsHelper', () => {
 		});
 	});
 
-	describe('getDecrypted — schema synthesis when id is null', () => {
-		// `{ id: null }` short-circuits to schema synthesis without delegating to the inner helper.
+	describe('getDecrypted — schema synthesis when id is falsy', () => {
+		// Falsy credential ids short-circuit to schema synthesis without delegating to the inner helper.
 		const propsSchema = [
 			{
 				name: 'apiKey',
@@ -433,6 +449,8 @@ describe('EvalMockedCredentialsHelper', () => {
 		];
 
 		const nullNodeCreds: INodeCredentialsDetails = { id: null, name: 'openAiApi' };
+		const emptyIdNodeCreds: INodeCredentialsDetails = { id: '', name: 'openAiApi' };
+		const noIdNodeCreds = { name: 'openAiApi' } as unknown as INodeCredentialsDetails;
 
 		function makeSynthesizingInner(): ICredentialsHelper {
 			return makeInner({
@@ -442,6 +460,15 @@ describe('EvalMockedCredentialsHelper', () => {
 			});
 		}
 
+		function makeNoIdInner(): ICredentialsHelper {
+			return makeInner({
+				getCredentialsProperties: jest.fn().mockReturnValue(propsSchema),
+				getDecrypted: jest
+					.fn()
+					.mockRejectedValue(new CredentialMissingIdError('openAiApi', 'openAiApi')),
+			});
+		}
+
 		it('synthesizes a credential from the schema and applies the URL rewrite', async () => {
 			const subNodeToRoot = new Map<string, string>([['OpenAI', 'Agent']]);
 			const helper = new EvalMockedCredentialsHelper(
@@ -563,6 +590,52 @@ describe('EvalMockedCredentialsHelper', () => {
 			expect(result.url).toBe('https://api.openai.com/v1');
 			expect(helper.rewrittenCredentials).toEqual([]);
 		});
+
+		it('synthesizes a credential when the inner helper reports a missing id', async () => {
+			const helper = new EvalMockedCredentialsHelper(makeNoIdInner());
+
+			const result = await helper.getDecrypted(
+				fakeAdditionalData,
+				noIdNodeCreds,
+				'openAiApi',
+				'manual',
+				{ node: { name: 'OpenAI' } as INode } as IExecuteData,
+			);
+
+			expect(result.__evalMockedCredential).toBe(true);
+			expect(typeof result.apiKey).toBe('string');
+			expect(result.url).toBe('https://api.openai.com/v1');
+			expect(helper.mockedCredentials).toEqual([
+				{
+					nodeName: 'OpenAI',
+					credentialType: 'openAiApi',
+					credentialId: undefined,
+				},
+			]);
+		});
+
+		it('synthesizes a credential when the credential id is empty', async () => {
+			const helper = new EvalMockedCredentialsHelper(makeNoIdInner());
+
+			const result = await helper.getDecrypted(
+				fakeAdditionalData,
+				emptyIdNodeCreds,
+				'openAiApi',
+				'manual',
+				{ node: { name: 'OpenAI' } as INode } as IExecuteData,
+			);
+
+			expect(result.__evalMockedCredential).toBe(true);
+			expect(typeof result.apiKey).toBe('string');
+			expect(result.url).toBe('https://api.openai.com/v1');
+			expect(helper.mockedCredentials).toEqual([
+				{
+					nodeName: 'OpenAI',
+					credentialType: 'openAiApi',
+					credentialId: undefined,
+				},
+			]);
+		});
 	});
 
 	describe('no-id credential references — regression for "Found credential with no ID."', () => {

packages/cli/src/modules/instance-ai/eval/eval-mocked-credentials-helper.ts

@@ -31,6 +31,10 @@ export const EVAL_PROVIDER_URL_FIELD: Record<string, { field: string; pathPrefix
 	openAiApi: { field: 'url', pathPrefix: '/v1' },
 };
 
+function getCredentialId(nodeCredentials: INodeCredentialsDetails): string | undefined {
+	return nodeCredentials.id ? nodeCredentials.id : undefined;
+}
+
 /** CredentialsHelper proxy for eval: tolerates missing credentials and (optionally) rewrites vendor URLs to the wire server. */
 export class EvalMockedCredentialsHelper extends ICredentialsHelper {
 	readonly mockedCredentials: InstanceAiEvalMockedCredential[] = [];
@@ -137,7 +141,7 @@ export class EvalMockedCredentialsHelper extends ICredentialsHelper {
 			this.mockedCredentials.push({
 				nodeName: executeData?.node?.name ?? 'unknown',
 				credentialType: type,
-				credentialId: nodeCredentials.id ?? undefined,
+				credentialId: getCredentialId(nodeCredentials),
 			});
 			credentials = { [MOCK_MARKER]: true };
 		}
@@ -179,7 +183,7 @@ export class EvalMockedCredentialsHelper extends ICredentialsHelper {
 		this.rewrittenCredentials.push({
 			nodeName: subNodeName ?? 'unknown',
 			credentialType: type,
-			credentialId: nodeCredentials.id ?? undefined,
+			credentialId: getCredentialId(nodeCredentials),
 			field,
 		});