test: Retry SSE webhook setup on 404 (#28961)

Co-authored-by: Danny Martini <danny@n8n.io>
Co-authored-by: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

packages/testing/playwright/services/mcp-api-helper.ts

@@ -2,12 +2,15 @@ import type { APIResponse } from '@playwright/test';
 import * as http from 'http';
 import * as https from 'https';
 import { nanoid } from 'nanoid';
+import { setTimeout as wait } from 'node:timers/promises';
 
 import type { ApiHelpers } from './api-helper';
 import { N8N_AUTH_COOKIE } from '../config/constants';
 
 type HttpMethod = 'GET' | 'POST' | 'DELETE';
 
+class SseNotFoundError extends Error {}
+
 interface SseConnection {
 	sessionId: string;
 	postUrl: string;
@@ -176,6 +179,29 @@ export class McpApiHelper {
 	 * @returns McpSession with sessionId and postUrl for sending messages
 	 */
 	async sseSetup(
+		path: string,
+		options?: {
+			headers?: Record<string, string>;
+			maxNotFoundRetries?: number;
+			notFoundRetryDelayMs?: number;
+		},
+	): Promise<McpSession> {
+		const maxNotFoundRetries = options?.maxNotFoundRetries ?? 5;
+		const notFoundRetryDelayMs = options?.notFoundRetryDelayMs ?? 500;
+
+		for (let attempt = 0; attempt <= maxNotFoundRetries; attempt++) {
+			try {
+				return await this.attemptSseSetup(path, options);
+			} catch (error) {
+				if (!(error instanceof SseNotFoundError) || attempt === maxNotFoundRetries) throw error;
+				await wait(notFoundRetryDelayMs);
+			}
+		}
+		// unreachable: the catch above rethrows on the final attempt. Here to satisfy TS.
+		throw new Error('SSE setup: retry loop exhausted');
+	}
+
+	private async attemptSseSetup(
 		path: string,
 		options?: { headers?: Record<string, string> },
 	): Promise<McpSession> {
@@ -216,6 +242,14 @@ export class McpApiHelper {
 					headers,
 				},
 				(res) => {
+					if (res.statusCode === 404) {
+						// Drain the response so the socket is released back to the pool across retries.
+						res.resume();
+						clearTimeout(timeout);
+						reject(new SseNotFoundError(`SSE setup got 404 for ${path}`));
+						return;
+					}
+
 					let buffer = '';
 					let resolved = false;