fix(web): silence MaxListenersExceededWarning on proxied rewrites

CHANGELOG.md

@@ -7,6 +7,9 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 ## [Unreleased]
 
+### Fixed
+- Silenced a false-positive `MaxListenersExceededWarning` logged on every request proxied through an external rewrite. [#1697](https://github.com/sourcebot-dev/sourcebot/pull/1697)
+
 ## [5.1.15] - 2026-09-29
 
 ### Added

packages/web/src/instrumentation.ts

@@ -1,4 +1,5 @@
 import * as Sentry from '@sentry/nextjs';
+import type { ServerResponse } from 'node:http';
 
 export async function register() {
     if (process.env.NEXT_RUNTIME === 'nodejs') {
@@ -10,6 +11,21 @@ export async function register() {
     }
 
     if (process.env.NEXT_RUNTIME === 'nodejs') {
+        // Proxied rewrites (`/ingest/*` for PostHog, the `/monitoring` Sentry
+        // tunnel) legitimately attach 11 `close` listeners to each response: 9
+        // from Next's rewrite proxy plus 2 from Sentry. That crosses Node's
+        // default limit of 10 and logs a MaxListenersExceededWarning on every
+        // such request, even though the listeners are released with the
+        // response. The request start channel fires before Next handles the
+        // request, and scoping the raise to responses keeps the warning
+        // meaningful for every other emitter. This can be removed once Next
+        // trims its proxy listeners.
+        // @see: https://github.com/vercel/next.js/issues/97757
+        const { subscribe } = await import('node:diagnostics_channel');
+        subscribe('http.server.request.start', (message) => {
+            (message as { response?: ServerResponse }).response?.setMaxListeners(20);
+        });
+
         const { startMetricsServer } = await import('./metricsServer');
         startMetricsServer();