Use startsWith() for perf test URL check to prevent false positives

[Copilot]

The special response URL check /test/perf-test-mock could match legitimate Slack URLs containing this substring anywhere in the path, causing incorrect mock behavior.

Change:

// Before: substring match anywhere in URL
if (responseUrl.includes('/test/perf-test-mock')) {

// After: exact prefix match
if (responseUrl.startsWith('https://hooks.slack.com/test/perf-test-mock')) {

This prevents false positives on URLs like https://hooks.slack.com/services/T123/B456/xyz/test/perf-test-mock/abc while correctly matching the exact mock URL generated by performance tests.

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[Copilot]

Just as a heads up, I was blocked by some firewall rules while working on your feedback. Expand below for details.

Warning

Firewall rules blocked me from connecting to one or more addresses (expand for details)

I tried to connect to the following addresses, but was blocked by firewall rules:

• googlechromelabs.github.io
  • Triggering command: /usr/local/bin/node node install.mjs (dns block)
• https://storage.googleapis.com/chrome-for-testing-public/143.0.7499.169/linux64/chrome-linux64.zip
  • Triggering command: /usr/local/bin/node node install.mjs (http block)

If you need me to access, download, or install something from one of these locations, you can either:

• Configure Actions setup steps to set up my environment, which run before the firewall is enabled
• Add the appropriate URLs or hosts to the custom allowlist in this repository's Copilot coding agent settings (admins only)