fix(miniflare): bypass proxy for local inspector connections

[Zuckjet]

Fixes #8906

When users have proxy environment variables set (HTTP_PROXY, HTTPS_PROXY, etc.),
the local development server fails to start with a "TypeError: fetch failed" error.

Root cause

• Wrangler detects proxy environment variables and sets a global ProxyAgent
• Miniflare's InspectorProxyController makes a fetch request to 127.0.0.1
  to connect to the workerd inspector
• This local request incorrectly goes through the proxy, which typically
  cannot handle localhost addresses, causing the connection to fail

Solution

Modified InspectorProxyController.updateConnection() to use a dedicated
Agent for the local fetch request, bypassing the global proxy settings.
Local inspector connections should never be proxied.

---

• Tests
  • Tests included/updated
  • Tests not necessary because: Tested locally with proxy environment variables set
• Public documentation
  • Cloudflare docs PR(s):
  • Documentation not necessary because: This should be defalut behavior
• Wrangler V3 Backport
  • Wrangler PR:
  • Not necessary because: Not a patch change, not a Wrangler change

[changeset-bot]

🦋 Changeset detected

Latest commit: cd09cfe

The changes in this PR will be included in the next version bump.

Not sure what this means? Click here to learn what changesets are.

Click here if you're a maintainer who wants to add another changeset to this PR

[edmundhung]

Hi @Zuckjet, thanks for the contribution. I have a look of the issue and believe this is a side effect from wrangler proxy agent and so it's better handled in the wrangler side.

I have pushed a fix in #12516 and should be landed soon.