fix: proxy detection behind pf redirects

[yangshun]

Summary

Fixes a false positive existing proxy check when /etc/pf.conf is modified.

Background

I wanted to access my sites without any port numbers, so I modifed my /etc/pf.conf and added this line

rdr pass on lo0 inet proto tcp from any to 127.0.0.1 port 80 -> 127.0.0.1 port 1355

After modifying it, I enabled pfctl so that I can access at my app at http://myapp.localhost, which gets routed to http://myapp.localhost:1355:

sudo pfctl -e

This worked fine. But after I stopped the portless proxy server, I could not start it again, and I get this error "Proxy failed to start (timed out)".

Things recovered after disabling pfctl:

sudo pfctl -d

I could start portless again like before.

My changes to /etc/pf.conf led portless to think that the proxy server is running when it isn't. I think this is a bug in portless.

Fix

• Add a listener-port response header so health checks can tell which local port actually accepted the request
• Tighten isProxyRunning() to reject PF/NAT redirect false positives when the probed port differs from the actual listener port
• Add regression coverage for redirected-port detection and proxy response headers

Testing

• pnpm --filter portless test
• pnpm --filter portless typecheck
• pnpm --filter portless build

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