Sandbox proxy fails with 502 Bad Gateway under sustained request load

Description

The sandbox proxy (running on localhost:52010) becomes unstable when handling multiple consecutive HTTP requests to allowed hosts, causing "Tunnel connection failed: 502 Bad Gateway" errors.

Reproduction Steps

1. Add a host to the sandbox network allowlist (e.g., via /sandbox)
2. Run a Python script that makes multiple consecutive API requests to that host using urllib.request
3. After approximately 5-10 rapid requests, subsequent requests fail with "502 Bad Gateway"
4. After ~2 seconds of inactivity, requests start working again

Observed Behavior

• First few requests succeed
• Proxy enters a "bad state" after sustained load
• All subsequent requests fail with: {"error": "Cannot connect: Tunnel connection failed: 502 Bad Gateway"}
• Proxy recovers after a brief pause (~2 seconds)

Expected Behavior

The sandbox proxy should handle consecutive requests to allowed hosts without failing.

Environment

• Claude Code version: 2.1.9
• Platform: macOS (Darwin 25.2.0)
• Python scripts using urllib.request (which respects HTTP_PROXY/HTTPS_PROXY environment variables set by the sandbox)

Workaround

Using dangerouslyDisableSandbox: true bypasses the proxy entirely and works reliably.

Additional Context

The proxy environment variables are set by Claude Code itself:

HTTP_PROXY=http://localhost:52010
HTTPS_PROXY=http://localhost:52010

The issue appears to be related to connection handling or rate limiting in the proxy, not the destination host (which is correctly allowlisted).