fix: C-01 WebRTC policy value, C-02 scoped taskkill, C-04 preflight race, E-11 socket timeout, E-27 ban test dedup, full audit doc

proxy_chain_manager/dns_leak.py

@@ -136,6 +136,7 @@ def flush_dns_cache() -> tuple[bool, str]:
 
 def _resolve_direct(hostname: str, timeout: float = 4.0) -> list[str]:
     """Resolve hostname using system DNS (direct, not through proxy)."""
+    _prev = socket.getdefaulttimeout()
     try:
         socket.setdefaulttimeout(timeout)
         infos = socket.getaddrinfo(hostname, None)
@@ -148,7 +149,7 @@ def _resolve_direct(hostname: str, timeout: float = 4.0) -> list[str]:
     except Exception:
         return []
     finally:
-        socket.setdefaulttimeout(None)
+        socket.setdefaulttimeout(_prev)
 
 
 def _resolve_via_proxy(hostname: str, proxy_url: str, timeout: float = 8.0) -> list[str]: