URL Filter fails on macOS 27.2 beta: privacy-proxy failure on PIR status request

On macOS 27.2 beta 1/2 our URL filter never starts: the session loops starting -> stopping. The same build works on macOS 27.0 (26A428). Both our TestFlight and notarized standalone builds fail.

• Prefilter and PIR registration succeed.
• The PIR status request then fails: NWPath is satisfied, the connection is configured proxy fail closed, proxy strict fail closed, the proxy fails (event: proxy:children_failed), and the error is NSURLErrorDomain -1009 / POSIX 50 "Network is down" with _NSURLErrorPrivacyProxyFailureKey=true.
• NEMembershipCheckerErrorDomain Code=3 -> NEAgentURLFilterErrorDomain Code=3; the app sees serverSetupIncomplete.

The privacy-proxy allow-list entry is identical on macOS 27.0 and 27.2 beta (com.adguard). Disabling the VPN, rebooting, and recreating the URL filter configuration do not help.

Log excerpt:

neagent: updatePrefilterWithCompletionHandler - result 1
neagent: <NEPIRChecker> - Register with PIR Server (group <com.adguard.safari.AdGuard> ... PrivacyProxyFailOpen <0> ...) -> completed registration
ciphermld: [C3 ...] proxy fail closed, proxy strict fail closed
ciphermld: [C3.1.1 ... failed proxy (satisfied (Path is satisfied), interface: en0[802.11], ipv4, dns, uses wifi, flow divert agg: 2, LQM: good)] event: proxy:children_failed
ciphermld: queryStatus: NSURLErrorDomain -1009 / POSIX 50 "Network is down", _NSURLErrorPrivacyProxyFailureKey=true, NWPath=satisfied
neagent: Failed to startFilter <Error Domain=NEMembershipCheckerErrorDomain Code=3 "(null)">
nesessionmanager: NEURLFilterPlugin(com.adguard.safari.AdGuard[url-filter][inactive]): setStatus:error: - err Error Domain=NEAgentURLFilterErrorDomain Code=3

Filed as FB24933164.