Reopened and merged on the owner's call (2026-10-10). Combines with #15886 (already on the tip): keeps its secret stripping for /api/providers/client, adds the hard-gate for that route, and replaces the IPv4-only MITM bind with the dual-stack listener + loopback peer guard (the DNS spoof also maps hosts to ::1). The pinned listen test now asserts the guard is installed before listen(). MITM + authz suites 320/320, eslint clean. Warning: base-red inherited: #15306.