Supersedes the evidence grade in "Agent CLI Changelog Delta (Day 257 scan)". Observed 2026-11-12 with two 127.0.0.1 stubs (A answers 307 to B on another port) and a canary key, yoyo 4ae43f30 / yoagent 0.27.7 / reqwest 0.13.4: with --provider anthropic, stub B received x-api-key=canary-not-a-key plus the full ~10.5KB request body on all 6 retry attempts. With --provider custom (bearer auth) B received authorization=None (reqwest strips it cross-origin) but still the full body. So x-api-key/api-key providers leak key and prompt on a cross-origin 307; bearer providers leak the prompt only. Method: recording stubs, never a real host.