Adds docs/rfc/implemented/2026-06-19-real-api-e2e-ci.md covering the rationale
for running the real-API e2e suite in a separate secret-consuming workflow, the
fork/Dependabot/secret threat model, the residual exposure of the pull_request
trigger, and what changes when the repo goes public. Indexes it in the RFC
README.
Also adds a SECURITY comment on the pull_request trigger forbidding a switch to
pull_request_target (an untrusted-code-with-secrets leak vector, especially once
public), pointing at the RFC.
Tianyi Cui
27721f9f45