Moves the_stream_agent_ignores_the_proxy_environment to crates/mind-body/tests/stream_proxy.rs, as control.rs carries its env-touching tests. It asserts through the public surface: with a proxy in the child's environment the stream's agent reaches its endpoint directly and follows no redirect, and a plain ureq agent in the same environment takes the proxy. No behaviour change.
Co-Authored-By: Claude Sonnet 5.5 <noreply@anthropic.com>
77ce0465ea