Node's built-in fetch (undici) ignores proxy environment variables, so
bl always connected directly and failed with ECONNRESET behind a VPN or
corporate proxy. Install an EnvHttpProxyAgent as the global dispatcher at
startup, but only when a proxy variable is actually set — behavior is
unchanged otherwise. Lowercase variables take precedence over uppercase
(curl convention) and NO_PROXY is honored.
Values are trimmed and passed explicitly to work around undici reading
env vars with ??, where an empty lowercase variable (https_proxy="")
masks a configured uppercase one. Invalid proxy URLs fail with a clear
usage error instead of a stack trace, and the ECONNRESET hint now
suggests exporting HTTPS_PROXY.
Tests are fully offline and need no credentials: unit tests cover env
parsing, and the e2e test runs a minimal probe (setupProxyFromEnv + a
bare fetch) against a .invalid host through a local CONNECT proxy to
verify traffic routes through the proxy, NO_PROXY is honored, no
dispatcher is installed when unset, and invalid values error clearly.
若麒