ultra-v0.6.8 C4 (capture only): site-src/install.sh.tmpl unconditionally unsets the proxy and CA-bundle variables (HTTPS_PROXY, ALL_PROXY, CURL_CA_BUNDLE, SSL_CERT_FILE, SSL_CERT_DIR, CURL_HOME) before any fetch. The lockdown IS the GHSA-x4v8-rxvx-8v89 fix and hooks/bootstrap.sh mirrors it, so it is deliberate; the cost is that a host whose curl finds its CA bundle only through SSL_CERT_FILE (NixOS, minimal containers, custom OpenSSL) or a network reachable only through HTTPS_PROXY cannot install, and the generic could-not-download message does not say why. The review proposes an explicit escape such as ABCD_INSTALL_KEEP_ENV=1; the objection is that an environment-variable opt-out reopens the very vector the lockdown closes (the poisoned environment sets the escape too). Whether to trade the lockdown for those users is a product decision, not a code fix. The purely diagnostic part — naming the ignored variables in the failure message — does not weaken the lockdown.

ultra-v0.6.8 C4 (capture only): site-src/install.sh.tmpl unconditionally unsets the proxy and CA-bundle variables (HTTPS_PROXY, ALL_PROXY, CURL_CA_BUNDLE, SSL_CERT_FILE, SSL_CERT_DIR, CURL_HOME) before any fetch. The lockdown IS the GHSA-x4v8-rxvx-8v89 fix and hooks/bootstrap.sh mirrors it, so it is deliberate; the cost is that a host whose curl finds its CA bundle only through SSL_CERT_FILE (NixOS, minimal containers, custom OpenSSL) or a network reachable only through HTTPS_PROXY cannot install, and the generic could-not-download message does not say why. The review proposes an explicit escape such as ABCD_INSTALL_KEEP_ENV=1; the objection is that an environment-variable opt-out reopens the very vector the lockdown closes (the poisoned environment sets the escape too). Whether to trade the lockdown for those users is a product decision, not a code fix. The purely diagnostic part — naming the ignored variables in the failure message — does not weaken the lockdown.

Remedy grounds (2026-09-29)

• The objection to ABCD_INSTALL_KEEP_ENV=1 is that a poisoned environment sets it too; an argument the person types is not ambient state, which answers it. rustup and curl both read proxies from the environment by default: https://rust-lang.github.io/rustup/network-proxies.html and https://everything.curl.dev/usingcurl/proxies/env.html (consulted 2026-09-29), the behaviour GHSA-x4v8-rxvx-8v89 had to close.
• Rejected: the environment-variable escape the review proposed, for the reason above.