Every sandbox whose traffic is intercepted trusts the egress certificate: once a sandbox has any outbound handler, Cloudflare passes all its traffic through the runner Worker and re-signs HTTPS, so an open sandbox with only the abuse-report host intercepted got SELF_SIGNED_CERT_IN_CHAIN on every HTTPS request after the network guardrails were removed (before, g1t's own sandboxes were restricted, and restricted ones were given the certificate).