Go toolchain cmd/go CVE-2026-39819

Upgrade Go toolchain to version 1.26.3 or later (preferred) or 1.25.10 or later for users still on the 1.25 release branch. The patch is available from the official Go downloads at https://go.dev/dl/ and is confirmed in the Go security advisory at https://groups.google.com/g/golang-announce/c/qcCIEXso47M. No workarounds are available short of avoiding use of the 'go bug' command. Compensating controls in high-risk environments (shared build systems, multi-tenant CI/CD) include restricting write access to the system temp directory via filesystem permissions or SELinux/AppArmor policies, isolating build processes in separate containers or VMs with private temp directories, and using mount options (noexec, nodev, nosuid) on tmpfs mounts. These controls have minimal performance impact but may complicate legitimate system administration tasks.