CVE-2026-61670: microsandbox: Secret values exposed in world-readable process arguments

When the SDK spawns a sandbox, the msb sandbox child process receives the full network configuration as an inline --network-config <json> command-line argument, and any per-sandbox environment as repeated --env KEY=VALUE arguments. On Linux a process’s arguments are world-readable via /proc/<pid>/cmdline, and on both Linux and macOS they are visible to other local processes via ps. Because the network configuration carries the real secret values used for host-side secret substitution, any unprivileged local user (or any process running as a different user on the same host) can read those secrets directly out of the process listing for as long as the sandbox is running. This defeats the “secrets that can’t leak” guarantee for the host side of the boundary.