Because the `codex` process could contain sensitive information in
memory, such as API keys, we add logic so that when
`CODEX_SECURE_MODE=1` is specified, we avail ourselves of whatever the
operating system provides to restrict observability/tampering, which
includes:
- disabling `ptrace(2)`, so it is not possible to attach to the process
with a debugger, such as `gdb`
- disabling core dumps
Admittedly, a user with root privileges can defeat these safeguards.
For now, we only add support for this in the `codex` multitool, but we
may ultimately want to support this in some of the smaller CLIs that are
buildable out of our Cargo workspace.
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