Feature: OOM killer protection similar to sshd

I initially opened this as part of amaonlinux, but it makes more sense in this project:

When the system is experiencing memory pressure, I've seen many times that ssm-agent gets killed by the OOM killer. This makes it hard to debug the situation if ssm-agent being killed results in being unable to log in and observe the situation.

I'd like ssm-agent to be run with the same OOM killer protections that sshd applies to it's own process (oom score adjustment -1000).

Alternatives would be to stop using SSM for login and switch to SSH, but this puts additional overhead on us, administering user accounts and ssh keys. SSM session manager is a useful feature that would really benefit from added efforts to increase stability.

This old bug https://bugzilla.redhat.com/show_bug.cgi?id=1010429#c0 contains some details about how it used to work with sshd - especially making sure that user processes spawned by the "protected" server don't inherit the strict protection of oom_score_adj -1000.

Start by locating where ssm-agent launches its main process and how it handles process attributes, then review the referenced Red Hat bug for the sshd behavior. Confirm how OOM protection should apply to the agent without being inherited by user processes; done means the agent remains protected under memory pressure while spawned sessions retain normal OOM handling.

Written by the indexing model from the issue text.