The budget in _sweep_agent_cache_under_pressure comes from the gateway's own
cgroup memory.high/memory.max, but read_anon_rss_mb() read /proc/self/status
RssAnon: only the main process. Every child in the unit (execute_code kernels,
terminal commands) is charged against the same limit, so a kernel at 4.7 GiB
pushed the unit to MemoryHigh while the valve saw <1.6 GiB and never fired;
systemd's stop then SIGKILLed the gateway mid-flush (the #80764 signature).
Under a capped cgroup v2, read own memory.stat `anon` (the same scope as the
budget); uncapped, or when the file is unreadable, keep the self reading.
_finite_limit is factored out of _cgroup_limit_bytes so the cap check and
the budget agree on what "unlimited" means.
Fixes#110549
7b44106174