On Linux the three host probes of the build did nothing. available_ram returned None, so the lift started one worker per CPU whatever the memory and could run the machine out of it; keep_awake did nothing, so the machine could sleep in the middle of a build of 10 to 25 minutes; cpu_tag returned 'any', so the compile step's key ignored the processor and a game folder moved to a CPU without AVX2 kept its x86-64-v3 objects.
available_ram now reads MemAvailable from /proc/meminfo and, when the process runs under a cgroup v2 memory limit (its own or a parent's), caps it by memory.max less memory.current. keep_awake starts systemd-inhibit with a lock on sleep (not idle: the screen may still blank and lock, as with ES_SYSTEM_REQUIRED on Windows) around a cat that reads a pipe this process holds open, so the lock ends with the process even when it is killed; without systemd-inhibit it does nothing. cpu_tag reads the flags of /proc/cpuinfo and returns the digits the Windows branch returns for SSE4.2, AVX2 and AVX-512F, counting a feature only when every logical processor has it.
The compile key now holds the real tag instead of 'any', so an existing Linux build compiles once more. The compile --jobs defaults are unchanged. tests/host_probes_test.py covers the three probes over fake /proc and cgroup files and a fake systemd-inhibit.
Co-Authored-By: Claude Sonnet 5.5 <noreply@anthropic.com>
