The 1/2/3-user question is answered: stay at 2 (left4me + l4d2-sandbox).
The defenses that motivated a 3-user split (cross-uid ptrace,
cross-server contamination, web-side reach into gameserver state,
DB/env exposure to srcds) are closed by the systemd hardening
composition: PrivateUsers + PrivatePIDs + TemporaryFileSystem +
SystemCallFilter=~@debug + empty CapabilityBoundingSet.
The residual filesystem-ACL surface (mode 0640 root:left4me on DB and
web.env) is noted as a separate concern — covered for the current
deployment shape, revisit if shape changes.
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
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