The agent runs as redflag-agent user and cannot read /proc/[pid]/environ
from the logged-in user's session processes (owner-only permissions).
Without this, discoverSessionDisplay() finds nothing — screenshot fails
on Wayland because XDG_RUNTIME_DIR/WAYLAND_DISPLAY are never discovered.
- Installer: setcap cap_sys_ptrace=eip after placing the binary
- Helper (agent self-update): restore setcap after atomic replace,
since rename() creates a new inode and strips file capabilities
Non-fatal if setcap is unavailable — agent degrades gracefully,
just loses screenshot and per-process telemetry.
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