fix: cis490-msfrpcd unit crashes with EROFS on /root/.msf4 (ProtectHome=true)

msfrpcd tries to mkdir ~/.msf4/ for its module cache and logs. The
cis490-msfrpcd.service unit sets ProtectHome=true, which makes /root
inaccessible (EROFS), so msfrpcd exits immediately on first start.

Fix: add Environment=HOME=/var/lib/cis490/msf4 to the unit template
and ReadWritePaths=/var/lib/cis490, and pre-create the msf4 dir in the
install script so msfrpcd can write its state there instead. ProtectHome
is preserved because /root is now never touched.

Closes spectral/CIS490#16

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

scripts/install-msfrpcd.sh

@@ -103,6 +103,10 @@ fi
 
 # --- 3. systemd unit ----------------------------------------------------
 log "installing systemd unit"
+# msfrpcd writes ~/.msf4/ for module cache and logs. ProtectHome=true in
+# the unit makes /root inaccessible, so redirect HOME to a writable path
+# under /var/lib/cis490/. Pre-create so msfrpcd doesn't race mkdir.
+install -d -m 0755 -o root -g root /var/lib/cis490/msf4
 cat > "$UNIT" <<EOF
 [Unit]
 Description=CIS490 — Metasploit RPC daemon (loopback only)
@@ -119,6 +123,7 @@ EnvironmentFile=$ENV_FILE
 #   -a <ip>   bind address (loopback only — Tier-3 driver runs locally)
 #   -p <port> port
 #   -f        foreground (no daemonization, so systemd manages PID)
+Environment=HOME=/var/lib/cis490/msf4
 ExecStart=/usr/bin/env msfrpcd -P \${MSFRPC_PASSWORD} -U \${MSFRPC_USER} -a 127.0.0.1 -p \${MSFRPC_PORT} -f
 Restart=on-failure
 RestartSec=5
@@ -126,6 +131,7 @@ NoNewPrivileges=true
 PrivateTmp=true
 ProtectSystem=full
 ProtectHome=true
+ReadWritePaths=/var/lib/cis490
 
 [Install]
 WantedBy=multi-user.target