Shadow mode: Housecarl beside the firewall in force, changing nothing

shadow.enabled in housecarl.yaml loads Housecarl's ruleset so that it
blocks, rejects and translates nothing: drops and rejects count and
accept (an accept only ends Housecarl's chain), policies accept and log
what they would drop, NAT only counts, MSS clamping and the flowtable
are left out, and raw rules that do more than accept, drop or reject are
left out with a warning. Comments mark what would happen ([would drop]).
Filter chains run after the other firewall's (+10) or before (-10); NAT
chains always first. Every change is checked by nftables in both forms.
No probation; takeovers and closing connections are refused. The boot
fallback filters nothing. internal/tablewatch puts the table back after
a flush ruleset. Mode in status, healthz, whoami, the web UI, the log
and the tracer; hc ruleset --enforcing. docs/shadow.md.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

docs/validation.md

@@ -132,3 +132,8 @@ configuration: the dashboard and `hc status` show them.
 | `nftables_service` | warning, *host* | Debian's `nftables.service` is enabled: at boot it loads `/etc/nftables.conf`, and stopping or restarting it runs `nft flush ruleset`, deleting Housecarl's table too. Disable it with `systemctl disable nftables` (without `--now`) |
 | `conntrack_full` | warning, *host* | the connection tracking table is over 80% full; once it is full, the kernel drops new connections. Raise `net.netfilter.nf_conntrack_max`, or find what opens so many ([stats.md](stats.md#warnings)) |
 | `takeover_pending` | warning, *host* | the table you imported from is still in force beside Housecarl's, so a packet must get past both; `hc takeover TABLE` deletes it once Housecarl's rules are right |
+| `shadow_unprotected` | warning, *host* | shadow mode, and no other table has a filter chain on the input hook: Housecarl's ruleset blocks nothing, and nothing else protects the machine. Load your firewall, or leave shadow mode ([shadow.md](shadow.md)) |
+| `shadow_raw_left_out` | warning, *host* | shadow mode leaves this raw rule out: it does more to packets than accept, drop or reject (NAT, setting a mark or field, a jump, a verdict map…). Its hits aren't counted, and the rules after it see what it would have taken ([shadow.md](shadow.md#what-changes-in-the-ruleset)) |
+
+In shadow mode `nftables_service` and `takeover_pending` aren't raised:
+another firewall beside Housecarl is the point there.