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/rules.md

@@ -235,6 +235,11 @@ nftables names (`@trusted_v4`). The importer makes raw rules from
 what it can't translate. It goes into the ruleset as written: add
 `counter` to it to count its packets.
 
+In shadow mode ([shadow.md](shadow.md)) a raw rule's final `drop` or
+`reject` becomes `accept`; a raw rule that does anything else to packets
+(NAT, `meta mark set`, `jump`, `notrack`, a verdict map…) is left out,
+with a warning (`shadow_raw_left_out`).
+
 ## Built-ins
 
 Housecarl adds the rules every firewall needs before yours. Each can be