Counters: forget the totals of objects that no longer exist

hc counters kept listing the objects of a configuration replaced since
housecarld started (an import with --replace gives every object a new
ID) beside the current ones. Disabled objects, built-ins and policies
keep their totals.

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

internal/nft/nft_test.go

@@ -6,6 +6,7 @@ import (
 	"os"
 	"os/exec"
 	"path/filepath"
+	"sort"
 	"strings"
 	"testing"
 
@@ -437,3 +438,26 @@ func TestShadowInContainer(t *testing.T) {
 		t.Errorf("the shadow fallback isn't recognised: %+v %v", tb, err)
 	}
 }
+
+// TestPruneCounters: the totals of objects gone (an import with --replace
+// gives every object a new ID) are forgotten; built-ins, policies and
+// disabled objects keep theirs.
+func TestPruneCounters(t *testing.T) {
+	base := map[string]Counter{}
+	for _, m := range []string{"r1", "r2", "r3", "f4", "f4-hairpin", "f4-6", "f5-hairpin", "s6", "d7", "d8", "b-established", "p-input", "fallback-input"} {
+		base[m] = Counter{Packets: 1}
+	}
+	st := model.NewState()
+	st.Rules = []*model.Rule{{ID: 1}, {ID: 3, Disabled: true}}
+	st.Forwards = []*model.PortForward{{ID: 4}}
+	st.Redirects = []*model.Redirect{{ID: 8}}
+	pruneCounters(base, st)
+	var got []string
+	for m := range base {
+		got = append(got, m)
+	}
+	sort.Strings(got)
+	if strings.Join(got, " ") != "b-established d8 f4 f4-6 f4-hairpin fallback-input p-input r1 r3" {
+		t.Errorf("kept %v", got)
+	}
+}