Stream the delegation check's queries too

Every DNS query the name server checks send is now reported from
exchangeHostPort as a dig command line with a short answer (addresses,
referral, DS, NXDOMAIN) and its round-trip time; the serials check's SOA
queries keep their own events with the server's result. The delegation
check streams with ?stream=1 like /serials, and the Name servers tab
shows its queries as they happen, keeps its result and follows a running
check when you come back.

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

internal/nscheck/nscheck_test.go

@@ -6,6 +6,7 @@ import (
 	"net/netip"
 	"strconv"
 	"strings"
+	"sync"
 	"testing"
 	"time"
 
@@ -307,3 +308,64 @@ func TestDelegationDS(t *testing.T) {
 		}
 	}
 }
+
+// TestWatch: with Watch set, every query is reported as it starts and
+// ends, as a dig command line with a summary of the answer.
+func TestWatch(t *testing.T) {
+	port, res := internet(t, func(q dns.Question) *dns.Msg {
+		m := new(dns.Msg)
+		if q.Qtype == dns.TypeNS && q.Name == "adbraun.lol." {
+			m.Ns = []dns.RR{rr("adbraun.lol. 3600 IN NS ns1.adbraun.lol.")}
+			m.Extra = []dns.RR{rr("ns1.adbraun.lol. 3600 IN A 127.0.0.12")}
+		}
+		return m
+	})
+	var mu sync.Mutex
+	var events []Event
+	c := checker(port, res)
+	c.Watch = func(e Event) {
+		mu.Lock()
+		events = append(events, e)
+		mu.Unlock()
+	}
+	ref := uint32(7)
+	c.Delegation(context.Background(), "adbraun.lol.", []string{"ns1.adbraun.lol."}, map[string][]string{"ns1.adbraun.lol.": {"127.0.0.12"}}, &ref, nil)
+	open := map[int64]string{}
+	var queries, answers []string
+	for _, e := range events {
+		switch e.Kind {
+		case "start":
+			if !strings.HasPrefix(e.Query, "dig @") {
+				t.Errorf("query %q", e.Query)
+			}
+			open[e.ID] = e.Query
+			queries = append(queries, e.Query)
+		case "end":
+			q, ok := open[e.ID]
+			if !ok {
+				t.Errorf("end without start: %+v", e)
+			}
+			delete(open, e.ID)
+			a := e.Answer + e.Error
+			if e.Result != nil {
+				a = e.Result.Status
+			}
+			answers = append(answers, q+" => "+a)
+		}
+	}
+	if len(open) != 0 {
+		t.Errorf("never ended: %v", open)
+	}
+	all := strings.Join(answers, "\n")
+	for _, want := range []string{
+		" adbraun.lol. NS +norec => referral to ns1.adbraun.lol.",        // asking a parent server
+		"@127.0.0.12 -p " + port + " adbraun.lol. SOA +norec => in_sync", // asking the delegated server
+	} {
+		if !strings.Contains(all, want) {
+			t.Errorf("no %q in\n%s", want, all)
+		}
+	}
+	if len(queries) < 4 {
+		t.Errorf("only %d queries:\n%s", len(queries), all)
+	}
+}