checker: define Resolution verdict constants to make the collect/evaluate contract explicit

checker/collect.go

@@ -76,7 +76,7 @@ func (p *danglingProvider) Collect(ctx context.Context, opts sdk.CheckerOptions)
 				seen[key] = true
 				classifyExternal(&pt, zoneRegistrable)
 				if skipResolution {
-					pt.Resolution = "skipped"
+					pt.Resolution = ResolutionSkipped
 				} else {
 					pt.Resolution, pt.ResolutionDetail = resolveHost(ctx, pt.Target)
 				}
@@ -287,7 +287,7 @@ func classifyExternal(pt *Pointer, zoneRegistrable string) {
 func defaultResolveHost(ctx context.Context, target string) (verdict, detail string) {
 	target = strings.TrimSuffix(target, ".")
 	if target == "" {
-		return "skipped", "empty target"
+		return ResolutionSkipped, "empty target"
 	}
 	cctx, cancel := context.WithTimeout(ctx, resolverTimeout)
 	defer cancel()
@@ -295,25 +295,25 @@ func defaultResolveHost(ctx context.Context, target string) (verdict, detail str
 	ips, err := net.DefaultResolver.LookupHost(cctx, target)
 	if err == nil {
 		if len(ips) == 0 {
-			return "no_answer", ""
+			return ResolutionNoAnswer, ""
 		}
-		return "ok", ""
+		return ResolutionOK, ""
 	}
 
 	var dnsErr *net.DNSError
 	if errors.As(err, &dnsErr) {
 		switch {
 		case dnsErr.IsNotFound:
-			return "nxdomain", dnsErr.Err
+			return ResolutionNXDomain, dnsErr.Err
 		case dnsErr.IsTimeout:
-			return "timeout", dnsErr.Err
+			return ResolutionTimeout, dnsErr.Err
 		case strings.Contains(strings.ToLower(dnsErr.Err), "servfail"):
-			return "servfail", dnsErr.Err
+			return ResolutionServFail, dnsErr.Err
 		default:
-			return "error", dnsErr.Err
+			return ResolutionError, dnsErr.Err
 		}
 	}
-	return "error", err.Error()
+	return ResolutionError, err.Error()
 }
 
 // ownerFQDN returns the record owner FQDN, preferring the service's _domain field over subdomain+apex.