One-view tokens: local records in linked zones, zone lookup, view list

A token for one view of a linked zone (an ACME token for external)
couldn't add records: a new record was shared and reached the other
view. A new name and type is now local when the user may not change it
in the other views. A zone name in several views resolves to the only
one the user can see, and the error no longer names views they can't.
GET /views lists the views a user sees zones in (name, colour, count;
limited) without views:read.

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

internal/engine/linked.go

@@ -456,12 +456,30 @@ func (x *expander) unlinkOps(m *model.Zone, summary string) []model.Op {
 
 // localFor works out whether a new record (or set) in zone z is local:
 // as asked, or like the records of the same name and type already there.
+// A new name and type is shared, unless the principal may not change it
+// in every linked view (an ACME token for the external view only): then
+// it is local to z's view, which is all they may change.
 func (x *expander) localFor(z *model.Zone, name, typ string, want *bool) (bool, error) {
-	has := x.st.HasLocal(z.ID, name, typ)
-	if want == nil {
-		return has, nil
+	if want != nil {
+		return *want, nil
 	}
-	return *want, nil
+	if x.st.HasLocal(z.ID, name, typ) {
+		return true, nil
+	}
+	if len(x.st.SharedRecords(z.ID, name, typ)) > 0 {
+		return false, nil
+	}
+	var not []string
+	for _, o := range x.st.LinkedWith(z) {
+		if !x.p.Can(recordAction(x.st, o, name, typ, true)) {
+			not = append(not, x.st.ViewName(o))
+		}
+	}
+	if len(not) > 0 {
+		x.warnings = append(x.warnings, fmt.Sprintf("%s %s is local to view %s: you may not change it in %s", dnsname.Display(name), typ, x.st.ViewName(z), strings.Join(not, ", ")))
+		return true, nil
+	}
+	return false, nil
 }
 
 // shareAllOps returns the operations that start a link with zone z: it