chore: handle push of unchanged schema

ctl/ctl.go

@@ -2,6 +2,7 @@ package ctl
 
 import (
 	"context"
+	"fmt"
 	"net/http"
 	"net/url"
 
@@ -47,15 +48,19 @@ func List(apiKey, schemaRef, service string, schemasUrl url.URL) ([]*SubGraph, e
 	if err != nil {
 		return nil, err
 	}
-	subGraphs := make([]*SubGraph, len(response.SubGraphs))
-	for i, subGraph := range response.SubGraphs {
-		subGraphs[i] = &SubGraph{
-			Service:   subGraph.Service,
-			URL:       subGraph.Url,
-			WSUrl:     subGraph.WsUrl,
-			ChangedBy: subGraph.ChangedBy,
-			ChangedAt: subGraph.ChangedAt,
+	var subGraphs []*SubGraph
+	if s, ok := response.Supergraph.(*SubGraphsSupergraphSubGraphs); ok {
+		subGraphs = make([]*SubGraph, len(s.SubGraphs))
+		for i, subGraph := range s.SubGraphs {
+			subGraphs[i] = &SubGraph{
+				Service:   subGraph.Service,
+				URL:       subGraph.Url,
+				WSUrl:     subGraph.WsUrl,
+				ChangedBy: subGraph.ChangedBy,
+				ChangedAt: subGraph.ChangedAt,
+			}
 		}
+		return subGraphs, nil
 	}
-	return subGraphs, nil
+	return nil, fmt.Errorf("unexpected response type")
 }