fix(cloud): remove retired relay code and DNS dependency

.changeset/remove-retired-relay.md

@@ -0,0 +1,5 @@
+---
+"ftw": patch
+---
+
+Remove the retired relay client and use FTW Cloud for the network route lookup that binds software identity. App sessions continue through the existing Cloud tunnel.

go/cmd/ftw/app_link.go

@@ -646,8 +646,8 @@ func goalRev(st loadpoint.State) uint32 {
 	return h.Sum32()
 }
 
-// startAppLink connects the box to the app relay when its loaded config leaves
-// the link enabled. Config defaults an omitted app_link section on.
+// startAppLink prepares app sessions for the FTW Cloud tunnel when enabled.
+// Config defaults an omitted app_link section on.
 //
 // It returns the enrollment identity whether or not the uplink runs, because
 // the QR code on the lid is minted from it and a box with the link switched

go/cmd/ftw/main.go

@@ -2383,7 +2383,7 @@ func main() {
 	}
 
 	// The FTW app's uplink. It speaks the app's own protocol end to end and
-	// reaches the box through a relay that holds no keys.
+	// reaches the box through the encrypted FTW Cloud tunnel.
 	appLinkWatchdog := time.Duration(cfg.Site.WatchdogTimeoutS) * time.Second
 	if appLinkWatchdog <= 0 {
 		appLinkWatchdog = 60 * time.Second
@@ -2410,7 +2410,7 @@ func main() {
 	case appLinkErr != nil:
 		slog.Warn("app link unavailable", "err", appLinkErr)
 	case appLinkEnabled:
-		slog.Info("app link connected", "relay", appuplink.Endpoint,
+		slog.Info("app link ready", "transport", "cloud",
 			"paired_devices", appEnroll.AuthorisedCount())
 	default:
 		slog.Info("app link disabled — set app_link.enabled to turn it on")