fix(cas-redirection): Avoid returning URL when CAS is not valid (#2796)

Signed-off-by: Javier Rodriguez <javier@chainloop.dev>

Author: javirln

app/controlplane/internal/service/casredirect.go

@@ -1,5 +1,5 @@
 //
-// Copyright 2023 The Chainloop Authors.
+// Copyright 2023-2026 The Chainloop Authors.
 //
 // Licensed under the Apache License, Version 2.0 (the "License");
 // you may not use this file except in compliance with the License.
@@ -110,6 +110,11 @@ func (s *CASRedirectService) GetDownloadURL(ctx context.Context, req *pb.GetDown
 		return nil, kerrors.NotFound("not found", "CAS backend is inline")
 	}
 
+	// check if the backend is on a valid state, if not return an error
+	if backend.ValidationStatus != biz.CASBackendValidationOK {
+		return nil, pb.ErrorCasBackendErrorReasonInvalid("CAS Storage is in an invalid state and can't download artifacts, please fix it before attempting it again")
+	}
+
 	// Create an URL to download the artifact from the CAS backend
 	downloadBase, err := url.Parse(s.casServerConf.GetDownloadUrl())
 	if err != nil {