fix(source/cloud-sql-admin): validate source instance for backup-run restore

RestoreBackup's BackupRun-ID path consumes sourceProject + sourceInstance, but the guard required sourceProject + targetInstance. targetInstance is already mandatory for the RestoreBackup API call, so an empty source_instance slipped through and a malformed RestoreBackupContext{InstanceId:""} was sent. Validate sourceInstance, matching the tool parameter and docs that mark both source fields required when backup_id is a BackupRun ID. Adds a regression test case.

Author: anxkhn

internal/sources/cloudsqladmin/cloud_sql_admin.go

@@ -412,7 +412,7 @@ func (s *Source) RestoreBackup(ctx context.Context, targetProject, targetInstanc
 	//    'projects/{project-id}/backups/{backup-uid}'. In this case, the Backup
 	//    field should be populated.
 	if backupRunID, err := strconv.ParseInt(backupID, 10, 64); err == nil {
-		if sourceProject == "" || targetInstance == "" {
+		if sourceProject == "" || sourceInstance == "" {
 			return nil, fmt.Errorf("source project and instance are required when restoring via backup ID")
 		}
 		request.RestoreBackupContext = &sqladmin.RestoreBackupContext{

tests/cloudsql/cloud_sql_restore_backup_test.go

@@ -186,6 +186,12 @@ func TestRestoreBackupToolEndpoints(t *testing.T) {
 			body:     `{"target_project": "p1", "target_instance": "instance-project-level", "backup_id": "12345"}`,
 			want:     `{"error":"error processing GCP request: source project and instance are required when restoring via backup ID"}`,
 		},
+		{
+			name:     "missing source instance with source project for standard backup",
+			toolName: "restore-backup",
+			body:     `{"target_project": "p1", "target_instance": "instance-project-level", "backup_id": "12345", "source_project": "p1"}`,
+			want:     `{"error":"error processing GCP request: source project and instance are required when restoring via backup ID"}`,
+		},
 		{
 			name:     "missing backup identifier",
 			toolName: "restore-backup",