Document encrypted group attachment format and grant lifecycle

src/dm/dm_media.c

@@ -25,6 +25,7 @@
 #include "../transport_layer/secure_channel.h"
 #include "../transport_layer/etcp.h"
 #include "../media_delivery/file_transfer.h"
+#include "../media_async/encrypted_file.h"
 
 enum dm_file_work { DM_FILE_PREPARE, DM_FILE_RECEIVE, DM_FILE_CUSTODY, DM_FILE_DELETE };
 struct dm_file_job;