9c06ab2841
A Hetzner Storage Box drops an SFTP connection that carried a lot of data and then stayed quiet for a few minutes; files_external keeps using the dead client, on which every file looks missing. StorageBackend now checks the connection after a minute without requests, and replaces a connection that is dead after a failed request (once per request; put, move and delete are not repeated). SftpReadStream closes a connection it left in an unknown state. The verify cache refresh took more than 6 minutes on PostgreSQL for 27,547 packs, one autocommitted insert per pack: putMany()/replaceAll() write in one transaction. After a verify the cache holds the index files as they are, so a blob in two packs stays cached for both.