Fixed: disappearing profile pictures and attachments

We fixed a bug that could make a profile picture (and, in rarer cases, an attachment) stop loading and show a broken-image placeholder after about a week.

• What went wrong. A nightly job that reclaims unused files in storage was not aware of profile-picture files, so it treated them as unused and deleted them once they were a few days old.
• The fix. The cleanup job now recognises profile pictures and leaves them alone.
• So it can't happen again. The job now refuses to run if it would delete an unusually large number of files at once, and records exactly what it removes.

If a picture of yours went missing, re-uploading it will set it right. Recently affected files can also be restored from backups; contact support if you need a hand.