I’m aware he isn’t there now, but it bears remembering that he was there at the beginning when these goals were being shaped, and as we have seen with twitter there’s nothing to stop him coming back, even if nostr is his new best friend for now.

I read that posts on BlueSky are permanently stored in a blockchain,

So, this is complex and hard to find concrete information on, but:

1. Bluesky use a merkle tree based things. Don’t call em blockchain… that’s the sort of thing cryptocurrency boosters want so as to present their technologies are useful.
2. Posts are stored in a merkle search tree, but attachments are stored separately. Attached blobs (like images) can be (and are) deleted independently of the tree nodes which reference them.
3. The merkle trees are independent and can be modified without having to rewrite the whole history of every post on bluesky, because there isn’t one central official ledger of all posts.

From bluesky’s own (non technical) blurb on the subject,

it takes a bit longer for the text content of a post to be fully deleted in storage. The text content is stored in a non-readable form, but it is possible to query the data via the API. We will periodically perform back-end deletes to entirely wipe this data.

The merkle trees are per-user, which makes history-modifying operations like rebasing practical… this facility apparently landed last summer, eg. Intention to remove repository history. Flagging tree nodes as deleted, and then actually destroying them in a series of later operations (rebase, then garbage collection) would explain the front end respecting deletions but lower-level protocols showing older state for a little while.