My basic question is whether the problems that needed solving about Twitter and other corporate social networks really have anything to do with software engineering at the end of the day.

Writing the code is honestly the easiest part in all probability. It is the other parts like community ownership, resiliency against corporate capture and human moderation that takes into consideration complex contexts etc… that are the truly hard parts and Bluesky really says almost nothing (at least worth trusting as more than words) new along those vital metrics (chiefly because it is an investor backed for-profit venture).

not the OP, but

i was going to point to the did:plc thing they made up and went with. but since the last time i looked, it looks like they support (and prefer) did:web, so that's sorted out.

the "wtf" i have is more to do with actually running a community with atproto. you need a central crawler service that knows about all the PDSes you want to be friends with (this is presumably why you need to sign up in their discord right now, they gotta tell their crawler to look at your PDS)

but i think the crawler has to grab the entire PDS for everyone it knows about? if you want a large community, it seems pretty resource-intensive since the ceiling is "infinity posts". bsky's open source code suggests they have chosen not to deal with this problem.

with most AP services (e.g. mastodon), you can prune the data and the only consequence is "you don't get full text search for super old posts received from other services that we pruned", so there are ways to limit the cost other than "limit the number of users in our community".

but this may just be an implementation detail and not an issue with atproto, e.g. git shallow clones are a thing, and the PDS is also storing a big merkel tree. i am not sure if the indexer relies on having the complete history or not (since you do need it for certain operations). bsky's own code just shrugging suggests maybe limiting it is challenging, i dunno.