My biggest concern is how we will solve an active synchronization of blobs. Currently it is user centric, i.e. a user or an app on behalf of a user can upload and duplicate blobs on multiple servers.

- 1. With current API blobs can be listed on a user basis. Compared to a nostr relay, where I  anyone can get a feed of events and publish them to any relay, the blossom server doesn't have a feed of new blobs.  It would be hard to duplicate content without a user (npub) focus. (still wondering if we need that).

- 2. I think we might need a way to check if a blob is on a server without downloading it and without doing a lookup on upstream servers. I'm thinking it may be useful to add HEAD /<sha256> to the spec for that.

- 3. We might need to solve a circular dependency problem in how the "download" from upstream servers work. If we have blossom servers pointing to each other in a circular way, pulling blobs from an upstream server might end up in an endless loop.