An aside:

On 27/10/2021 19:01, Ævar Arnfjörð Bjarmason wrote:

I don't think you can say "this bundle has no blobs". The
"prerequisites" hard map to the same thing you could put on a
"want/have" line during PACK negotiation.

I think we could/should fix that, i.e. we can 

bump the bundle format
version and have it encode some extended prerequisites/filter/shallow
etc information.

If the format is bumped, could we also include the
HEAD=<particular-branch> info within that format.
The `guess the HEAD` algorithm isn't ideal and shows up in user
questions every now and again.

 You'd then have a 1=1 match between the features of
git-upload-pack and what you can transfer via the bundle side-channel.

--
Philip