chore: initial draft of space spec

[Gozala]

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I think we need to add schema queries to this, but I suggest we lang this if it looks good and do that as a followup pr

[ubik2]

If we're using this to explain, it might be nice to align the two examples, so the transaction log from this matches what we showed above. On the other hand, that may make the captions too complex (the combined transaction setting Bob's name and Alice's age).

[ubik2]

Added some comments, but overall, it's a really useful doc.
I don't think there's any reason not to land it, unless you want to get more eyes in review first.
As far as schema queries goes, I don't think it's critical to include here, since that's built on top of this foundation.
The motivation for schema queries is somewhat specific to us, where we have logical entities that span multiple objects. The audience for this document is probably more interested in the causal chain and consistency aspects.
For the new classification logic, I think that's still likely to change, so I'm hesitant to publish it more broadly until it's more stable. For example, I chose application/label+json to attach my labels, but maybe there's a better name that makes more sense (or maybe we start storing schema objects instead).