Object existence draft
The Condensation store protocol does not contain any function to check if an object exists.
A hypothetical exists function would take a hash and respond whether the object exists on the store or not. This information would not be verifiable by the client, however. The server may claim to have an object when it actually doesn't. Hence, the function would only be meaningful on trusted stores.
Note that this is in stark contrast to the object get function, which delivers the object as proof.
On trusted stores, checking for object existence is hardly useful for the client, as it is not enough to verify the integrity of the data. For the client, it is inevitable to download the whole tree for a full integrity check.