Blob TTL

[afck]

Blobs should have a time-to-live (TTL). Even with a proof of their existence, validators will not accept using those blobs again after they have expired—except if they are re-published (and paid for) with a later TTL.

Since every proof of existence must convey the TTL, oracle responses must contain it, too, in addition to the blob ID itself.

(If the validators see the same blob with different TTLs, the block execution will fail because the oracle responses won't agree. Maybe that's not a problem: The client should just upload a proof of the later TTL to all validators to update them, and then retry.)

Blobs with TTL cannot be used in fast blocks even if they have been used on the same chain before. (Or we could allow them, and the client needs to be extremely careful, i.e. refuse to propose a fast block using a blob with a TTL lower than a few days.)