Data Availability Failure

How it happens

A validity proof shows that a state transition was computed correctly, but it does not show that anyone else can see the data behind it. If an operator publishes proofs while withholding the underlying transactions, users cannot rebuild their balances, cannot construct a withdrawal, and in optimistic designs cannot construct a fraud proof at all. Systems differ in where they put the data: on the settlement chain as calldata or in blobs that are pruned after a retention window, on a separate data-availability network with its own validator set and sampling scheme, or with a permissioned committee that merely attests that data exists. Each choice moves the trust assumption somewhere, and the weakest link decides whether an exit is possible without the operator's cooperation.

What you can actually observe

Establish where data is posted, what the retention window is, and who is expected to archive it after that window closes. For committee-based designs, look at the number of members, the signing threshold, and whether members are independent entities. Where sampling is used, check whether light clients actually perform it in production or only in specification, and look for any documented drill in which a third party reconstructed state from published data alone.

Precedent

Plasma designs were largely set aside in favor of rollups because users could not be assured of obtaining the data required to exit if an operator withheld it.

What makes it more or less material

Relevant conditions are whether data goes to the settlement layer or elsewhere, the retention period, the size and independence of any committee, and whether an exit is possible using only public data.