Blockchain-Grundlagen
Data availability: can the state be independently reconstructed?
A commitment identifies data; availability determines whether the required data can be obtained.
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A hash is not a download
A cryptographic commitment can bind an operator to a particular dataset without supplying that dataset to everybody who needs it. If users cannot obtain transaction data, reconstructing balances or checking an operator's assertions may become impossible despite the existence of a valid-looking commitment.
Availability mechanisms address that problem through publication, replication, sampling or additional committees, depending on the design. Each arrangement has assumptions about who retains data and what happens when some participants fail or withhold it.
Availability and archival history differ
Data being available during a protocol's verification window does not mean every node stores it forever. Long-term historical research can depend on archival services even when the protocol's immediate security requirements were satisfied. The retention model should be stated explicitly.
Ethereum blobs illustrate why temporary availability and permanent contract storage are different resources. Fault proofs and validity proofs use data in different ways, but neither makes it sensible to ignore where a user obtains the information needed for an independent exit.