docs: backasset is deprecated in v2 and always fails

[robrigo]

The v2 contract makes backasset fail unconditionally:

ACTION atomicassets::backasset(...) {
    check(false, "Native backing has been deprecated on the AtomicAssets Contract");
}

Two documents still described it as working, and both are the ones an integrator reads first.

README

The feature list advertised backing as current, promising assets "a guaranteed intrinsic value". It now says the action fails on v2, and states what is unaffected: burning an asset still releases tokens backed before the upgrade, and withdraw still works. That reassurance matters because holders of already-backed assets would otherwise have no way to tell whether their value was stranded.

Ricardian clause

resource/atomicassets.contracts.md still titled the clause "Backs an asset with tokens" and described a successful backing, including "The tokens backed to this asset can be retreived by burning the asset". It now says native backing is deprecated, the action always fails, no tokens move, and pre-v2 backed assets still release on burn.

Why this is worth doing now rather than at deploy

backasset is in live use. On WAX mainnet there are more than 10,000 recorded calls, roughly 100 in the last four days across 18 distinct accounts, the most recent yesterday. Those callers break the moment the v2 upgrade executes, and until then the documentation tells them the feature is supported. EOS has no calls at all.

The change is invisible to an ABI diff, since the action is still present with an unchanged struct, so documentation is the only place it surfaces.

Note on scope

This does not change the ABI. Ricardian text is not currently embedded in the AtomicAssets ABI at all: the shipped atomicassets.abi has ricardian_clauses: [] and every action carries ricardian_contract: "", because the Makefile omits the -R./resource flag its atomicmarket counterpart passes. That gap is real and worth its own change, but it cannot ride v2.0.0 since adding the flag changes abiSha256 and the release is pinned by hash. Raised separately.

[Copilot]

Pull request overview

Updates AtomicAssets v2 integrator-facing documentation to reflect that the backasset action is deprecated and fails unconditionally, while clarifying what remains functional for previously backed assets.

Changes:

• Update README feature list to mark fungible-token backing as disabled in v2 and describe unaffected flows (burn + withdraw).
• Update backasset Ricardian clause to state the action always fails in v2 and that pre-v2 backed assets are unaffected.

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 3 comments.

File	Description
resource/atomicassets.contracts.md	Updates backasset Ricardian clause title/summary/description to reflect v2 deprecation and failure behavior.
README.md	Adjusts the feature list entry to note backasset is disabled in v2 and summarizes what still works for already-backed assets.

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