feat: gate chain-specific host functions to the emulated chain

[robrigo]

Why

wax-vert registers verify_rsa_sha256_sig for every Blockchain. It exists on WAX and not on EOS, Jungle4 or Vaulta, so a contract importing it passed the harness and would fail to load on those chains. The harness was more permissive than three of the four Antelope chains these contracts deploy to, which is a class of false-green: a contract calling a WAX-only host function looks tested when it cannot deploy.

What

Host functions unique to a chain are withheld unless the emulated chain provides them. A Blockchain is generic Antelope by default and exposes none; new Blockchain({ chain: 'wax' }) adds the WAX set. The VM deletes any withheld function from its env imports before instantiating, so a contract importing one fails to instantiate under the wrong chain, mirroring how setcode rejects it. That is a load-time failure, which is faithful to where the real chain rejects it.

The set is declared in CHAIN_SPECIFIC_HOST_FUNCTIONS, keyed by chain. Modeling a new chain-specific function is one map entry, and it is then gated everywhere automatically.

Validation

35 tests pass (31 prior plus 4 for the gate). The two existing RSA tests now run against a wax blockchain. New tests assert verify_rsa_sha256_sig is absent by default, present under wax, absent under an unknown chain name, and that withholding it leaves shared host functions like recover_key intact. Verified directly that a default VM exposes undefined for it while a wax VM exposes a function.

Version 2.2.0: this adds behavior over the 2.1.1 base and gives the fork its own version line rather than sharing upstream's.

[Copilot]

Pull request overview

This PR tightens VeRT’s Antelope host-function parity by gating chain-specific host functions so contracts that import a function unsupported by the emulated chain fail at instantiation time (mirroring real setcode behavior), eliminating false-green test results across different Antelope chains.

Changes:

• Add a chain selector to Blockchain and define per-chain host-function availability via CHAIN_SPECIFIC_HOST_FUNCTIONS.
• In VM, remove (withhold) all chain-specific host functions from imports.env unless enabled for the selected chain.
• Update and extend tests/docs/examples to validate and demonstrate the new chain-specific gating; bump version to 2.2.0.

Reviewed changes

Copilot reviewed 6 out of 6 changed files in this pull request and generated no comments.

Show a summary per file

File	Description
src/antelope/vm.ts	Withholds chain-specific host functions from WASM imports based on the emulated chain.
src/antelope/blockchain.ts	Adds chain option and exposes chain-specific host-function sets (enabled + union).
src/antelope/tests/vm.spec.ts	Updates RSA tests to run under wax and adds gating assertions for default/wax/unknown chains.
examples/rsa/rsa.spec.ts	Uses new Blockchain({ chain: 'wax' }) so RSA example matches WAX host-function availability.
README.md	Documents the new per-chain host-function behavior and how to select a chain.
package.json	Bumps package version to 2.2.0.

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