feat: accept foreign tx validation requests on contract

[DSharifi]

closes #2801

[claude]

Code Review

Minor issue found:

• Mislabeled test case in crates/near-mpc-contract-interface/src/types/foreign_chain.rs: The new test case is labeled #[case::bnb(...) but it tests ForeignChainRpcRequest::Arbitrum. Should be #[case::arbitrum(...).

Otherwise the change is straightforward — adding an Arbitrum variant to ForeignChainRpcRequest with proper test coverage across sandbox tests, ABI snapshot, and unit tests. No logic, safety, or compatibility concerns.

✅ Approved (with nit above)

[gilcu3]

Thank you!

[gilcu3]

side comment: I wonder if we need to test each chain separately here. These tests are unfortunately getting a noticeable time inside the sandbox tests (just my experience running them locally sometimes). If the behavior in the contract is actually the same for all chains, maybe we could just test one, or use some mechanism (trait?) to ensure that testing one is enough

[DSharifi]

I wouldn't want to lose test coverage. But we could instead collapse them all to one test case, and run requests against all of them in one test similar to what @anodar did with the e2e tests

mpc/crates/e2e-tests/tests/foreign_chain_tx_validation.rs

Lines 369 to 389 in 9c8acca

	async fn verify_foreign_transaction__should_sign_all_supported_chains() {
	// Given — 2-node cluster with Bitcoin, Abstract, BNB, Base, and Starknet configured
	let env = setup_foreign_tx_cluster()
	.await
	.expect("setup_foreign_tx_cluster failed");
	// When/Then — all configured chains produce valid signed responses
	verify_bitcoin(&env)
	.await
	.expect("bitcoin verification failed");
	verify_abstract(&env)
	.await
	.expect("abstract verification failed");
	verify_bnb(&env).await.expect("bnb verification failed");
	verify_base(&env).await.expect("base verification failed");
	verify_starknet(&env)
	.await
	.expect("starknet verification failed");
	verify_arbitrum(&env)
	.await
	.expect("arbitrum verification failed");

[gilcu3]

yeah that would also fix the problem indeed

[Copilot]

Pull request overview

Adds Arbitrum support to the NEAR MPC contract “foreign tx validation request” surface by extending the contract interface DTOs and updating sandbox/ABI tests accordingly (closes #2801).

Changes:

• Extend ForeignChainRpcRequest with a new Arbitrum(EvmRpcRequest) variant and map it to ForeignChain::Arbitrum.
• Update the ABI snapshot to reflect the new request variant shape.
• Add Arbitrum coverage to sandbox tests (including a new arbitrum_evm_request() helper) and to the DTO unit test cases.

Reviewed changes

Copilot reviewed 4 out of 4 changed files in this pull request and generated no comments.

File	Description
crates/near-mpc-contract-interface/src/types/foreign_chain.rs	Adds Arbitrum to ForeignChainRpcRequest and updates chain() + tests.
crates/contract/tests/snapshots/abi__abi_has_not_changed.snap	Updates ABI snapshot to include the new Arbitrum request variant schema.
crates/contract/tests/sandbox/foreign_chain_request.rs	Expands sandbox foreign-tx request tests to include an Arbitrum case.
crates/contract/tests/sandbox/common.rs	Adds arbitrum_evm_request() test helper for Arbitrum requests.

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