feat: decode contract method signature and args in /construction/parse

[andrew-lin-cb]

Motivation

/construction/parse omitted method_signature and method_args for contract-call transactions (there was even a //TODO: add logic for contract call parsing). Consumers that need to verify a transaction's intent — e.g. confirming a delegate(address) call targets the address the customer intended — had nothing decoded from the calldata to check against, so they fell back to the caller-supplied (self-declared) values.

That's a verification gap: a payload whose calldata targets address X could declare intended address Y and still pass validation, because nothing independently re-derived the destination from the signed bytes.

Solution

Decode the method signature and arguments directly from the transaction calldata and surface them in the parse response metadata, so they become a verified source of truth rather than an echo of the declaration.

• Allowlist of signatures, not an ABI download. A 4-byte selector is a one-way keccak hash of the signature and cannot be reversed, so decoding is only possible against known signatures. A new RosettaConfig.SupportedContractMethods []string lets each chain declare the method signatures (e.g. "delegate(address)") it wants decoded — mirroring the existing TokenWhiteList pattern.
• Exact inverse of the encoder. The decoder (ParseContractCallData) inverts ConstructContractCallDataGeneric, emitting args in the same string form the encoder accepts, so a decoded (method_signature, method_args) pair round-trips back to identical calldata (verified across address / uint / int / bool / bytes / bytesN / array types).

Behavior: fail-open, never blocks a parse

/construction/parse never fails or blocks a request because of contract-call decoding:

• No matching method in the allowlist → request still succeeds (200); method_signature/method_args are simply omitted (omitempty). For any unmatched call the endpoint behaves byte-for-byte as it did before this PR.
• Matched but undecodable calldata → logs and omits the fields, request still succeeds (no 500).
• The only "closed" aspect is on the data, not the request: when nothing matches, the SDK omits the fields rather than emitting caller-supplied/unverified values, so downstream verifiers get verified data or nothing — never a spoofable echo. With an empty allowlist the output is unchanged, so this is fully backward compatible.

Safety around misconfiguration

• Startup validation. ValidateSupportedContractMethods lets a chain validate its configured allowlist at boot (well-formedness + valid, decodable ABI arg types) so misconfiguration fails loudly rather than at request time.
• Tuple/struct args are rejected explicitly (rather than silently decoding to the wrong or empty args), keeping decoded output a faithful, round-trippable representation of the calldata.

Scope

This PR only exposes the capability in the SDK. It does not turn decoding on for any chain: the SupportedContractMethods allowlist is populated per chain in the chain-specific implementation repos (e.g. rosetta-zksync), which will also opt in and call ValidateSupportedContractMethods at startup. With no list configured, behavior is unchanged.

Tests

Unit tests for MatchMethodSignature, ParseContractCallData (round-trip), tuple rejection, and ValidateSupportedContractMethods, plus /construction/parse tests covering a supported method decoding from calldata, an unsupported method emitting no method fields, and the request-time fail-open (matched-but-undecodable) path. go build ./..., go vet, and the construction suite pass.

[cb-heimdall]

✅ Heimdall Review Status

Requirement	Status	More Info
Reviews	✅ 1/1	Denominator calculation Show calculation 1 if user is bot 0 1 if user is external 0 2 if repo is sensitive 0 From .codeflow.yml 1 Additional review requirements Show calculation Max 0 0 From CODEOWNERS 0 Global minimum 0 Max 1 1 1 if commit is unverified 1 Sum 2

[potterbm-cb]

For posterity: looks like the github actions are broken at the moment. Andrew ran the checks locally and they passed so I'm merging this without CI running in GHA