feat: balance checker added

[0xHarbs]

🤖 Linear

Adding balance checker to the monorepo.

[Copilot]

Pull request overview

Adds a new Solidity utility contract under packages/contracts to query ERC20 balances (single + batch) and also returns the native (ETH) balance in the batch variant.

Changes:

• Introduces BalanceChecker contract with a single-token balance getter.
• Adds an overloaded batch balance getter that also appends native balance.

---

💡 Add Copilot custom instructions for smarter, more guided reviews. Learn how to get started.

[Copilot]

These two overloaded getTokenBalance functions can be awkward for off-chain consumers (ethers/web3) because calling an overloaded function often requires using the fully-qualified signature string. If this contract is intended for broad external consumption, consider renaming the array version to something like getTokenBalances (and/or clarifying whether native balance is included).

Suggested change

	function getTokenBalance(address[] memory _token, address _account) external view returns (uint256[] memory) {
	function getTokenBalances(address[] memory _token, address _account) external view returns (uint256[] memory) {

[Copilot]

A new intent contract is introduced without corresponding unit tests. The packages/contracts/test/unit/intent/ suite has coverage for other intent contracts; adding tests for both the single-token and multi-token/native-balance behaviors would help prevent regressions and clarify the intended return shape.

[Copilot]

The array overload of getTokenBalance allocates tokens.length + 1 and appends the native (ETH) balance at the end. Given the function name/signature, this is easy for callers to misinterpret and can lead to off-by-one mistakes (output length no longer matches the input token list). Consider renaming and/or changing the API so the return shape clearly reflects whether native balance is included and in what position.

Suggested change

	uint256[] memory balances = new uint256[](_token.length + 1);
	for (uint256 i = 0; i < _token.length; i++) {
	balances[i] = IERC20(_token[i]).balanceOf(_account);
	}
	balances[_token.length] = _account.balance;
	return balances;
	}
	uint256[] memory balances = new uint256[](_token.length);
	for (uint256 i = 0; i < _token.length; i++) {
	balances[i] = IERC20(_token[i]).balanceOf(_account);
	}
	return balances;
	}
	function getNativeBalance(address _account) external view returns (uint256) {
	return _account.balance;
	}

[Copilot]

getTokenBalance(address[] ...) takes the token array as memory even though the function is external. Using calldata here avoids an unnecessary copy and is the common pattern used elsewhere in this package for external array inputs.

Suggested change

	function getTokenBalance(address[] memory _token, address _account) external view returns (uint256[] memory) {
	function getTokenBalance(address[] calldata _token, address _account) external view returns (uint256[] memory) {

[Copilot]

Empty constructor is redundant here (no state initialization) and can be removed to reduce bytecode size and avoid implying there is construction logic.

Suggested change

constructor() {}

[Copilot]

Import formatting is inconsistent with the rest of the Solidity codebase, which uses no spaces inside the curly braces (e.g. import {IERC20} ...). This file currently uses import { IERC20 } ...; consider matching the existing style to keep forge fmt / lint output consistent.

Suggested change

	import { IERC20 } from '@openzeppelin/contracts/token/ERC20/IERC20.sol';
	import {IERC20} from '@openzeppelin/contracts/token/ERC20/IERC20.sol';