[PR #38] p2: vBNB native collateral path has no test — no regression guard for issue #121 fix

[obchain]

Summary

Issue #121 documents that the vBNB collateral redemption path is broken: IVToken(collateralVToken).redeem() returns native BNB (not ERC-20), so IERC20(collateralToken).balanceOf(address(this)) returns 0 and the swap swaps nothing. The fix requires a WBNB wrap step after redeem.

This test PR adds no test — not even a mocked unit test — that exercises the vBNB collateral path. Once #121 is fixed, there will be no regression guard ensuring the fix remains correct. Given that vBNB (0xA07c5b74C9B40447a954e1466938b865b6BBea36) is one of the most-liquidated collateral assets on Venus, this is a high-frequency production path.

Location

contracts/test/CharonLiquidator.t.sol — no test parameterizes collateralVToken = vBNB_ADDRESS or simulates a native BNB return from redeem

Fix

Add a mocked unit test with:

1. A stub collateral vToken whose redeem() sends native BNB to address(liquidator) (via vm.deal + transfer).
2. A stub WBNB that accepts native BNB deposits and mints ERC-20.
3. Assert that the swap router receives WBNB, not zero, and the liquidation succeeds.

This test should remain skipped (via vm.skip) until #121 is fixed, but the test skeleton should exist so the fix author knows exactly what to verify.

Refs #38, Refs #121

[obchain]

Deferred. This branch's CharonLiquidator has no vBNB native unwrap path — the callback always treats collateralToken as an ERC-20 and swaps it through the PCS V3 router. The native-BNB / WBNB wrap logic arrives with the feat/12-charon-liquidator-full rebase (commit 19bce9a). Once feat/12 rebases onto feat/13, the vBNB native-collateral path test will be added to contracts/test/CharonLiquidatorFork.t.sol as part of PR #53 (feat/25-foundry-fork-tests), per issue #268. Tracked for post-rebase follow-up.