Verify close/liquidation event bindings against the live deployment (v0.2.1 drift)

[Praz314159]

Background

While adding realized swap deltas to trade results (PR feat/realized-swap-results), we discovered the deployed Arbitrum Sepolia contract is not the v0.2.1 source tag — it was built from a later commit that unified close + liquidation events.

Concretely, the deployed TakerClosed is:

TakerClosed(uint256 posId, SwapResult sr, int256 funding, uint256 utilFees, uint256 liqFee, bool isLiquidation)

(two extra trailing fields vs the v0.2.1 source / old binding). Verified against the live log topic0 0xc6d1565765c65beb63cd0a76e37c058e0908e6e24a609d0dc1a724106ae0576e. That binding is now fixed, with a SIGNATURE_HASH regression assertion in abi_lock.

The risk

The same drift likely affects the other close/liquidation events, which were not emitted in the open/adjust/close fork test and so remain unverified against the chain:

• MakerClosed
• TakerLiquidated
• MakerLiquidated
• possibly MakerAdjusted / MakerConverted

If any binding's topic0 doesn't match the deployed event, decode_log silently returns None and the event is dropped. Legion's market_data.rs depends on these for external-close/liquidation eviction, so a mismatch means it never notices a position was closed/liquidated out from under it.

Why the easy routes don't work

• The contracts are not verified on the Arbitrum Sepolia explorer (blockscout getabi → "not verified"), so no ABI to pull.
• The abi_lock test only checks each binding against itself, not against the chain — it won't catch deployment drift.

Proposed work

1. Add a fork test that emits each event (open→close a maker; stage a liquidation if feasible) and capture the real topic0s.
2. For each, compute cast keccak of the candidate signature (with SwapResult expanded to its 7-field tuple) and compare; fix any mismatched sol! binding in contracts.rs.
3. Add SIGNATURE_HASH assertions to abi_lock for each, so future drift is caught.

See memory note / PR feat/realized-swap-results for the verification method.