Bounds check Solver::swap return in trade verifier

[squadgazzz]

Description

TradeVerifier::SettleOutput::from_swap indexes the queriedBalances array returned from the on-chain Solver helper without checking its length. The function expects 2 * tokens.len() + 2 entries laid out as [...tokens_before, user_before, user_after, ...tokens_after]. When the helper returns fewer entries the indexing panics with index out of bounds: the len is 4 but the index is 4, killing the orderbook tokio worker.

The panic was observed on barn while submitting a wrapper-bearing order: POST /api/v1/orders re-runs the quoter via get_quote_and_check_fee, the verified estimator drives TradeVerifier::verify_inner and crashes inside from_swap. The container restart loop surfaces as 502s and looks like OOM in metrics.

A separate investigation is needed for why the helper returns a short response for wrapper-bearing orders (Bug B). This PR addresses only the panic so the verifier fails soft.

Changes

• Validate queriedBalances.len() against the expected 2 * tokens.len() + 2 at the top of SettleOutput::from_swap and return a descriptive anyhow error if the shape is unexpected. Callers up the stack already surface this as Error::SimulationFailed (unverified quote) instead of panicking.

How to test

New unit tests cover both the error path (short response) and the happy path.

[gemini-code-assist]

Code Review

This pull request introduces a length validation check for queriedBalances in SettleOutput::from_swap to prevent out-of-bounds panics when the solver returns an unexpected number of balances. Regression and success unit tests have been added to ensure correct error handling and normal operation. No critical issues found; I have no feedback to provide.