[flashloan] AaveFlashLoan::connect() does not assert chain_id == 56

[obchain]

Refs #39

File: crates/charon-flashloan/src/aave.rs — AaveFlashLoan::connect()

Problem

The adapter reads chain_id from the provider and caches it but does not validate it is 56 (BSC mainnet). CLAUDE.md scope: Venus on BNB Chain only. A misconfigured RPC URL pointing at another chain will silently connect and produce flash-loan calldata targeting the wrong Aave V3 Pool address. Because Aave V3 uses different Pool addresses per chain (BSC: 0x6807dc923806fe8fd134338eabca509979a7e0cb; Ethereum: 0x87870Bca3F3fD6335C3F4ce8392D69350B4fA4E2), cross-chain confusion is silent at connect time and only surfaces as a revert at execution time.

Fix

anyhow::ensure!(
    chain_id == 56,
    "AaveFlashLoan: expected BSC mainnet (chain 56), connected to chain {chain_id}"
);

[obchain]

Resolved in b9092e1 on feat/14-flashloan-router. AaveFlashLoan::connect calls provider.get_chain_id() and anyhow::ensure!s the result equals BSC_CHAIN_ID (56) before any pool calls. Misconfigured RPC endpoints now fail with a clear "Aave V3 adapter is BSC-only for v0.1: expected chain_id 56, got N" error instead of silently returning bogus liquidity.