[PR #31] Missing chain ID check after WebSocket handshake — wrong-chain connection undetected

[obchain]

PR: #31 (feat/06-chainprovider-ws)
File: crates/charon-scanner/src/provider.rs
Lines: 36-43

Problem: ChainProvider::connect establishes WebSocket and returns Ok(Self) without calling eth_chainId to verify endpoint is BSC (chain ID 56). Misconfigured URL pointing at Ethereum mainnet (chain ID 1) silently succeeds.

Impact: Liquidation transactions broadcast to wrong chain waste gas and fail silently. All subsequent scanner state (block numbers, contract addresses) invalid for BSC. PRD requires BSC-only operation.

Fix: Add expected_chain_id: u64 to ChainConfig (default 56). After on_ws succeeds:

let actual = provider.get_chain_id().await
    .context("chain '{name}': eth_chainId probe failed")?;
anyhow::ensure!(
    actual == config.expected_chain_id,
    "chain '{name}': expected chain ID {}, got {actual}",
    config.expected_chain_id
);

[obchain]

Fixed on feat/06-chainprovider-ws in cc0519c.