Explain L1 lockbox

Author: qbzzt

pages/stack/interop/superchain-weth.mdx

@@ -12,7 +12,13 @@ import { InteropCallout } from '@/components/WipCallout'
 
 # Interoperable ETH
 
-InteroperableETH is implemented using the [`SuperchainWETH`](https://github.com/ethereum-optimism/optimism/blob/develop/packages/contracts-bedrock/src/L2/SuperchainWETH.sol) contract, along with [`ETHLiquidity`](https://github.com/ethereum-optimism/optimism/blob/develop/packages/contracts-bedrock/src/L2/ETHLiquidity.sol), and [`L2ToL2CrossDomainMessenger`](https://github.com/ethereum-optimism/optimism/blob/develop/packages/contracts-bedrock/src/L2/L2ToL2CrossDomainMessenger.sol) to enable ETH interoperability within the Superchain.
+InteroperableETH is implemented using three contacts:
+
+- [`SuperchainWETH`](https://github.com/ethereum-optimism/optimism/blob/develop/contracts-bedrock/src/L2/SuperchainWETH.sol) is the bridge that lets you move ETH from one Superchain blockchain to another.
+- [`ETHLiquidity`](https://github.com/ethereum-optimism/optimism/blob/develop/packages/contracts-bedrock/src/L2/ETHLiquidity.sol) holds a practically infinite amount of ETH (it starts with 2<sup>248</sup> WEI).
+  It is used by `SuperchainWETH` as a liquidity repository to be able to provide ETH on the destination chain.
+- [`L2ToL2CrossDomainMessenger`](https://github.com/ethereum-optimism/optimism/blob/develop/packages/contracts-bedrock/src/L2/L2ToL2CrossDomainMessenger.sol) is used to [pass messages between different chains](./message-passing).
+
 InteroperableETH works by depositing ETH on the source chain's `ETHLiquidity` and withdrawing an equivalent amount on the destination chain.
 This approach addresses issues such as liquidity fragmentation and poor user experiences caused by asset wrapping or reliance on liquidity pools.
 
@@ -91,6 +97,43 @@ sequenceDiagram
 7.  `SuperchainWETH` uses [`SafeSend`](https://github.com/ethereum-optimism/optimism/blob/develop/packages/contracts-bedrock/src/universal/SafeSend.sol) to send the ETH.
     This means that even if the destination is a smart contract, its custom logic does not get called, [in contrast to normal ETH transfers](https://docs.base.org/base-learn/docs/address-and-payable/#receiving-ether-with-payable-addresses).
 
+
+## L1 Treasury
+
+All the ETH in circulation on the Superchain (all the ETH except for what is held by `ETHLiquidity`) needs to be backed by real ETH held on L1.
+This is done by the . 
+
+Here is an example of how this works.
+
+| Step | User on L1 | Lockbox | User on chain A | ETHLiquidity on chain A | User on chain B | ETHLiquidity on chain B |
+| -: | -: | -: | -:| -: | -: | -: |
+| 1 | 7 | 200 | 0 | 100000 | 0 | 100000
+| 2 | 4 | 203 | 3 | 100000 | 0 | 100000
+| 3 | 4 | 203 | 2 | 100001 | 0 | 100000
+| 4 | 4 | 203 | 2 | 100001 | 1 |  99999
+| 5 | 4 | 203 | 2 | 100001 | 0 |  99999
+| 6 | 5 | 202 | 2 | 100001 | 0 |  99999
+
+1. The initial state. The user has 7 ETH on L1, and nothing on chains A and B.
+
+2. The user bridges 3 ETH to chain A.
+   The user sends 3 ETH on L1 to the bridge, which is locked in the lockbox.
+   The bridge on chain A then mints 3 ETH for the user.
+
+3. The user sent the initiating message to `SuperchainWETH` on chain A, along with 1 ETH to bridge to chain B. 
+   This 1 ETH is sent to `ETHLiquidity` on chain A.
+
+4. Somebody (the user, a relayer action on behalf of the user, etc.) sent the corresponding executing message to chain B.
+   `SuperchainWETH` transfers 1 ETH from `ETHLiquidity` on chain B to the user.
+
+5. The user decides to withdraw 1 ETH from chain B back into L1.
+   Normally a user would do this through a third party bridge, which is faster and usually cheaper, but for illustration purposes this user uses the standard OP bridge.
+   The user starts with an initiating message on chain B, which burns 1 ETH and sends a message to L1.
+
+6. After the week long [challenge period](/connect/resources/glossary#challenge-period), the user finalizes the withdrawal on L1. 
+   The lock box releases 1 ETH, which is then sent to the user.
+
+
 ## Next steps
 
 *   Explore [the `SuperchainWETH` specs](https://specs.optimism.io/interop/superchain-weth.html) for in-depth implementation details.