Euler Evc

---
name: Ethereum Vault Connector (EVC)
description: This skill should be used when the user asks about "EVC", "Ethereum Vault Connector", "sub-accounts", "collateral", "controller", "batch", "permit", "status checks", or needs to understand Euler's foundational infrastructure.
version: 0.1.0
---

# Ethereum Vault Connector (EVC)

The EVC is the foundational infrastructure layer that enables cross-vault coordination in Euler's lending ecosystem. It mediates all vault interactions, manages sub-accounts, and enforces solvency through deferred status checks.

## Overview

```
┌──────────────────────────────────────────────────────────────┐
│               ETHEREUM VAULT CONNECTOR                       │
├──────────────────────────────────────────────────────────────┤
│                                                              │
│  User (Owner)                                                │
│  └── 256 Sub-Accounts (0-255)                                │
│       │                                                      │
│       ├── Sub-Account 0: Main position                       │
│       │   ├── Collateral: [Vault A, Vault B]                 │
│       │   └── Controller: Vault C (lending)                  │
│       │                                                      │
│       ├── Sub-Account 1: Isolated position                   │
│       │   ├── Collateral: [Vault D]                          │
│       │   └── Controller: Vault E                            │
│       │                                                      │
│       └── Sub-Account N: ...                                 │
│                                                              │
│  EVC Functions:                                              │
│  ├── call() - Route calls with deferred checks               │
│  ├── batch() - Execute multiple operations atomically        │
│  ├── controlCollateral() - Liquidation collateral seizure    │
│  ├── permit() - EIP-712 gasless authorization                │
│  ├── enableCollateral/disableCollateral                      │
│  └── enableController/disableController                      │
│                                                              │
└──────────────────────────────────────────────────────────────┘
```

## Sub-Account Model

Each Ethereum address gets 256 sub-accounts via address prefix encoding:

```solidity
// Sub-account address = owner address XOR account ID
// Account ID is in the last byte (0-255)

function getAddressPrefix(address account) internal pure returns (bytes19) {
    return bytes19(uint152(uint160(account) >> 8));
}

function getSubAccount(address owner, uint8 subAccountId) internal pure returns (address) {
    return address(uint160(owner) ^ uint160(subAccountId));
}

// Examples:
// Owner: 0x1234...5678
// Sub-account 0: 0x1234...5678 (same as owner)
// Sub-account 1: 0x1234...5679
// Sub-account 255: 0x1234...5687
```

Benefits:
- Isolated positions without new approvals
- Each sub-account has independent collateral/controller
- Cross-sub-account operations within same owner

## Collateral and Controller

```solidity
// Storage per account
mapping(address account => SetStorage) internal accountCollaterals;  // Max 10
mapping(address account => SetStorage) internal accountControllers;  // Max 10 (1 at check time)

// Enable collateral vault for an account
function enableCollateral(address account, address vault) external payable {
    // Authenticate caller
    // Add vault to account's collateral set
    // Emit CollateralStatus(account, vault, true)
}

// Enable controller (lending vault) for an account
function enableController(address account, address vault) external payable {
    // Only the account itself or authorized operator
    // Add vault to account's controller set
    // Emit ControllerStatus(account, vault, true)
}

// Get enabled collaterals/controllers
function getCollaterals(address account) external view returns (address[] memory);
function getControllers(address account) external view returns (address[] memory);
function isCollateralEnabled(address account, address vault) external view returns (bool);
function isControllerEnabled(address account, address vault) external view returns (bool);
```

**Key Distinction:**
- **Collateral Vaults**: Where user deposits assets as collateral
- **Controller Vaults**: Lending vaults that can control collateral (for liquidations)

## Deferred Status Checks

The EVC defers solvency checks until the end of a batch, allowing temporary insolvency during multi-step operations:

```solidity
// Execution context tracking
struct ExecutionContext {
    uint256 batchDepth;           // Nesting level of batches
    bool checksDeferred;          // Whether checks are currently deferred
    bool controlCollateralInProgress;
    address onBehalfOfAccount;    // Current authenticated account
    // ... status check sets
}

// Require a status check at batch end
function requireAccountStatusCheck(address account) external payable {
    // Schedule check - will be called at batch end
    executionContext.accountStatusChecks.insert(account);
}

function requireVaultStatusCheck(address vault) external payable {
    executionContext.vaultStatusChecks.insert(vault);
}

// Called on each scheduled account at batch end
interface IVault {
    function checkAccountStatus(
        address account,
        address[] calldata collaterals
    ) external view returns (bytes4 magicValue);
    // Returns 0xe90a5c72 (selector) if healthy
    // Reverts if unhealthy
}
```

## Call and Batch Operations

### Call (Single Operation)

```solidity
/// @notice Execute a call through EVC with deferred checks
function call(
    address targetContract,
    address onBehalfOfAccount,
    uint256 value,
    bytes calldata data
) external payable returns (bytes memory) {
    // Authenticate: caller must be owner or operator of onBehalfOfAccount
    // Set execution context
    // Forward call to targetContract
    // At end: run deferred status checks
}
```

### Batch (Multiple Operations)

```solidity
struct BatchItem {
    address targetContract;
    address onBehalfOfAccount;
    uint256 value;
    bytes data;
}

/// @notice Execute multiple operations atomically
function batch(BatchItem[] calldata items) external payable {
    // All operations share deferred check context
    // Status checks run once at the very end
    // Entire batch reverts if any check fails
}

// Example: Add collateral and borrow in one atomic batch
BatchItem[] memory items = new BatchItem[](2);
items[0] = BatchItem({
    targetContract: collateralVault,
    onBehalfOfAccount: myAccount,
    value: 0,
    data: abi.encodeCall(IVault.deposit, (amount, myAccount))
});
items[1] = BatchItem({
    targetContract: lendingVault,
    onBehalfOfAccount: myAccount,
    value: 0,
    data: abi.encodeCall(IVault.borrow, (borrowAmount, myAccount))
});
evc.batch(items);
// Status check happens here - must be solvent after both operations
```

## Control Collateral (Liquidation)

```solidity
/// @notice Controller vault seizes collateral during liquidation
function controlCollateral(
    address collateralVault,
    address onBehalfOfAccount,
    uint256 value,
    bytes calldata data
) external payable returns (bytes memory) {
    // Only callable by enabled controller of the account
    // Temporarily grants controller power over collateral vault
    // Used for transferring collateral to liquidator
}
```

## Authentication and Operators

```solidity
/// @notice Check if an operator is authorized for an account
function isAccountOperatorAuthorized(
    address account,
    address operator
) external view returns (bool);

/// @notice Authorize an operator for your accounts
function setAccountOperator(
    address account,
    address operator,
    bool authorized
) external payable;

// Internal authentication
function authenticateCaller(address account) internal view returns (bool) {
    // True if:
    // 1. Caller is the account owner (same prefix)
    // 2. Caller is an authorized operator
    // 3. EVC is calling on behalf of authenticated context
}
```

## Permit (Gasless Operations)

```solidity
/// @notice Execute operations via EIP-712 signature
function permit(
    address signer,
    address sender,          // Who can submit the permit
    uint256 nonceNamespace,  // Nonce namespace for replay protection
    uint256 nonce,
    uint256 deadline,
    uint256 value,
    bytes calldata data,     // Encoded batch or single call
    bytes calldata signature // ECDSA or ERC-1271
) external payable;

// Nonce management
function getNonce(
    bytes19 addressPrefix,
    uint256 nonceNamespace
) external view returns (uint256);

// Invalidate nonces (cancel pending permits)
function setNonce(
    bytes19 addressPrefix,
    uint256 nonceNamespace,
    uint256 nonce
) external payable;
```

## Address Prefix Security

Owner-level controls that apply to all sub-accounts:

```solidity
/// @notice Lock down all accounts under this prefix
function setLockdownMode(
    bytes19 addressPrefix,
    bool enabled
) external payable;
// When locked: no new collateral/controller can be enabled

/// @notice Disable permit for this prefix
function setPermitDisabledMode(
    bytes19 addressPrefix,
    bool enabled
) external payable;
// Prevents gasless operations

// Check status
function isLockdownMode(bytes19 addressPrefix) external view returns (bool);
function isPermitDisabledMode(bytes19 addressPrefix) external view returns (bool);
```

## Execution Context

```solidity
// Get current execution context
function getCurrentOnBehalfOfAccount(
    address controllerToCheck
) external view returns (address, bool);
// Returns (account, isControllerEnabled)

function areChecksDeferred() external view returns (bool);

function isControlCollateralInProgress() external view returns (bool);

// Useful for vaults to understand current context
function getRawExecutionContext() external view returns (uint256);
```

## Events

```solidity
event CollateralStatus(address indexed account, address indexed collateral, bool enabled);
event ControllerStatus(address indexed account, address indexed controller, bool enabled);
event AccountOperatorAuthorized(address indexed account, address indexed operator, uint256 authMask);
event NonceUsed(bytes19 indexed addressPrefix, uint256 indexed nonceNamespace, uint256 nonce);
event LockdownModeSet(bytes19 indexed addressPrefix, bool enabled);
event PermitDisabledModeSet(bytes19 indexed addressPrefix, bool enabled);
```

## Status Check Flow

```
┌──────────────────────────────────────────────────────────────┐
│                STATUS CHECK EXECUTION                        │
├──────────────────────────────────────────────────────────────┤
│                                                              │
│  1. User calls evc.batch([deposit, borrow])                  │
│     └── checksDeferred = true                                │
│                                                              │
│  2. deposit() executes                                       │
│     └── vault.requireAccountStatusCheck(account)             │
│         └── Adds account to check set (deferred)             │
│                                                              │
│  3. borrow() executes                                        │
│     └── vault.requireAccountStatusCheck(account)             │
│         └── Already in set (no-op)                           │
│                                                              │
│  4. Batch ends, checks execute:                              │
│     └── For each account in check set:                       │
│         └── controller.checkAccountStatus(account, collats)  │
│             └── Returns magic value if healthy               │
│             └── Reverts if unhealthy                         │
│                                                              │
│  5. If any check fails → entire batch reverts                │
│                                                              │
└──────────────────────────────────────────────────────────────┘
```

## Reference Files

- `ethereum-vault-connector/src/EthereumVaultConnector.sol` - Main EVC contract
- `ethereum-vault-connector/src/Set.sol` - Set data structure for collateral/controllers
- `ethereum-vault-connector/src/ExecutionContext.sol` - Execution context management
- `ethereum-vault-connector/src/interfaces/IEthereumVaultConnector.sol` - Full interface