# Vault

The vault is a standard ERC-4626 tokenized vault with **USDC as the underlying asset** and **USDREFI as the share token**. Because yield is distributed as a side-stream via Merkl (rather than accruing into the share price), the exchange rate is always **1:1**.

## Deposit Functions (Active)

| Function                         | Behavior                                                                    |
| -------------------------------- | --------------------------------------------------------------------------- |
| `deposit(assets, receiver)`      | Accepts USDC, mints USDREFI 1:1. Checks tier and caps. Reverts if tier = 0. |
| `mint(shares, receiver)`         | Same logic, denominated in shares.                                          |
| `maxDeposit(receiver)`           | Returns `min(globalRemaining, tierCapRemaining)`. Returns 0 if tier = 0.    |
| `maxMint(receiver)`              | Equivalent to maxDeposit at 1:1 rate.                                       |
| `previewDeposit` / `previewMint` | Identity function (1:1).                                                    |

## Withdrawal Functions (Disabled)

| Function                    | Behavior                                        |
| --------------------------- | ----------------------------------------------- |
| `maxWithdraw` / `maxRedeem` | Return 0 — signals withdrawals unavailable.     |
| `withdraw` / `redeem`       | Revert with message directing users to Uniswap. |

{% hint style="info" %}
The Foundation Safe can call `setWithdrawalsEnabled(true)` to re-enable withdrawals in an emergency. This toggle can be reversed once the Uniswap pool is restored.
{% endhint %}

## Cap System

| Parameter           | Initial Value | Governance                                   |
| ------------------- | ------------- | -------------------------------------------- |
| Global vault cap    | $25,000 USDC  | `setGlobalCap(uint256)` via Foundation Safe  |
| Tier 1 per-user cap | $500 USDC     | `setTierCap(1, uint256)` via Foundation Safe |
| Tier 2 per-user cap | $5,000 USDC   | `setTierCap(2, uint256)` via Foundation Safe |
| Tier 3 per-user cap | $15,000 USDC  | `setTierCap(3, uint256)` via Foundation Safe |

The `maxDeposit` function enforces both the global cap and the per-user tier cap, returning the lower of the two remaining amounts.

## ERC-4626 Compliance

The vault is fully ERC-4626 compliant despite disabled withdrawals. The standard explicitly allows `maxWithdraw()` and `maxRedeem()` to return 0, signaling to integrators that withdrawals are unavailable. Portfolio trackers (DeBank, Zapper) will correctly display the position, and all deposit-side view functions work normally.

## Implementation Notes

* Built on OpenZeppelin's ERC4626 base with overrides for `maxDeposit`, `maxMint`, `maxWithdraw`, `maxRedeem`, `deposit` (cap checks), and `totalAssets`
* `totalAssets()` uses an internal counter — not `token.balanceOf(address(this))` — to avoid counting dust or direct transfers
* First-depositor inflation attack is not a risk at fixed 1:1 pricing
* `maxDeposit` never overestimates — returns 0 on any overflow rather than reverting