# Vault

The **Vault** is a Program-Derived Address (PDA) owned by Klink's Anchor program. One per human. It holds USDC via its associated token account (ATA), and it's the on-chain anchor for every per-wallet policy decision.

## Account layout

```rust
struct Vault {
    owner: Pubkey,                   // human's Phantom pubkey — master authority
    max_deployed_fraction_bp: u16,   // basis points; e.g. 8000 = 80%
    deployed_amount: u64,            // current yield deposit (USDC base units)
    bump: u8,
}
// Approximate size: 80 bytes  →  rent ~$0.20 at $200/SOL
```

## Seeds

```
seeds = ["vault", owner.key()]
```

The PDA is fully derivable from the owner's Phantom pubkey. There is no global registry, given any owner pubkey, anyone can compute the vault address.

## Fields

| Field                      | Type     | Meaning                                                                                                                                                                             |
| -------------------------- | -------- | ----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- |
| `owner`                    | `Pubkey` | Human's Phantom pubkey. Master authority, only this key can run owner-only instructions (`set_max_deployed_fraction`, `add_session`, `revoke_session`, `update_session_allowlist`). |
| `max_deployed_fraction_bp` | `u16`    | Basis points (0–10000). Hard cap on the fraction of total USDC that may sit in yield at any moment. Adjustable by owner via `set_max_deployed_fraction`.                            |
| `deployed_amount`          | `u64`    | Current USDC deposited in the yield protocol, in base units (1 USDC = 1\_000\_000). Updated atomically on every `kamino_deposit` / `kamino_withdraw`.                               |
| `bump`                     | `u8`     | PDA bump byte.                                                                                                                                                                      |

## USDC custody

The vault doesn't hold USDC directly. Like every SPL-token holder, it has an Associated Token Account at a derived address:

```
spl_associated_token_account.get_associated_token_address(
    wallet_address: vault_pda,
    token_mint_address: USDC_MINT,
)
```

USDC sent to that ATA is owned (in the SPL-token sense) by the vault PDA, which means only the program can move it, and the program only moves it when called via one of its signed instructions.

## Account-creation cost

| Account        | One-time rent | Refundable on close |
| -------------- | ------------- | ------------------- |
| Vault PDA      | \~$0.20       | Yes                 |
| Vault USDC ATA | \~$0.50       | Yes                 |

Both costs are sponsorable by the backend at creation time.

## Lifecycle

```mermaid
stateDiagram-v2
    [*] --> Initialized: init_vault(max_deployed_fraction_bp)
    Initialized --> Initialized: set_max_deployed_fraction(bp)
    Initialized --> Initialized: kamino_deposit / kamino_withdraw\n(adjusts deployed_amount)
    Initialized --> Initialized: transfer_usdc\n(via session signer)
```

The vault has no terminal state, there is no "close vault" instruction. The owner key is the master authority for the lifetime of the vault.

## What the vault does NOT contain

* **No session list.** Sessions live in their own per-session PDA accounts ([Sessions](/klink-docs/core-concepts/sessions.md)).
* **No URL allowlist.** That's off-chain ([Policies](/klink-docs/core-concepts/policies.md) → off-chain rich rules).
* **No history.** That's the Solana transaction log ([Audit Trail](/klink-docs/core-concepts/audit-trail.md)).

## Read next

* [Sessions](/klink-docs/core-concepts/sessions.md): the per-agent account that delegates authority
* [Budgets](/klink-docs/core-concepts/budgets.md): how `max_deployed_fraction_bp` interacts with yield


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