[Task]: Add a withdraw_all(user, asset) convenience function

[grantfox-oss]

To fully exit an asset today, a user must first read their available balance (get_available) off-chain and then submit a withdraw for that exact amount. This is a race: if a task completes between the read and the withdraw, the available balance changes and the user either leaves dust behind or over-requests and reverts with InsufficientAvailable.

Add a withdraw_all that computes the withdrawable amount on-chain and transfers exactly the unlocked portion in a single call:

pub fn withdraw_all(env: Env, user: Address, asset: Address) -> Result<i128, VaultError> {
    user.require_auth();
    let asset_key = DataKey::UserAsset(user.clone(), asset.clone());
    let account: UserAssetAccount = env.storage().persistent()
        .get(&asset_key).ok_or(VaultError::InsufficientBalance)?;
    let available = account.balance - account.locked;
    if available <= 0 {
        return Err(VaultError::InsufficientAvailable);
    }
    Self::withdraw(env, user, asset, available)?; // reuse existing logic + event
    Ok(available)
}

Reusing withdraw means the existing per-asset locked guard, the WithdrawEvent, TTL bumps, and logging all apply unchanged — this function is purely a safe "max" wrapper. It returns the amount withdrawn so the caller can display it.

Acceptance criteria

• withdraw_all(env, user, asset) -> Result<i128, VaultError> withdraws exactly balance - locked for that asset
• Returns the amount withdrawn
• Errors with InsufficientAvailable when nothing is withdrawable (all locked or zero balance)
• Leaves locked funds untouched; a subsequent task completion still refunds correctly
• Emits WithdrawEvent (via reuse of withdraw)
• Tests cover: full withdrawal, withdrawal with some funds locked, and the nothing-available case
• cargo test and cargo clippy --all-targets -- -D warnings pass

Relevant files

• contracts/agent-vault/src/lib.rs (new function reusing withdraw)
• contracts/agent-vault/src/tests.rs

Notes for contributors

If you'd like to work on this, comment below so we can assign it to you.
Questions welcome — see CONTRIBUTING.md for setup
and workflow.

[mxrtins04]

Hi maintainer, can i be assigned this issue pleasee?

[aristotle224]

I can deliver an excellent work on this, please assign me

[grantfox-oss]

🦊 GrantFox — @mxrtins04 has been assigned to this issue as part of the Official Campaign | FWC26 campaign!

Next steps:

1. Open a Pull Request referencing this issue (e.g., Closes #67)
2. Your PR will be reviewed by the clevercon-protocol maintainers

Good luck! Track your progress on GrantFox.