Implement Share Transfer Lock-Up Period After Deposit

[Jayy4rl]

Description

RWA securities typically have lock-up periods where shares cannot be transferred or redeemed for a specified duration after purchase. The current contract allows immediate transfer of shares after deposit — a user can deposit, receive shares, and transfer them in the same ledger. This undermines:

1. Regulatory compliance — many jurisdictions require holding periods for securities
2. Anti-speculation — prevents deposit-and-flip arbitrage
3. Yield fairness — prevents gaming the epoch snapshot system by depositing just before a yield distribution and transferring immediately after

Requirements

• Add a lock_up_period: u64 field to InitParams (seconds after deposit during which shares are non-transferable)
• Store DataKey::DepositTimestamp(Address) → u64 — the timestamp of the user's last deposit
• In transfer, transfer_from, withdraw, redeem, and request_early_redemption: check that e.ledger().timestamp() >= deposit_timestamp + lock_up_period
• redeem_at_maturity should bypass the lock-up (the vault has matured, users must be able to exit)
• Add error variant: Error::SharesLocked
• Add a view function: lock_up_remaining(user: Address) -> u64
• Allow admin to update lock_up_period for future deposits (existing deposits keep their original lock-up)

Key Files

• types.rs — InitParams new field
• lib.rs — transfer, transfer_from, withdraw, redeem, request_early_redemption
• storage.rs — new LockUpPeriod, DepositTimestamp(Address) keys
• errors.rs — new SharesLocked variant

Definition of Done

• Shares cannot be transferred or redeemed during lock-up
• Lock-up is configurable at construction and updatable by admin
• redeem_at_maturity bypasses lock-up
• View function shows remaining lock-up time
• Tests cover lock-up enforcement and bypass scenarios

[Nanle-code]

@Nanle-code has applied to work on this issue as part of the Stellar Wave Program's 3rd wave.

let me work on this issue

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