core: implement share price calculation in liquidity pool

[EmeditWeb]

Problem

The liquidity pool has total_shares and total_deposits
but no mechanism to calculate the actual share price.
This breaks the yield mechanism entirely.

What To Build

1. Add share price calculation
2. Fix deposit() to issue shares at current price
3. Fix withdraw() to calculate USDC from shares
4. Add accumulate_interest()

Files To Touch

• contracts/liquidity-pool-contract/src/lib.rs
• contracts/liquidity-pool-contract/src/types.rs
• contracts/liquidity-pool-contract/src/storage.rs
• contracts/liquidity-pool-contract/src/tests.rs

Acceptance Criteria

• Share price calculated correctly
• New deposits issued at current share price
• Withdrawals return correct USDC amount
• Interest increases share price for all holders
• All arithmetic uses checked operations

Mandatory Checks Before PR

• cargo build passes
• All tests pass
• No integer overflow possible
• PR references this issue

[Vicsygold]

BOSS PLS I NEED THIS PROJECT

[divicbold47]

Hello maintainer, pls assign me this task

[KingFRANKHOOD]

Hi Team, I would love to take on this issue. Fixing the share price calculation and integrating interest accumulation is vital for restoring the pool's core yield mechanics. I will ensure the entire implementation is mathematically sound, defensive, and completely free of overflow risks.

To implement this, I will first introduce the share price calculation formula in lib.rs, which derives the price as the ratio of total_deposits to total_shares. To protect against division-by-zero errors when the pool is completely empty, I will implement a safe fallback that initializes the starting share price at a 1:1 ratio.

Once the pricing mechanism is established, I will update both deposit() and withdraw() to utilize this live rate. The deposit() function will compute the exact number of shares to mint based on the current price, while withdraw() will translate burning shares back into the precise amount of underlying USDC owed to the user. Every single mathematical calculation across these functions will be refactored to use strictly checked arithmetic operations to eliminate any possibility of integer overflow or underflow under high volume.

Furthermore, I will implement the accumulate_interest() function to cleanly increase the total_deposits pool balance over time, which will naturally drive up the share price and distribute yield evenly to all current token holders. Finally, I will expand the test suite in src/tests.rs with comprehensive edge cases to verify that interest accrual reflects correctly in the share value and that deposits and withdrawals scale perfectly across fluctuating prices.

[grantfox-oss]

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

Next steps:

1. Open a Pull Request referencing this issue (e.g., Closes #16)
2. Your PR will be reviewed by the StepFi-app maintainers

Good luck! Track your progress on GrantFox.

[grantfox-oss]

🎉 This issue has been marked as completed on GrantFox as part of the Official Campaign campaign!

@KingFRANKHOOD's PR #39 was approved and merged by @EmeditWeb.

🏆 @KingFRANKHOOD: You earned 35 FoxPoints for this contribution! Your current tier: Explorer (83 total points). Track your full progress on GrantFox.

👏 Great work, @KingFRANKHOOD! Keep contributing to StepFi-app.