[Contracts] LendingPool MaxPoolSize cap and DepositorCount drift from real state under the share model

[grantfox-oss]

Telegram (ask questions / claim the issue here first): https://t.me/+DOylgFv1jyJlNzM0

Why this matters

In lending_pool/src/lib.rs, the MaxPoolSize cap in deposit is enforced against TotalDeposits, but redeem_shares decrements TotalDeposits by assets_to_return (principal + yield) using saturating_sub, so after withdrawals that include yield, TotalDeposits can saturate to 0 or understate principal, corrupting the cap. DepositorCount is incremented only when existing_shares == 0 but a partial withdrawal that leaves remaining > 0 keeps the depositor, while a full withdrawal decrements via saturating_sub(1); combined re-deposits/withdrawals can desync the count.

Acceptance criteria

• Make TotalDeposits track net principal consistently (do not subtract accrued yield) so the MaxPoolSize cap stays meaningful
• Ensure DepositorCount cannot drift across deposit/partial-withdraw/full-withdraw/re-deposit sequences
• Add multi-operation tests asserting cap enforcement and depositor_count remain correct after yield accrual and partial withdrawals
• Document the intended meaning of TotalDeposits vs pool_token_balance

Files to touch

• lending_pool/src/lib.rs

Out of scope

• Per-depositor cost-basis tracking
• Cap policy redesign

[Lansa-18]

Hi, I'd like to work on this.
I'll fix TotalDeposits in lending_pool/src/lib.rs so it tracks net principal only and never subtracts accrued yield during redeem_shares, keeping the MaxPoolSize cap meaningful. I'll also tighten DepositorCount so it stays in sync across deposit, partial withdrawal, full withdrawal, and re-deposit sequences, including edge cases where the saturating operations can currently let the count drift. I'll add multi-operation tests asserting cap enforcement and depositor count correctness after yield accrual and partial withdrawals, and add a short doc comment clarifying the intended difference between TotalDeposits and pool_token_balance.

[grantfox-oss]

🦊 GrantFox — @Lansa-18 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 #9)
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