[Bug] Zero slippage floor on the on-chain DeFindex adapter's deposit/withdraw

[collinsezedike]

Description

DefindexAdapter::deposit/withdraw pass 0 as the minimum acceptable amount on both legs of their interaction with the underlying DeFindex vault, accepting any execution price the DeFindex vault happens to offer.

Closed issues #117 and #432 fixed the identical bug class, but only in packages/stellar-sdk-helpers/src/defindex.ts, the off-chain transaction builder. Neither touches the on-chain adapter that MeridianVault::deposit/withdraw actually invoke and which carries pooled depositor funds directly. The on-chain path still hardcodes a zero floor on both legs.

Steps to Reproduce

1. Have a MeridianVault routed through DefindexAdapter.
2. Call deposit() or withdraw() while the underlying DeFindex vault's execution price is unfavorable (e.g. during unusual market conditions or a manipulated quote).
3. The adapter accepts whatever price results, since it passes 0 as the minimum on-chain.

Expected Behavior

The on-chain adapter should reject execution below a defined tolerance, the same protection already applied off-chain in the transaction builder.

Actual Behavior

Both deposit and withdraw pass a literal 0 minimum to the underlying DeFindex vault calls.

Environment

Field	Value
Network	testnet / mainnet
Wallet	N/A (contract-level)
Protocol affected	DeFindex
Browser (if frontend)	N/A
Node.js version	N/A
pnpm version	N/A

Transaction Details (if on-chain)

• Transaction hash: N/A — identified by static review
• Ledger: N/A
• Soroban RPC endpoint used: N/A

Logs / Screenshots

defindex-adapter/src/lib.rs:94, 111-112
// both legs pass 0 as the minimum acceptable amount

Possible Cause / Fix

Apply a real basis-point tolerance (0.5% suggested) on both legs, matching the constraint #117 already established there: a floor set to the exact expected amount causes spurious reverts on ordinary rounding, so the tolerance needs headroom, not an exact match.

Scope

Field	Value
Area	Contracts
Protocol affected	DeFindex
Network	testnet, mainnet
Breaking change?	No — tightens accepted execution range only

[habnark]

@habnark has applied to work on this issue as part of the Stellar Wave Program's 8th wave.

Hi maintainer can i work on this issue

ℹ️ Repo Maintainers: To accept this application, review their application or assign @habnark to this issue.

[drips-wave]

Congratulations, @habnark! 🎉 Your application was accepted by the repo's maintainers, and the issue is due on August 31, 2026.

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[grantfox-oss]

🎉 This issue has been marked as completed on GrantFox!

@habnark's PR #622 was approved and merged by @collinsezedike.

🏆 @habnark: You earned 35 FoxPoints for this contribution! Your current tier: Explorer (774 total points). Track your full progress on GrantFox.

👏 Great work, @habnark! Keep contributing to drydocs.