Add slippage protection parameter to buy and sell functions

[Chucks1093]

Summary

Extend buy and sell contract functions with an optional max_slippage_bps parameter that causes the transaction to revert if the actual price impact exceeds the caller's specified tolerance.

Scope

• buy(key_id, amount, max_slippage_bps?) and sell(key_id, amount, max_slippage_bps?) updated
• Price impact computed against current curve state before execution
• SlippageExceeded error returned with actual_bps and max_bps when violated
• max_slippage_bps of 0 or absent skips the check (opt-in)
• Impact computed after fee deduction

Acceptance Criteria

• SlippageExceeded returned when impact exceeds max_slippage_bps
• Trade executes when impact is within tolerance
• Omitting max_slippage_bps skips check without error
• actual_bps in error matches true price impact
• Impact computation accounts for fees correctly

ETA

24 hours

[Okorie2000-code]

The issue description is clear, Maintainer I would love to work on this issue

[guptakumarranjeet150]

Hey team,

I would love to take this on. My planned approach:

• Implement Add slippage protection parameter to buy and sell functions with thorough authorization verification and clean data structures.
• Add Soroban test cases checking unauthorized invocations, edge values, and state updates.

Ready to deliver a clean, tested PR within 12–24 hours. Please assign!

[Eeboade]

@Eeboade has applied to work on this issue as part of the Stellar Wave Program's 9th wave.

Hi, kindly assign, i would love to fix

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

[shinorh247]

@shinorh247 has applied to work on this issue as part of the Stellar Wave Program's 9th wave.

Hi maintainer I would like to work on this issue

ℹ️ Repo Maintainers: To accept this application, review their application or assign @shinorh247 to this issue.

[flare-999]

@flare-999 has applied to work on this issue as part of the Stellar Wave Program's 9th wave.

pls assign me

ℹ️ Repo Maintainers: To accept this application, review their application or assign @flare-999 to this issue.

[mysterio123865]

@mysterio123865 has applied to work on this issue as part of the Stellar Wave Program's 9th wave.

Pls assign

ℹ️ Repo Maintainers: To accept this application, review their application or assign @mysterio123865 to this issue.

[Samuel-21-eng]

@Samuel-21-eng has applied to work on this issue as part of the Stellar Wave Program's 9th wave.

I can solve this issue

ℹ️ Repo Maintainers: To accept this application, review their application or assign @Samuel-21-eng to this issue.

[drips-wave]

Congratulations, @Samuel-21-eng! 🎉 Your application was accepted by the repo's maintainers, and the issue is due on September 30, 2026.

🧑‍💻 @Samuel-21-eng: Please resolve the issue such that the repo's maintainers have enough time to review your contribution before the due date. You'll earn Points for completing the issue on-time, which will make you eligible for a share of the Stellar Wave Program's reward pool.

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