Implement batch trade endpoint for multi-key order submission

[Chucks1093]

Summary

Build a batch trade endpoint that accepts multiple buy or sell orders, validates each against current key state, and constructs a single batch transaction for the client to sign and submit.

Scope

• POST /trade/batch — accepts orders array with key_id, direction, amount, max_slippage_bps
• Each order validated against current price, slippage, cap, cooldown, and freeze state
• Per-order validation errors returned before transaction construction
• Unsigned batch transaction returned for client signing
• Estimated total fee and cost included in response

Acceptance Criteria

• Per-order validation catches all constraint violations with clear errors
• Unsigned batch transaction constructed correctly for valid orders
• Total fee and cost estimates accurate across all orders
• Mixed valid/invalid order sets return per-order error detail
• Endpoint rejects empty order arrays with 400

ETA

12 hours

[alilans]

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

I bring strong technical skills, problem-solving ability, and a commitment to delivering reliable, high-quality solutions.

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[codetamer]

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Gm maintainer, I'd love to handle this issue! Ready to start right now and submit a clean fix with passing tests within 1-2 hours. Please assign me! 🙏

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[aduagba4133]

@aduagba4133 has applied to work on this issue as part of the Stellar Wave Program's 9th wave.

Hello, I’ve gone through the requirements and I’m confident I can implement a proper solution that matches the acceptance criteria. Kindly assign this issue to me.

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[Damola09]

@Damola09 has applied to work on this issue as part of the Stellar Wave Program's 9th wave.

Can i work on this?

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[drips-wave]

Congratulations, @Damola09! 🎉 Your application was accepted by the repo's maintainers, and the issue is due on September 30, 2026.

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[grantfox-oss]

🎉 This issue has been marked as completed on GrantFox!

@Damola09's PR #990 was approved and merged by @Chucks1093.

🏆 @Damola09: You earned 35 FoxPoints for this contribution! Your current tier: Explorer (389 total points). Track your full progress on GrantFox.

👏 Great work, @Damola09! Keep contributing to accesslayerorg.

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This issue has been completed by @Damola09 as part of the Stellar Wave Program's 9th Wave 🥳

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