Add ContractError stability test for markets (v7)

[greatest0fallt1me]

Description

This is a smart-contract issue for the GrantFox campaign. This is a smart-contract issue for the GrantFox FWC26 campaign (Stellar Wave). Freeze client-facing error code numbers for markets.

Requirements and Context

• Implement per the description
• Add focused tests
• Document any API/visible changes
• Adhere to repo's lint and code style
• Must be secure, tested, and documented
• Should be efficient and easy to review

Suggested Execution

1. Fork the repo and create a branch

   git checkout -b task/markets-errstab-v7

2. Implement changes
   • contracts/markets/tests/err_stab.rs
3. Test and commit
   • Run the repo's standard test suite and lint
   • Cover edge cases; include output in the PR

Example commit message

test: markets err stability

Acceptance Criteria

• Implementation matches the description
• Tests added and passing
• Code review approved
• Docs updated

Guidelines

• Minimum 95% test coverage with cargo test
• require_auth on every state-changing entrypoint
• Overflow-safe math; no unwrap() in production paths
• Clear NatSpec-style /// rustdoc
• Timeframe: 96 hours

[ositaemmanuel653-netizen]

@ositaemmanuel653-netizen has applied to work on this issue as part of the Stellar Wave Program's 7th wave.

Hello big dev please allow me take on this issue.

ℹ️ Repo Maintainers: To accept this application, review their application or assign @ositaemmanuel653-netizen to this issue.

[drips-wave]

Congratulations, @ositaemmanuel653-netizen! 🎉 Your application was accepted by the repo's maintainers, and the issue is due on July 30, 2026.

🧑‍💻 @ositaemmanuel653-netizen: 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.

Warning

When opening a PR, please link it to this issue to ensure it gets tracked accurately. Points are awarded when this issue is marked as completed by the maintainer.

🤠 Repo maintainers: Please keep an eye on the contributor's progress and review their work before the due date. You can manage this issue, including adjusting its complexity and points, here.

🌊 Happy Wave 🌊

[greatest0fallt1me]

Hey @ositaemmanuel653-netizen 👋 — you've been assigned to this issue based on your DripsWave application.

Quick reminders:

• Draft PR early and link with Closes #<issue-number> so DripsWave auto-closes.
• Please respect the 4 assignments per org cap (DripsWave auto-unassigns beyond).
• Ping in Discord for help: https://discord.gg/WC53JxDqx

Looking forward to your PR — good luck! 🚀

[drips-wave]

This issue has been completed by @ositaemmanuel653-netizen as part of the Stellar Wave Program's 7th Wave 🥳

😎 @ositaemmanuel653-netizen: You earned 100 Points for completing this issue! After the current Wave ends, you'll be eligible for a percentage of the Wave's reward pool based on the percentage of total points you've earned. Learn more here. You can also Leave a review to share your experience working on this issue.

🧑‍💻 Repo maintainers: How'd the contributor do? Leave a review to share your experience working with them.