Add err.rs error-code stability test asserting frozen client-facing numbers

[greatest0fallt1me]

Description

err.rs defines many error variants whose numeric codes are part of the client-facing API. Add a snapshot test that asserts a frozen mapping of variant name to numeric code so accidental reordering or insertion in the middle of the enum causes the CI to fail loudly.

Requirements and Context

• Snapshot table in a test file
• Adding a new variant requires explicitly extending the table
• Removing a variant fails the test
• 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/err-code-stability-snapshot

2. Implement changes
   • contracts/predictify-hybrid/src/tests/err_code_stability_tests.rs
3. Test and commit
   • cargo test -p predictify-hybrid err_code_stability
   • Cover edge cases
   • Include test output and notes in the PR

Example commit message

test: freeze err.rs error-code snapshot for client stability

Acceptance Criteria

• All current Error variants are in the snapshot
• CI fails on insertion-in-middle of enum
• Doc string explains the policy

Guidelines

• NatSpec-style /// doc comments where relevant
• Clear documentation and inline comments
• Timeframe: 96 hours

[laxjovial]

@laxjovial has applied to work on this issue as part of the Stellar Wave Program's 6th wave.

Please assign. This is a good fix for me

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

[drips-wave]

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

🧑‍💻 @laxjovial: 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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