Implement dynamic jump-rate curve in lending pool

[nanaf6203-bit]

Problem Statement

Today: linear (utilisation / 50). Realistic lending uses piecewise jump rates.

Why it matters

Competitive with industry expectations.

Technical Context

Replace with kink at 80%, slope 2x above kink; configurable per pool.

Expected Outcome

Kink-based rate curve.

Acceptance Criteria

1. Property tests around kink.
2. SDK helpers.
3. Docs show formula.
4. Backwards compatible default.
5. Kani harness.

Implementation Notes

Math refactor.

Files or modules likely to be affected

contracts/lending/src/lib.rs.

Dependencies

None.

Difficulty level

HARD.

Estimated effort

L (~1 week).

[yesi3]

@yesi3 has applied to work on this issue as part of the Stellar Wave Program's 7th wave.

Hello Maintainer, I'd like to work on this issue.

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[codenerde]

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

I will work here

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[garfieldxxx1]

@garfieldxxx1 has applied to work on this issue as part of the Stellar Wave Program's 7th wave.

Good day Big Dev! Pls I would love to work on this issue carefully and make PR today

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[cokehill]

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

Hi! I’m a full-stack developer with a strong blockchain background. I’d love to handle this issue and can deliver a clean, reliable solution. Kindly assign it to me.

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

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