close_credit_line utilization guards

[greatest0fallt1me]

Description

Test and document whether borrower close requires zero utilization and how admin forced close behaves.

Requirements and context

• Match product policy.
• Update state machine docs.

Suggested execution

Fork and branch

Fork the repo and create a branch:

git checkout -b test/close-nonzero-utilization

Implement changes

• Add tests for non-zero utilization close attempts.
• Align close_credit_line implementation if needed.

Test and commit

Run the full test suite, cover edge cases, and include test output plus security notes (assumptions, trust boundaries, failure modes) in the PR description.

Run tests

cargo test -p creditra-credit

Example commit message

test(credit): close_credit_line utilization guards

Guidelines

• Minimum 95% line coverage (cargo llvm-cov as documented in the contracts README).

• Clear documentation (Rust /// doc comments on public items; update docs/credit.md when behavior changes).

• Timeframe: 96 hours.

• Optionally run: cargo llvm-cov --workspace --all-targets --fail-under-lines 95 before merge.

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[rohan911438]

@rohan911438 has applied to work on this issue as part of the Stellar Wave Program's 3rd wave.

Hi, I’d like to work on this issue. I understand the requirements and can start immediately. I’ll ensure a clean, tested implementation and a quick turnaround. Kindly assign this to me.

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Congratulations, @rohan911438! 🎉 Your application was accepted by the repo's maintainers, and the issue is due on March 30, 2026.

🧑‍💻 @rohan911438: 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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