Add Loan Extension & Modification to Borrowing Contract

[ONEONUORA]

Component: Contracts (Borrowing) | Effort: 3-4 days | Priority: MEDIUM

Current State

Loans have fixed terms with no modification options.

Missing Functions

Loan modification functions:

• extend_loan() - Extend loan due date
• increase_loan_amount() - Borrow more against same collateral
• modify_loan_terms() - Change interest rate or terms
• get_extension_fee() - Calculate extension fee
• get_max_additional_borrow() - Calculate max additional borrow

Why This Matters

• Flexibility: Borrowers need time extensions
• Growth: Increase loan as collateral appreciates
• User retention: Avoid forcing loan closure
• Revenue: Extension fees generate income

Tasks

• Implement extend_loan() function
  • Validate loan exists and active
  • Calculate extension fee (e.g., 1% of principal)
  • Update due date
  • Collect fee
  • Emit LoanExtended event
• Add increase_loan_amount() function
  • Validate health factor allows more borrowing
  • Calculate max additional amount
  • Update loan principal
  • Transfer additional funds
  • Emit LoanIncreased event
• Implement get_extension_fee() calculation
• Add get_max_additional_borrow() view
• Add extension limits (max 2 extensions per loan)
• Track extension count per loan
• Add tests for loan modifications
• Document modification rules

Acceptance Criteria

• Loans can be extended with fee
• Additional borrowing works correctly
• Health factor validated on increases
• Extension limits enforced
• Tests cover modification scenarios
• Documentation complete