Partial-fill matching on loan marketplace

[nanaf6203-bit]

Problem Statement

A borrower requesting 100 cannot accept 50 from one lender.

Why it matters

Liquidity fragmentation.

Technical Context

Allow fractional offers + automated best-of matching.

Expected Outcome

Partial accept.

Acceptance Criteria

1. Matching algorithm documented.
2. Tests.
3. Kani harness.
4. SDK.

Implementation Notes

Order-book logic.

Files or modules likely to be affected

contracts/lending/src/lib.rs.

Dependencies

None.

Difficulty level

MEDIUM.

Estimated effort

L (~3 days).