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fix(lending): let repay-all clear a crypto loan when the wallet misses only dust

Merged Khanh Pham requested to merge fix/lending-repay-max-wallet-short into develop

Problem

Found on staging while preparing the client test: borrow 0.001 ETH, then "Pay now / repay all" (max: true). Interest makes the debt 0.0010000003 while the wallet holds exactly 0.001, so the repay died with a raw 400 Lending journal would drive USER_CRYPTO(...) negative. A borrower who only holds the principal could never clear a crypto loan with repay-all.

Fix

  • Crypto max repay: when the wallet is short and capacity - round_down(wallet) < debtDust[symbol], repay the wallet balance; settlement's existing DUST write-off clears the remainder. Anything larger is refused (no use of the forgive cap, which could be farmed).
  • Crypto wallet-short failures now return 409 INSUFFICIENT_WALLET_BALANCE (already handled by the FE), like the fiat rail.
  • Wallet row read under lock via LendingJournalService.lockUserWalletBalance (same pair inversion as SupplyService.requestSupply).

Tests

repay.postgres.spec.ts 38/38, borrow.postgres.spec.ts 40/40 (throwaway DB), eslint + build clean, mutation-checked.

Review gate (Opus): PASS after 2 rounds (round 1 removed the forgive-cap branch).

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