fix: populate settlementVia.preImage in lnInvoicePaymentSend response

[blink-claw-bot]

Closes #506

Problem

The lnInvoicePaymentSend GraphQL mutation was returning null for settlementVia.preImage even when Lightning payments succeeded. This was due to a race condition where:

1. After a successful LND payment, lockedPaymentViaLnSteps calls LedgerFacade.updateMetadataByHash() to persist the preimage
2. Then executePaymentViaLn calls getTransactionForWalletByJournalId to fetch the wallet transaction
3. However, in helpers.ts, persistAndReturnEntry does NOT await txMetadataRepo.persistAll() (fire-and-forget)
4. So when updateMetadataByHash runs, the metadata documents may not exist yet, causing modifiedCount: 0 → NoTransactionToUpdateError
5. The error is silently ignored, so the preimage is never persisted

Root Cause Analysis

The race condition occurs in core/api/src/services/ledger/helpers.ts line 28 where txMetadataRepo.persistAll() is called without await.

Solution

This PR implements two fixes:

Primary Fix: Direct PreImage Injection

• Modified LnSendAttemptResult.ok() to accept an optional revealedPreImage parameter
• Updated the type definitions to include the preimage field
• In lockedPaymentViaLnSteps, pass the payResult.revealedPreImage to LnSendAttemptResult.ok()
• In executePaymentViaLn, inject the preImage directly into the wallet transaction's settlementVia before returning

Secondary Fix: Race Condition

• Added await to txMetadataRepo.persistAll() in helpers.ts to prevent the race condition

Testing

• TypeScript compilation passes (pnpm tsc --noEmit)
• All changes are surgical, minimal edits to existing code
• Preserves existing functionality while fixing the bug

Files Modified

• core/api/src/app/payments/send-lightning.ts — main fix
• core/api/src/app/payments/ln-send-result.ts — result type update
• core/api/src/app/payments/index.types.d.ts — type definitions
• core/api/src/services/ledger/helpers.ts — race condition fix

🤖 PR by claude-sonnet-4 via Blink-Claw-Bot