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Audit finding 9a: a cash refund posted DR AR (control up) while the customer subledger went down — opposite directions, guaranteeing AR drift. Per the chosen model, a cash refund now *reverses the sale*: DR Sales Returns (revenue portion) + DR Sales Tax Payable (tax portion) / CR Bank, with the customer AR balance left untouched (the invoice stays paid; the sale is contra'd). - New 4960 "Sales Returns & Allowances" contra-revenue account (seed + self-heal). - Tax/revenue split centralized in Core RefundAllocation.Split so the posting and both reporting recomputes compute it identically (a mismatch would unbalance the trial balance). - InvoicesController IssueRefund/CancelRefund: new posting + reversal; no AR/ customer-balance change. - LedgerService (per-account + prior balance): refunds debit Sales Returns + Sales Tax, no longer debit AR; bank credit unchanged. - FinancialReportService: trial balance, balance sheet (retained earnings + tax liability), and P&L (contra-revenue line) all updated to match. Store-credit refunds are excluded everywhere (they post via CreditMemo, not the GL — 9b). Verified: $108 refund (incl. $8 tax) -> bank -100... checks: assets -108 = liabilities -8 + equity -100. New tests cover the split invariant and the ledger postings. Build clean; 283 unit tests pass. Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>