fix: preserve overlapping import deduplication

backend/src/services/import.integration.test.ts

@@ -13,6 +13,15 @@ const duplicateStatement = {
   statement: { accountNumber: 'fingerprint-test', currency: 'RUB', openingBalance: 0, closingBalance: 200, exportedAt: '2026-08-20T12:00:00+03:00' },
   transactions: Array.from({ length: 2 }, () => ({ operationAt: '2026-08-20T00:00:00+03:00', amountSigned: 100, commission: 0, description: 'Пополнение' })),
 };
+const overlapStatement = {
+  ...duplicateStatement,
+  statement: { ...duplicateStatement.statement, accountNumber: 'overlap-test' },
+};
+const singleStatement = {
+  ...overlapStatement,
+  statement: { ...overlapStatement.statement, closingBalance: 100 },
+  transactions: overlapStatement.transactions.slice(0, 1),
+};
 
 async function run(): Promise<void> {
   try {
@@ -34,11 +43,22 @@ async function run(): Promise<void> {
       duplicatesSkipped: 0,
       totalInFile: 2,
     });
+    await importStatement(singleStatement);
+    const overlapResult = await importStatement(overlapStatement);
+    if ('status' in overlapResult) throw new Error(overlapResult.message);
+    assert.deepEqual(overlapResult, {
+      accountId: overlapResult.accountId,
+      isNewAccount: false,
+      accountNumberMasked: 'overla******test',
+      imported: 1,
+      duplicatesSkipped: 1,
+      totalInFile: 2,
+    });
     console.log('import metadata SQL: OK');
   } finally {
-    await pool.query("DELETE FROM transactions WHERE account_id IN (SELECT id FROM accounts WHERE bank = 'TEST' AND account_number IN ('metadata-test', 'fingerprint-test'))");
-    await pool.query("DELETE FROM imports WHERE account_id IN (SELECT id FROM accounts WHERE bank = 'TEST' AND account_number IN ('metadata-test', 'fingerprint-test'))");
-    await pool.query("DELETE FROM accounts WHERE bank = 'TEST' AND account_number IN ('metadata-test', 'fingerprint-test')");
+    await pool.query("DELETE FROM transactions WHERE account_id IN (SELECT id FROM accounts WHERE bank = 'TEST' AND account_number IN ('metadata-test', 'fingerprint-test', 'overlap-test'))");
+    await pool.query("DELETE FROM imports WHERE account_id IN (SELECT id FROM accounts WHERE bank = 'TEST' AND account_number IN ('metadata-test', 'fingerprint-test', 'overlap-test'))");
+    await pool.query("DELETE FROM accounts WHERE bank = 'TEST' AND account_number IN ('metadata-test', 'fingerprint-test', 'overlap-test')");
     await pool.end();
   }
 }

backend/src/services/import.ts

@@ -167,15 +167,6 @@ export async function importStatement(
   const data = body as StatementFile;
   const semErr = validateSemantics(data);
   if (semErr) return semErr;
-  const fallbackFingerprints = new Set<string>();
-  const duplicateFallbackFingerprints = new Set<string>();
-  for (const tx of data.transactions) {
-    if (!tx.sourceId) {
-      const fp = computeFingerprint(data.statement.accountNumber, tx);
-      if (fallbackFingerprints.has(fp)) duplicateFallbackFingerprints.add(fp);
-      fallbackFingerprints.add(fp);
-    }
-  }
 
   const client = await db.connect();
   try {
@@ -232,11 +223,14 @@ export async function importStatement(
 
     // Insert transactions
     const insertedIds: number[] = [];
+    const fallbackFingerprintOccurrences = new Map<string, number>();
 
     for (const [sourcePosition, tx] of data.transactions.entries()) {
       const fallbackFingerprint = computeFingerprint(data.statement.accountNumber, tx);
-      const fp = !tx.sourceId && duplicateFallbackFingerprints.has(fallbackFingerprint)
-        ? computeFingerprint(data.statement.accountNumber, tx, sourcePosition)
+      const occurrence = fallbackFingerprintOccurrences.get(fallbackFingerprint) ?? 0;
+      fallbackFingerprintOccurrences.set(fallbackFingerprint, occurrence + 1);
+      const fp = !tx.sourceId && occurrence > 0
+        ? computeFingerprint(data.statement.accountNumber, tx, occurrence)
         : fallbackFingerprint;
       const isCashbackCommissionImport =
         tx.amountSigned === 0 &&

docs/backlog/api_import.md

@@ -124,7 +124,7 @@ accountNumber|operationAt|amountSigned|commission|normalizedDescription[|sourceP
 ```
 
 - `normalizedDescription` — `description` после `trim`.
-- `sourcePosition` — индекс операции в массиве `transactions`; добавляется, только если одинаковые операции без `sourceId` повторяются в одном файле.
+- `sourcePosition` — порядковый номер повторяющейся операции в массиве `transactions`; добавляется, только если одинаковые операции без `sourceId` повторяются в одном файле.
 - Суммы подставляются в том виде, в котором пришли в JSON (числовое представление).
 - Разделитель `|` исключает коллизии при склейке полей разной длины.