Fix duplicate transaction updates in Find & Replace

- Add deduplication logic to prevent duplicate updates when multiple members of a split transaction are selected
- Add comprehensive tests for applyFindReplace function
- Fixes issue where selecting parent and children of split transactions caused duplicates

Co-authored-by: MatissJanis <886567+MatissJanis@users.noreply.github.com>

packages/desktop-client/src/hooks/useTransactionBatchActions.ts

@@ -175,7 +175,21 @@ export function useTransactionBatchActions() {
           : diff.added;
       });
 
-      await send('transactions-batch-update', changes);
+      // Deduplicate changes by ID to prevent duplicate updates when
+      // multiple members of a split transaction are selected
+      const deduplicatedChanges: Diff<TransactionEntity> = {
+        added: Array.from(
+          new Map(changes.added?.map(item => [item.id, item])).values(),
+        ),
+        updated: Array.from(
+          new Map(changes.updated?.map(item => [item.id, item])).values(),
+        ),
+        deleted: Array.from(
+          new Map(changes.deleted?.map(item => [item.id, item])).values(),
+        ),
+      };
+
+      await send('transactions-batch-update', deduplicatedChanges);
 
       onSuccess?.(ids, name, value, mode);
     };

packages/loot-core/src/shared/util.test.ts

@@ -1,4 +1,5 @@
 import {
+  applyFindReplace,
   currencyToAmount,
   getNumberFormat,
   looselyParseAmount,
@@ -229,3 +230,38 @@ describe('utility functions', () => {
     expect(stringToInteger('−3')).toBe(-3);
   });
 });
+
+describe('applyFindReplace', () => {
+  test('basic string replacement works', () => {
+    expect(applyFindReplace('hello world', 'world', 'universe', false)).toBe(
+      'hello universe',
+    );
+    expect(applyFindReplace('test test test', 'test', 'demo', false)).toBe(
+      'demo demo demo',
+    );
+  });
+
+  test('handles null and empty values', () => {
+    expect(applyFindReplace(null, 'test', 'replace', false)).toBe('');
+    expect(applyFindReplace(undefined, 'test', 'replace', false)).toBe('');
+    expect(applyFindReplace('', 'test', 'replace', false)).toBe('');
+    expect(applyFindReplace('hello', '', 'replace', false)).toBe('hello');
+  });
+
+  test('regex replacement works', () => {
+    expect(applyFindReplace('test123', '\\d+', 'NUM', true)).toBe('testNUM');
+    expect(applyFindReplace('foo bar baz', 'b\\w+', 'word', true)).toBe(
+      'foo word word',
+    );
+  });
+
+  test('handles invalid regex gracefully', () => {
+    expect(applyFindReplace('test', '[invalid', 'replace', true)).toBe('test');
+  });
+
+  test('case-sensitive replacement', () => {
+    expect(applyFindReplace('Test test TEST', 'test', 'demo', false)).toBe(
+      'Test demo TEST',
+    );
+  });
+});