fix(frontend): keep scrolled-in transaction history across the periodic refresh

src/frontend/src/eth/services/eth-transactions.services.ts

@@ -79,6 +79,9 @@ export const reloadEthereumTransactions = (params: {
 	silent?: boolean;
 }): Promise<ResultSuccess> => loadEthereumTransactions({ ...params, updateOnly: true });
 
+const hasStoredEthTransactions = (tokenId: TokenId): boolean =>
+	(get(ethTransactionsStore)?.[tokenId] ?? []).length > 0;
+
 const maxEthNativeBlockNumberInStore = (tokenId: TokenId): number | undefined => {
 	const rows = get(ethTransactionsStore)?.[tokenId];
 
@@ -183,8 +186,10 @@ const loadEthTransactions = async ({
 			? await loadEthUserTransactions({ identity, tokenId: transactionTokenId })
 			: undefined;
 
-		// Left alone on a reload: the timer must not rewind pages the user has already scrolled past.
-		if (!updateOnly) {
+		// Only while the list is being built from scratch. The periodic refresh comes through here too,
+		// so resetting the cursor unconditionally would send the next scroll back over pages the user
+		// already has.
+		if (!hasStoredEthTransactions(tokenId)) {
 			setEthBackendPaginationCursor({ tokenId, nextStart: stored?.nextStart });
 		}
 
@@ -215,7 +220,10 @@ const loadEthTransactions = async ({
 				ethTransactionsStore.update({ tokenId, transaction })
 			);
 		} else {
-			ethTransactionsStore.set({ tokenId, transactions: certifiedTransactions });
+			// Prepended rather than set, because this batch is not the whole history: it is the newest
+			// stored page plus whatever is newer than it. Replacing the slot would throw away every older
+			// page the user scrolled in - and the periodic refresh runs through here every 30 seconds.
+			ethTransactionsStore.prepend({ tokenId, transactions: certifiedTransactions });
 		}
 
 		// Save newly finalized transactions to backend (fire-and-forget).

src/frontend/src/tests/eth/services/eth-transactions.services.spec.ts

@@ -557,7 +557,14 @@ describe('eth-transactions.services', () => {
 				});
 			});
 
-			it('should leave the backend cursor alone on a reload', async () => {
+			it('should leave the backend cursor alone once the list has been built', async () => {
+				// The periodic refresh runs the same path, so it must not send the next scroll back over
+				// pages the user already has.
+				ethTransactionsStore.set({
+					tokenId: mockTokenId,
+					transactions: createMockEthTransactions(3).map((data) => ({ data, certified: false }))
+				});
+
 				vi.mocked(loadEthUserTransactions).mockResolvedValue({
 					transactions: createMockEthTransactions(2),
 					newestBlockIndex: 100n,
@@ -574,13 +581,53 @@ describe('eth-transactions.services', () => {
 					networkId: mockNetworkId,
 					tokenId: mockTokenId,
 					chainId: mockChainId,
-					standard: mockStandard,
-					updateOnly: true
+					standard: mockStandard
 				});
 
 				expect(setEthBackendPaginationCursor).not.toHaveBeenCalled();
 			});
 
+			it('should keep pages already scrolled in when it refreshes', async () => {
+				const pagedIn = createMockEthTransactions(4);
+
+				ethTransactionsStore.set({
+					tokenId: mockTokenId,
+					transactions: pagedIn.map((data) => ({ data, certified: false }))
+				});
+
+				// A refresh only ever returns the newest stored page plus anything newer than it.
+				const newestPage = createMockEthTransactions(2);
+
+				vi.mocked(loadEthUserTransactions).mockResolvedValue({
+					transactions: newestPage,
+					newestBlockIndex: 100n,
+					oldestBlockIndex: 50n,
+					nextStart: 60n,
+					totalStored: 30n
+				});
+
+				infuraMocks.mockInfuraGetBlockNumber.mockResolvedValueOnce(150);
+				mockEthTransactionsProvider.mockResolvedValueOnce([]);
+
+				await loadEthereumTransactions({
+					identity: mockIdentity,
+					networkId: mockNetworkId,
+					tokenId: mockTokenId,
+					chainId: mockChainId,
+					standard: mockStandard
+				});
+
+				const rows = get(ethTransactionsStore)?.[mockTokenId];
+
+				assertNonNullish(rows);
+
+				expect(rows).toHaveLength(pagedIn.length + newestPage.length);
+
+				expect(rows.map(({ data: { hash } }) => hash)).toEqual(
+					expect.arrayContaining(pagedIn.map(({ hash }) => hash))
+				);
+			});
+
 			it('should use update method when updateOnly is true', async () => {
 				vi.mocked(loadEthUserTransactions).mockResolvedValue(undefined);