Fix bulk code vendor pre-population for single vs multi-client contexts

- vendor-default-account now uses raw vendor default account (not client-specific override)
- Account name is clientized via d-accounts/clientize only for single-client contexts
- Added single-client-id helper that returns client ID only when user has exactly one client
- Added multi-client e2e test verifying no pre-population across multiple clients
- Updated test server to support multi-client mode switching via /test-set-client-mode
- Test server now seeds a second client for multi-client scenarios

e2e/bulk-code-transactions.spec.ts

@@ -8,7 +8,10 @@ async function getTestInfo(page: any) {
   return testInfoCache;
 }
 
-async function navigateToTransactions(page: any) {
+async function navigateToTransactions(page: any, clientMode: string = 'mine') {
+  await page.setExtraHTTPHeaders({
+    'x-clients': clientMode === 'all' ? '"all"' : '"mine"'
+  });
   await page.goto('/transaction2');
   await page.waitForSelector('table tbody tr');
 }
@@ -387,6 +390,9 @@ test.describe('Bulk Code Transactions - Account Distribution', () => {
 
 test.describe('Bulk Code Transactions - Vendor Pre-population', () => {
   test('should pre-populate default account when vendor is selected', async ({ page }) => {
+    // Ensure single-client mode
+    await page.request.get('/test-set-client-mode?mode=single-client');
+    
     await navigateToTransactions(page);
     await selectTransactionByIndex(page, 0);
     await openBulkCodeModal(page);
@@ -440,4 +446,48 @@ test.describe('Bulk Code Transactions - Vendor Pre-population', () => {
     
     await page.waitForSelector('table tbody tr');
   });
+  
+  test('should NOT pre-populate default account when user has multiple clients', async ({ page }) => {
+    // Switch to multi-client mode
+    await page.request.get('/test-set-client-mode?mode=multi-client');
+    
+    // Use 'all' to see all clients in the database
+    await navigateToTransactions(page, 'all');
+    await selectTransactionByIndex(page, 0);
+    await openBulkCodeModal(page);
+    
+    // Select vendor
+    const testInfo = await getTestInfo(page);
+    const vendorId = testInfo.accounts.vendor;
+    
+    const vendorContainer = page.locator('div[hx-post*="vendor-changed"]').first();
+    const vendorHidden = vendorContainer.locator('input[type="hidden"]').first();
+    
+    await vendorHidden.evaluate((el: HTMLInputElement, value: string) => {
+      const newInput = document.createElement('input');
+      newInput.type = 'hidden';
+      newInput.name = el.name;
+      newInput.value = value;
+      el.parentNode.replaceChild(newInput, el);
+    }, vendorId.toString());
+    
+    // Dispatch change on the container to trigger HTMX
+    await vendorContainer.evaluate((el: HTMLElement) => {
+      el.dispatchEvent(new Event('change', { bubbles: true }));
+    });
+    
+    // Wait for HTMX response
+    await page.waitForResponse(response => response.url().includes('/vendor-changed') && response.status() === 200);
+    await page.waitForTimeout(500);
+    
+    // Should NOT have pre-populated account rows - only the "New account" button row
+    const accountRows = page.locator('#account-entries tbody tr');
+    const rowCount = await accountRows.count();
+    
+    // With multi-client, no pre-population should happen, so only 1 row (the "New account" button)
+    expect(rowCount).toBe(1);
+    
+    // Switch back to single-client mode for other tests
+    await page.request.get('/test-set-client-mode?mode=single-client');
+  });
 });