diff --git a/e2e/b-ui.spec.js b/e2e/b-ui.spec.js
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+// B-UI: functional behavior of shared primitives that axe/a11y can't assert —
+// dialogs cancel without side effects, Selects open by mouse and keyboard,
+// disabled controls stay inert. All checks are READ-ONLY (Esc/Cancel/reopen), so
+// they're safe alongside the other UI specs in the parallel suite.
+const { test, expect } = require('@playwright/test');
+const { STORAGE_STATE } = require('./constants');
+
+test.use({ storageState: STORAGE_STATE });
+
+test('dialog: Add Bill opens, Esc closes it, and creates nothing (Cancel = no side effect)', async ({ page }) => {
+  await page.goto('/');
+  const badges = page.locator('button[title="Click to mark paid"]:visible, button[title="Click to mark unpaid"]:visible');
+  await expect(badges.first()).toBeVisible(); // wait for bills to load before counting
+  const before = await badges.count();
+
+  await page.getByRole('button', { name: 'Add Bill' }).click();
+  const dialog = page.getByRole('dialog');
+  await expect(dialog).toBeVisible();
+  // Focus moved into the dialog (focus trap).
+  await expect(dialog.locator(':focus')).toHaveCount(1);
+
+  await page.keyboard.press('Escape');
+  await expect(dialog).toBeHidden();
+  // No bill was created and the page is still functional.
+  await expect(page.getByRole('button', { name: 'Add Bill' })).toBeVisible();
+  await expect.poll(() => badges.count()).toBe(before);
+});
+
+test('select: category filter opens by mouse and by keyboard and lists options', async ({ page, isMobile }) => {
+  test.skip(isMobile, 'filter panel layout differs on mobile');
+  await page.goto('/');
+
+  // Radix Select trigger exposes role="combobox".
+  const trigger = page.getByRole('combobox', { name: 'Filter by category' });
+  await expect(trigger).toBeVisible();
+
+  // Mouse: opens a listbox with the "All categories" option.
+  await trigger.click();
+  const listbox = page.getByRole('listbox');
+  await expect(listbox).toBeVisible();
+  await expect(page.getByRole('option', { name: 'All categories' })).toBeVisible();
+  await page.keyboard.press('Escape');
+  await expect(listbox).toBeHidden();
+
+  // Keyboard: focus the trigger and open with Enter.
+  await trigger.focus();
+  await page.keyboard.press('Enter');
+  await expect(page.getByRole('listbox')).toBeVisible();
+  await page.keyboard.press('Escape');
+});
+
+test('disabled control: sort-direction button is inert in Custom order', async ({ page, isMobile }) => {
+  test.skip(isMobile, 'filter panel layout differs on mobile');
+  await page.goto('/');
+  // Default sort is "Custom order", for which the asc/desc toggle is disabled.
+  const dir = page.getByRole('button', { name: 'Asc' });
+  await expect(dir).toBeVisible();
+  await expect(dir).toBeDisabled();
+  // Clicking a disabled control must be a no-op (force past the actionability guard).
+  await dir.click({ force: true });
+  await expect(dir).toBeDisabled();
+});