test: E2E coverage for toasts, error overlay, selection toolbox, linear mode (#9555)

## Summary

Add 26 E2E tests across 5 spec files covering high-impact,
frequently-used UI flows: toast notifications, error overlay navigation,
selection toolbox actions, linear mode layout, and selection rectangle
multi-select.

## Tests

| Spec file | Tests | Coverage |
|---|---|---|
| `toastNotifications.spec.ts` | 5 | Toast lifecycle, dismiss, severity
levels |
| `errorOverlaySeeErrors.spec.ts` | 6 | Error overlay → errors panel
navigation flow |
| `selectionToolboxActions.spec.ts` | 4 | Delete, info,
convert-to-subgraph, multi-delete |
| `linearMode.spec.ts` | 5 | Linear layout toggle, widget rendering,
persistence |
| `selectionRectangle.spec.ts` | 6 | Vue node multi-selection via
rectangle drag |

## Review Focus

- Selection toolbox tests use `force: true` clicks due to CSS transform
positioning — is this acceptable or should we find a more robust
approach?
- 2 additional toolbox tests (bypass, refresh) were split to draft PR
#9768 due to flaky CI visibility issues with
`useSelectionToolboxPosition`.

## Stack

Depends on #9554 for FeatureFlagHelper/QueueHelper infrastructure.

- #9554: Test infrastructure helpers
- **→ This PR**: Toasts, error overlay, selection toolbox, linear mode,
selection rectangle
- #9556: Node search, bottom panel, focus mode, job history, side panel
- #9557: Errors tab, node headers, queue notifications, settings sidebar
- #9558: Minimap, widget copy, floating menus, node library essentials

---------

Co-authored-by: GitHub Action <action@github.com>

browser_tests/tests/errorOverlaySeeErrors.spec.ts

@@ -0,0 +1,92 @@
+import type { Page } from '@playwright/test'
+
+import {
+  comfyPageFixture as test,
+  comfyExpect as expect
+} from '../fixtures/ComfyPage'
+
+test.describe('Error overlay See Errors flow', { tag: '@ui' }, () => {
+  test.beforeEach(async ({ comfyPage }) => {
+    await comfyPage.settings.setSetting('Comfy.UseNewMenu', 'Top')
+    await comfyPage.settings.setSetting(
+      'Comfy.RightSidePanel.ShowErrorsTab',
+      true
+    )
+    await comfyPage.setup()
+  })
+
+  async function triggerExecutionError(comfyPage: {
+    canvasOps: { disconnectEdge: () => Promise<void> }
+    page: Page
+    command: { executeCommand: (cmd: string) => Promise<void> }
+  }) {
+    await comfyPage.canvasOps.disconnectEdge()
+    await comfyPage.page.keyboard.press('Escape')
+    await comfyPage.command.executeCommand('Comfy.QueuePrompt')
+  }
+
+  test('Error overlay appears on execution error', async ({ comfyPage }) => {
+    await triggerExecutionError(comfyPage)
+
+    await expect(
+      comfyPage.page.locator('[data-testid="error-overlay"]')
+    ).toBeVisible()
+  })
+
+  test('Error overlay shows error message', async ({ comfyPage }) => {
+    await triggerExecutionError(comfyPage)
+
+    const overlay = comfyPage.page.locator('[data-testid="error-overlay"]')
+    await expect(overlay).toBeVisible()
+    await expect(overlay).toHaveText(/\S/)
+  })
+
+  test('"See Errors" opens right side panel', async ({ comfyPage }) => {
+    await triggerExecutionError(comfyPage)
+
+    const overlay = comfyPage.page.locator('[data-testid="error-overlay"]')
+    await expect(overlay).toBeVisible()
+
+    await overlay.getByRole('button', { name: /See Errors/i }).click()
+
+    await expect(comfyPage.page.getByTestId('properties-panel')).toBeVisible()
+  })
+
+  test('"See Errors" dismisses the overlay', async ({ comfyPage }) => {
+    await triggerExecutionError(comfyPage)
+
+    const overlay = comfyPage.page.locator('[data-testid="error-overlay"]')
+    await expect(overlay).toBeVisible()
+
+    await overlay.getByRole('button', { name: /See Errors/i }).click()
+
+    await expect(overlay).not.toBeVisible()
+  })
+
+  test('"Dismiss" closes overlay without opening panel', async ({
+    comfyPage
+  }) => {
+    await triggerExecutionError(comfyPage)
+
+    const overlay = comfyPage.page.locator('[data-testid="error-overlay"]')
+    await expect(overlay).toBeVisible()
+
+    await overlay.getByRole('button', { name: /Dismiss/i }).click()
+
+    await expect(overlay).not.toBeVisible()
+    await expect(
+      comfyPage.page.getByTestId('properties-panel')
+    ).not.toBeVisible()
+  })
+
+  test('Close button (X) dismisses overlay', async ({ comfyPage }) => {
+    await triggerExecutionError(comfyPage)
+
+    const overlay = comfyPage.page.locator('[data-testid="error-overlay"]')
+    await expect(overlay).toBeVisible()
+
+    await overlay.getByRole('button', { name: /close/i }).click()
+
+    await expect(overlay).not.toBeVisible()
+  })
+})