# MI4 - Error/Cancel/Undo Patterns (Snackbar/Toast with Undo)

## Module
Web

## Status
PARTIALLY_IMPLEMENTED

## Description
i18n keys for toast/undo/undoCountdown patterns exist and snackbar usage is present across components. However, a dedicated centralized snackbar/toast service with the specific 8s undo window and aria-live=polite pattern was not found as a standalone component.

## What's Implemented
- **Existing components**:
  - `accordion` (`src/Web/StellaOps.Web/src/app/shared/components/accordion/accordion.component.ts`)
  - `ai-assist-panel` (`src/Web/StellaOps.Web/src/app/shared/components/ai/ai-assist-panel.component.ts`)
  - `ai-authority-badge` (`src/Web/StellaOps.Web/src/app/shared/components/ai/ai-authority-badge.component.ts`)
  - `ai-chip` (`src/Web/StellaOps.Web/src/app/shared/components/ai/ai-chip.component.ts`)
  - `ai-explain-chip` (`src/Web/StellaOps.Web/src/app/shared/components/ai/ai-explain-chip.component.ts`)
  - `ai-exploitability-chip` (`src/Web/StellaOps.Web/src/app/shared/components/ai/ai-exploitability-chip.component.ts`)
  - `ai-fix-chip` (`src/Web/StellaOps.Web/src/app/shared/components/ai/ai-fix-chip.component.ts`)
  - `ai-needs-evidence-chip` (`src/Web/StellaOps.Web/src/app/shared/components/ai/ai-needs-evidence-chip.component.ts`)
  - `ai-summary` (`src/Web/StellaOps.Web/src/app/shared/components/ai/ai-summary.component.ts`)
  - `ai-vex-draft-chip` (`src/Web/StellaOps.Web/src/app/shared/components/ai/ai-vex-draft-chip.component.ts`)
- **Existing services**:
  - `replay` (`src/Web/StellaOps.Web/src/app/shared/components/reproduce/replay.service.ts`)
  - `graph-export` (`src/Web/StellaOps.Web/src/app/shared/services/graph-export.service.ts`)
  - `plain-language` (`src/Web/StellaOps.Web/src/app/shared/services/plain-language.service.ts`)

## What's Missing
- **Centralized snackbar/toast service**: No centralized `ToastService` with the specific 8-second undo window, countdown timer, and `aria-live=polite` pattern
- **Undo action infrastructure**: i18n keys for `toast.undo` and `undoCountdown` exist but no centralized undo action queue that buffers destructive operations for the undo window
- **Cancel pattern standardization**: No consistent cancel pattern across all modal/drawer interactions (some modals lack cancel confirmation for dirty forms)
- **Error boundary component**: No centralized error boundary component that catches and displays user-friendly errors with retry actions

## Implementation Plan
- Create centralized `ToastService` with undo support, 8s countdown, and `aria-live=polite`
- Implement undo action queue for buffering destructive operations
- Standardize cancel patterns across modals and drawers
- Add error boundary component with retry actions

## E2E Test Plan
- **Setup**:
  - [ ] Log in with a user that has appropriate permissions
  - [ ] Navigate to the relevant page/section where this feature appears
  - [ ] Ensure test data exists (scanned artifacts, SBOM data, or seed data as needed)
- **Core verification**:
  - [ ] Verify the component renders correctly with sample data
  - [ ] Verify interactive elements respond to user input
  - [ ] Verify data is fetched and displayed from the correct API endpoints
- **Edge cases**:
  - [ ] Verify graceful handling when backend API is unavailable (error state)
  - [ ] Verify responsive layout at different viewport sizes
  - [ ] Verify accessibility (keyboard navigation, screen reader labels, ARIA attributes)