feat: Create ToastService and add unit tests

[Cal-L]

Description

The purpose of these changes is to extend the functionality of triggering the global Toast UI from services. In other words, with these changes, you can now show a toast from non-components by leveraging the ToastService. Example usage is ToastService.showToast or ToastService.closeToast.

Changelog

CHANGELOG entry:

Related issues

Fixes: #25463

Manual testing steps

• Refer to unit tests since ToastService is not yet in use

Screenshots/Recordings

Before

After

Pre-merge author checklist

• I've followed MetaMask Contributor Docs and MetaMask Mobile Coding Standards.
• I've completed the PR template to the best of my ability
• I've included tests if applicable
• I've documented my code using JSDoc format if applicable
• I've applied the right labels on the PR (see labeling guidelines). Not required for external contributors.

Pre-merge reviewer checklist

• I've manually tested the PR (e.g. pull and build branch, run the app, test code being changed).
• I confirm that this PR addresses all acceptance criteria described in the ticket it closes and includes the necessary testing evidence such as recordings and or screenshots.

---

Note

Medium Risk
Introduces a global singleton that stores a React ref and throws/logs when unavailable, which can affect app-wide toast behavior if registration timing or lifecycle is off. Scope is otherwise small and covered by unit tests.

Overview
Enables triggering the global Toast UI from non-React code by adding a new core/ToastService singleton with showToast/closeToast APIs that proxy through a stored toast ref (and log+throw when the ref is missing).

Updates ToastContextWrapper to register its toastRef with ToastService on mount, and adds unit tests covering ref management, proxy behavior, and error paths.

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Cursor Bugbot has reviewed your changes and found 2 potential issues.

[github-actions]

🔍 Smart E2E Test Selection

• Selected E2E tags: SmokeAccounts, SmokeConfirmationsRedesigned
• Selected Performance tags: None (no tests recommended)
• Risk Level: low
• AI Confidence: 80%

click to see 🤖 AI reasoning details

E2E Test Selection:
This PR introduces a new ToastService that allows showing toast notifications from non-React code (controllers, services). The changes include:

1. A new ToastService class with showToast() and closeToast() methods
2. Unit tests for the service
3. A small modification to Toast.context.tsx to register the toast ref with the new service via useEffect

The risk is low because:

• This is primarily a new feature addition, not modifying existing behavior
• The existing ToastContext pattern continues to work unchanged
• The new useEffect in ToastContextWrapper only registers the ref with the service
• The ToastService is not yet being consumed anywhere in the codebase

However, since the ToastContextWrapper wraps the entire app (used in Root/index.tsx) and toasts are used across many features (accounts, permissions, predictions, perps, confirmations), I'm selecting SmokeAccounts and SmokeConfirmationsRedesigned to verify core toast functionality still works. These tags cover account-related toasts (address copying, account switching) and confirmation-related toasts which are common use cases.

Performance Test Selection:
This change introduces a new ToastService for showing toasts from non-React code. The modification to Toast.context.tsx only adds a useEffect hook to register a ref - this is a minimal change that doesn't affect rendering performance, data loading, or any critical user flows. The service itself is not yet being consumed anywhere, so there's no performance impact to measure.

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[codecov-commenter]

Codecov Report

❌ Patch coverage is 86.66667% with 2 lines in your changes missing coverage. Please review.
✅ Project coverage is 75.45%. Comparing base (7e6bee4) to head (7c2803c).
⚠️ Report is 2 commits behind head on main.

Files with missing lines	Patch %	Lines
...mponent-library/components/Toast/Toast.context.tsx	0.00%	2 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main   #25464      +/-   ##
==========================================
- Coverage   80.28%   75.45%   -4.83%     
==========================================
  Files        4260     4261       +1     
  Lines      110124   110173      +49     
  Branches    23477    23475       -2     
==========================================
- Hits        88409    83130    -5279     
- Misses      15506    21015    +5509     
+ Partials     6209     6028     -181     

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[sonarqubecloud]

Quality Gate passed

Issues
1 New issue
0 Accepted issues

Measures
0 Security Hotspots
88.2% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarQube Cloud