feat: Add useMMPayFiatConfig hook and feature flag selector

[OGPoyraz]

Description

• Add selectMetaMaskPayFiatFlags selector to read the confirmations_pay_fiat LaunchDarkly flag, gating the upcoming fiat payment option in transaction confirmations
• Add useMMPayFiatConfig hook for React components to consume the flag
• Flag defaults to disabled - no UI or behavioral changes until downstream tasks wire it in

Changelog

CHANGELOG entry:

Related issues

Fixes: #27110

Manual testing steps

Feature: my feature name

  Scenario: user [verb for user action]
    Given [describe expected initial app state]

    When user [verb for user action]
    Then [describe expected outcome]

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

Low Risk
Low risk: adds a new feature-flag selector/hook with a disabled-by-default fallback and unit tests, without changing existing app behavior.

Overview
Adds support for gating upcoming fiat payments in confirmations by introducing a new confirmations_pay_fiat remote flag.

This PR adds selectMetaMaskPayFiatFlags (with PAY_FIAT_ENABLED_DEFAULT = false) plus a small useMMPayFiatConfig React hook to consume it, and includes unit tests covering default/flagged behavior.

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[github-actions]

🔍 Smart E2E Test Selection

• Selected E2E tags: SmokeConfirmations
• Selected Performance tags: None (no tests recommended)
• Risk Level: low
• AI Confidence: 90%

click to see 🤖 AI reasoning details

E2E Test Selection:
The changes add new feature flag infrastructure for a "Pay Fiat" feature in the confirmations domain:

1. A new selector selectMetaMaskPayFiatFlags is added to read the confirmations_pay_fiat remote feature flag
2. A new React hook useMMPayFiatConfig wraps this selector for component use
3. Both have comprehensive unit tests

Key observations:

• These are purely additive changes - no existing code is modified
• The new selector and hook are NOT yet consumed by any other code in the codebase (verified via grep)
• The feature flag defaults to false (disabled)
• The changes are in the confirmations hooks/selectors directory

Since the changes are in the confirmations domain and add new feature flag infrastructure that could affect confirmations behavior when enabled in the future, running SmokeConfirmations provides reasonable validation that the confirmations infrastructure still works correctly. However, since nothing currently consumes these new exports, the risk is very low.

Performance Test Selection:
These changes add new feature flag selectors and hooks that are not yet consumed by any components. The changes are purely additive infrastructure code with no impact on UI rendering, data loading, or any user-facing flows. No performance tests are needed.

View GitHub Actions results

[github-actions]

⚠️ E2E Fixture Validation — Structural changes detected

Category	Count
New keys	68
Missing keys	11
Type mismatches	0
Value mismatches	7 (informational)

The committed fixture schema is out of date. To update, comment:

@metamaskbot update-mobile-fixture

View full details | Download diff report

[sonarqubecloud]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
100.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarQube Cloud