fix: improve UX around gas estimation failing

[jpuri]

Description

Improve handling of scenario when gas estimation fails.

Changelog

CHANGELOG entry:

Related issues

Fixes: https://github.com/MetaMask/MetaMask-planning/issues/6389

Manual testing steps

1. Mock gas estimations to fail and submit a transaction
2. Check that Unavailable is displayed for gas
3. Update to custom value and see that alert and unavailable goes away

Screenshots/Recordings

Screen.Recording.2026-02-10.at.8.12.20.PM.mov

Pre-merge author checklist

• I've followed MetaMask Contributor Docs and MetaMask Extension 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
UI/UX and hook refactor around gas-estimation failure handling; limited scope with added test coverage, but touches core confirmation fee display logic.

Overview
Improves confirmation UX when gas estimation fails by introducing a shared useEstimationFailed hook (based on simulationFails, but ignored for UserFeeLevel.CUSTOM) and wiring it into the confirmations flow.

When estimation is failed, the gas fee token selector is disabled (no arrow, modal won’t open) and the gas fee display shows "Unavailable" (new transactions.unavailable i18n string), while still showing Paid by MetaMask for sponsored fees. Tests were updated/added to cover these behaviors and the updated alert suppression for custom fee level.

^{Written by Cursor Bugbot for commit a6ad6aa. This will update automatically on new commits. Configure here.}

[github-actions]

CLA Signature Action: All authors have signed the CLA. You may need to manually re-run the blocking PR check if it doesn't pass in a few minutes.

[github-actions]

🔍 Smart E2E Test Selection

• Selected E2E tags: SmokeConfirmations
• Selected Performance tags: None (no tests recommended)
• Risk Level: medium
• AI Confidence: 85%

click to see 🤖 AI reasoning details

E2E Test Selection:
The changes are focused on the transaction confirmation UI, specifically handling gas estimation failures:

1. New useEstimationFailed hook: A new hook that determines if gas estimation has failed (simulationFails is truthy AND userFeeLevel is not CUSTOM). This is used to improve UX when gas estimation fails.

2. selected-gas-fee-token.tsx: Now disables gas fee token selection when estimation has failed, preventing users from selecting gas fee tokens when gas cannot be accurately estimated.

3. gas-fee-details-row.tsx: Now shows "Unavailable" text when estimation has failed instead of potentially incorrect display values.

4. useGasEstimateFailedAlert.ts: Refactored to use the new centralized hook instead of directly checking simulationFails.

5. locales/languages/en.json: Added "Unavailable" translation string for the transactions section.

The gas-fee-details-row component is used across multiple confirmation types (staking, transaction batch, approve, contract deployment, contract interaction, switch account type, transfer), all of which are covered by SmokeConfirmations.

The changes are defensive improvements to error handling in the confirmation flow - they don't add new features but improve how the app handles edge cases when gas estimation fails. The risk is medium because while the changes are well-scoped with good unit test coverage, they affect a critical user flow (transaction confirmations) and could potentially impact the user's ability to complete transactions if there are any issues.

Performance Test Selection:
The changes are focused on conditional UI rendering based on gas estimation failure state. They don't introduce new data loading, complex computations, list rendering, or changes to app startup/initialization. The changes are simple boolean checks that conditionally show 'Unavailable' text or disable gas fee token selection. No performance impact is expected from these changes.

View GitHub Actions results

[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