fix(bridge): prevent stale token balance showing when switching Solana tokens

[infiniteflower]

Description

When switching between Solana tokens in the Bridge/Swaps UI, selecting a token with zero or undefined balance would incorrectly display the previous token's balance. This was caused by stale state not being cleared when switching tokens, and a truthiness check that failed for "0" balance.

Changelog

CHANGELOG entry: Fixed a bug where switching Solana tokens showed incorrect balance

Related issues

Fixes: SWAPS-3686

Manual testing steps

Feature: Solana token balance display

  Scenario: user switches to a token with zero balance
    Given user is on Bridge/Swaps with Solana network selected
    And user has selected a token with non-zero balance

    When user switches to a different token with zero balance
    Then the balance should show zero (not the previous token's balance)

Screenshots/Recordings

Before

Screen.Recording.2026-01-07.at.4.06.09.PM.mov

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.

[github-actions]

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[github-actions]

🔍 Smart E2E Test Selection

• Selected E2E tags: SmokeTrade
• Risk Level: medium
• AI Confidence: 85%

click to see 🤖 AI reasoning details

The changes are focused on the Bridge UI component and the useLatestBalance hook used in Bridge functionality:

1. TokenInputArea/index.tsx: A small UI fix that changes when error color is displayed for insufficient balance - now only shows error color for source token (not destination). This is a visual-only change.

2. useLatestBalance/index.ts:

   • Adds a new assetId field (CAIP-19 format) to the balance object for consistent token matching
   • Adds logic to reset balance when token changes to prevent stale data
   • Fixes a bug where "0" balance was incorrectly treated as falsy

3. useLatestBalance.test.tsx: Unit test updates to include the new assetId field.

The useLatestBalance hook is used in:

• BridgeView (main bridge view)
• QuoteDetailsCard (bridge quote display)
• SwapsKeypad (swap input)
• useBridgeQuoteRequest (bridge quote requests)

All these are part of the Bridge/Swap functionality. The E2E tests in e2e/specs/swaps/bridge-action-smoke.spec.ts and e2e/specs/swaps/swap-action-smoke.spec.ts are tagged with SmokeTrade and test the bridge and swap flows that would exercise these changes.

The risk is medium because:

• The changes affect balance display and tracking in the bridge flow
• The bug fix for "0" balance handling could affect edge cases
• The changes are well-scoped to Bridge functionality with good unit test coverage

View GitHub Actions results

[sonarqubecloud]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
1 Security Hotspot
97.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarQube Cloud

[infiniteflower]

Closed in favor of #24329