cherry-pick 29968: fix: handle null STX status containing pre-enabled…

… state (#30010)

cherry-picks #29968

## **Description**

Only remaining QA issue for feature: [[EXT] STX Banner Alert & STX x
Default
Migration](#28854)

Update migration to treat null preference value as an existing enabled
state, preventing unneeded banner display for v12.6.0-12.7.2 migrations.

The update removes the `null` check in the migration's `transformState`
function (near line 46 of `135.ts`)

```ts
  if (
    currentOptInStatus === undefined ||
    currentOptInStatus === null ||  // remove this line
    (currentOptInStatus === false && !hasExistingSmartTransactions(state))
  ) {
  ```

And let the condition fall through to the else block. This will ensure that `smartTransactionsMigrationApplied: false` and ensure that we don't see a banner on Transaction Confirmation.

[![Open in GitHub Codespaces](https://github.com/codespaces/badge.svg)](https://codespaces.new/MetaMask/metamask-extension/pull/29968?quickstart=1)

## **Related issues**

Fixes: #29970  

**Description**
Migration fails when the origin extension is version 12.7.x (tested 1 and 2)
In this cases, the alert banner is displayed in the confirmation screen (e.g: send and swaps) when the parameter STX in settings was enabled in the older extension.

**Expected behavior**
The behaviour should be:
extension 12.11.0 < with STX activated -> update to 12.11.0 and no banner is displayed in the confirmation screen

## **Manual testing steps for fix**

1. Migrate from any version 12.6.* to 12.7.* to 12.10.1 (or 12.11.0 depending) 
2. Ensure that STX is ON in the old version (before migrating to the newer version)
3. After migration try to Swap or Send on Ethereum Mainnet  & Sepolia and ensure there is no STX Banner Alert shown

## **Screenshots/Recordings**

For users with STX ON before and after Migration:

### **Before**

<img width="150" alt="after-fix" src="https://github.com/user-attachments/assets/fe33da33-7828-45e2-b7a1-8b7d60b12de5" />

### **After**

<img width="150" alt="after-fix" src="https://github.com/user-attachments/assets/fe33da33-7828-45e2-b7a1-8b7d60b12de5" />

## **Pre-merge author checklist**

- [x] I've followed [MetaMask Contributor Docs](https://github.com/MetaMask/contributor-docs) and [MetaMask Extension Coding Standards](https://github.com/MetaMask/metamask-extension/blob/main/.github/guidelines/CODING_GUIDELINES.md).
- [x] I've completed the PR template to the best of my ability
- [x] I’ve included tests if applicable
- [x] I’ve documented my code using [JSDoc](https://jsdoc.app/) format if applicable
- [x] I’ve applied the right labels on the PR (see [labeling guidelines](https://github.com/MetaMask/metamask-extension/blob/main/.github/guidelines/LABELING_GUIDELINES.md)). Not required for external contributors.

## **Pre-merge reviewer checklist**

- [x] I've manually tested the PR (e.g. pull and build branch, run the app, test code being changed).
- [x] 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.

app/scripts/migrations/135.test.ts

@@ -18,7 +18,7 @@ describe('migration #135', () => {
     expect(newStorage.meta).toStrictEqual({ version: 135 });
   });
 
-  it('should set stx opt-in to true and mark as migration-enabled when opt-in status is null', async () => {
+  it('should preserve existing state when opt-in status is null (default-enabled from previous versions)', async () => {
     const oldStorage: VersionedData = {
       meta: { version: prevVersion },
       data: {
@@ -34,11 +34,34 @@ describe('migration #135', () => {
     expect(
       newStorage.data.PreferencesController?.preferences
         ?.smartTransactionsOptInStatus,
-    ).toBe(true);
+    ).toBe(null);
     expect(
       newStorage.data.PreferencesController?.preferences
         ?.smartTransactionsMigrationApplied,
-    ).toBe(true);
+    ).toBe(false);
+  });
+
+  it('should preserve existing state when opt-in status is null (default-enabled from previous versions)', async () => {
+    const oldStorage: VersionedData = {
+      meta: { version: prevVersion },
+      data: {
+        PreferencesController: {
+          preferences: {
+            smartTransactionsOptInStatus: null,
+          },
+        },
+      },
+    };
+
+    const newStorage = await migrate(oldStorage);
+    expect(
+      newStorage.data.PreferencesController?.preferences
+        ?.smartTransactionsOptInStatus,
+    ).toBe(null);
+    expect(
+      newStorage.data.PreferencesController?.preferences
+        ?.smartTransactionsMigrationApplied,
+    ).toBe(false);
   });
 
   it('should set stx opt-in to true and mark as migration-enabled when opt-in status is undefined', async () => {

app/scripts/migrations/135.ts

@@ -43,7 +43,6 @@ function transformState(state: VersionedData['data']) {
 
   if (
     currentOptInStatus === undefined ||
-    currentOptInStatus === null ||
     (currentOptInStatus === false && !hasExistingSmartTransactions(state))
   ) {
     state.PreferencesController.preferences = {