feat(account-tree-controller): always fire :selectedAccountGroupChange on init (#8427)

## Explanation

We used to not persist the `selectedAccountGroup` property before this
change:
- #8245

As a side-effect of this new persistence, we're not re-sending
`:selectedAccountGroupChange` on `init` and a lot of controllers were
relying on this behavior.

We re-introduce this behavior so every controllers can decide how to
handle that.

## References

N/A

## Checklist

- [ ] I've updated the test suite for new or updated code as appropriate
- [ ] I've updated documentation (JSDoc, Markdown, etc.) for new or
updated code as appropriate
- [ ] I've communicated my changes to consumers by [updating changelogs
for packages I've
changed](https://github.com/MetaMask/core/tree/main/docs/processes/updating-changelogs.md)
- [ ] I've introduced [breaking
changes](https://github.com/MetaMask/core/tree/main/docs/processes/breaking-changes.md)
in this PR and have prepared draft pull requests for clients and
consumer packages to resolve them

<!-- CURSOR_SUMMARY -->
---

> [!NOTE]
> **Medium Risk**
> Changes event-emission semantics so `selectedAccountGroupChange` now
fires on every `init`/`reinit`, which may trigger extra startup work or
duplicate handling in subscribers that assumed it only emitted on
changes.
> 
> **Overview**
> Ensures `AccountTreeController` *always* publishes
`AccountTreeController:selectedAccountGroupChange` at the end of `init`
(and therefore `reinit`), even when the selected group value is
unchanged.
> 
> Adds a regression test covering the reinit-with-same-accounts case and
updates the package changelog to document the restored behavior.
> 
> <sup>Reviewed by [Cursor Bugbot](https://cursor.com/bugbot) for commit
0689a7b. Bugbot is set up for automated
code reviews on this repo. Configure
[here](https://www.cursor.com/dashboard/bugbot).</sup>
<!-- /CURSOR_SUMMARY -->

Author: ccharly

packages/account-tree-controller/CHANGELOG.md

@@ -9,6 +9,8 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 ### Changed
 
+- Always fire `:selectedAccountGroupChange` during `init` call ([#8427](https://github.com/MetaMask/core/pull/8427))
+  - Many controllers were actually relying on this behavior when this used to be dynamic, so we re-introduce this behavior.
 - Now persist `accounTree` ([#8437](https://github.com/MetaMask/core/pull/8437))
   - The tree is not persisted and can be used before `init` is called.
   - This allow consumers (like the assets controllers) to rely on the selected group's accounts right away.

packages/account-tree-controller/src/AccountTreeController.test.ts

@@ -4586,6 +4586,48 @@ describe('AccountTreeController', () => {
       );
     });
 
+    it('always emits selectedAccountGroupChange on init even if the selected group did not change', () => {
+      const { controller, messenger, mocks } = setup({
+        accounts: [MOCK_HD_ACCOUNT_1],
+        keyrings: [MOCK_HD_KEYRING_1],
+      });
+
+      mocks.AccountsController.getSelectedMultichainAccount.mockImplementation(
+        () => MOCK_HD_ACCOUNT_1,
+      );
+
+      controller.init();
+
+      const defaultAccountGroupId = toMultichainAccountGroupId(
+        toMultichainAccountWalletId(MOCK_HD_ACCOUNT_1.options.entropy.id),
+        MOCK_HD_ACCOUNT_1.options.entropy.groupIndex,
+      );
+
+      expect(controller.state.selectedAccountGroup).toStrictEqual(
+        defaultAccountGroupId,
+      );
+
+      const selectedAccountGroupChangeListener = jest.fn();
+      messenger.subscribe(
+        'AccountTreeController:selectedAccountGroupChange',
+        selectedAccountGroupChangeListener,
+      );
+
+      // Re-init with the same accounts — the selected group still exists and has not changed.
+      controller.reinit();
+
+      expect(controller.state.selectedAccountGroup).toStrictEqual(
+        defaultAccountGroupId,
+      );
+      // The event must fire even though the group did not change, so that
+      // subscribers that missed the first init can still react accordingly.
+      expect(selectedAccountGroupChangeListener).toHaveBeenCalledWith(
+        defaultAccountGroupId,
+        defaultAccountGroupId,
+      );
+      expect(selectedAccountGroupChangeListener).toHaveBeenCalledTimes(1);
+    });
+
     it('emits selectedAccountGroupChange when setSelectedAccountGroup is called', () => {
       // Use different keyring types to ensure different groups
       const { controller, messenger } = setup({

packages/account-tree-controller/src/AccountTreeController.ts

@@ -418,18 +418,15 @@ export class AccountTreeController extends BaseController<
       }
     });
 
-    // We still compare the previous and new value, the previous one could have been
-    // an empty string and `#getDefaultSelectedAccountGroup` could also return an
-    // empty string too, thus, we would re-use the same value here again. In that
-    // case, no need to fire any event.
-    if (previousSelectedAccountGroup !== this.state.selectedAccountGroup) {
-      log(`Selected (initial) group is: [${this.state.selectedAccountGroup}]`);
-      this.messenger.publish(
-        `${controllerName}:selectedAccountGroupChange`,
-        this.state.selectedAccountGroup,
-        previousSelectedAccountGroup,
-      );
-    }
+    // We always fire the current selected group after init, even if it did not change, to ensure that
+    // all subscribers are aware of it and can react accordingly (e.g. by fetching accounts from
+    // the selected group on startup).
+    log(`Selected (initial) group is: [${this.state.selectedAccountGroup}]`);
+    this.messenger.publish(
+      `${controllerName}:selectedAccountGroupChange`,
+      this.state.selectedAccountGroup,
+      previousSelectedAccountGroup,
+    );
 
     log('Initialized!');
     this.#initialized = true;