Fix bogus store-not-found error on store switch when ___from_store is absent

[TuVanDev]

Description (*)

Magento\Store\Controller\Store\SwitchAction::execute() resolves the origin store from the ___from_store request param, falling back to the store cookie:

$fromStoreCode = $this->_request->getParam(
    '___from_store',
    $this->storeCookieManager->getStoreCodeFromCookie()
);
...
$fromStore = $this->storeRepository->get($fromStoreCode);

When neither ___from_store nor a store cookie is present, $fromStoreCode is null, so StoreRepository::get(null) throws NoSuchEntityException. The controller catches it and shows the misleading error:

The store that was requested wasn't found. Verify the store and try again.

…even though the target store (___store) is perfectly valid. The message appears as a flash message and disappears on the next request, which makes it look intermittent and leaves no log entry.

A concrete real-world trigger is the admin CMS → Pages → Select → View ("View Page") preview of a page assigned to the default store view. Core's Magento\Cms\ViewModel\Page\Grid\UrlBuilder::prepareRequestQuery() deliberately omits ___from_store when the target equals the default store view, so a staff member previewing such a page (with no store cookie yet) always hits this error.

This PR falls back to the current store as the origin store when none is provided. A store-to-itself switch then simply sets the cookie and redirects with no error, and a genuine cross-store switch with a missing ___from_store gets the correct origin. Genuinely invalid target stores still raise the error as before.

Related Pull Requests

None.

Fixed Issues (if relevant)

N/A — reproducible on 2.4-develop (see manual testing below).

Manual testing scenarios (*)

1. Ensure the browser has no store cookie (fresh/incognito session).
2. Visit https://<base-url>/stores/store/switch/?___store=default (a valid store code, no ___from_store).
   • Before: you are redirected back, and the page shows the error "The store that was requested wasn't found. Verify the store and try again."
   • After: you are redirected back with no error message.
3. Alternatively, in Admin go to Content → Pages, and for a page assigned to the default store view click Select → View.
   • Before: the storefront page shows the error banner.
   • After: no error banner.
4. Regression — a real cross-store switch (?___from_store=default&___store=<other>) and a genuinely invalid target (?___store=does_not_exist) behave exactly as before (valid switch works; invalid target still errors).

Integration coverage added in SwitchActionTest::testSwitchWithoutFromStoreDoesNotError().

Questions or comments

The current store is used as the origin store because ___from_store semantically means "the store the visitor is switching from", i.e. the current request context. $this->storeManager is already used a few lines below in the same method.

Contribution checklist (*)

• Pull request has a meaningful description of its purpose
• All commits are accompanied by meaningful commit messages
• All new or changed code is covered with unit/integration tests (added integration test)
• All automated tests passed successfully (all affected tests pass)

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