In the asset controller, throw if tenancy isn't initialized

Instead of falling back to returning storage_path('app/public') in assetRoot(), throw an exception *at the start of the method* -- tenant assets shouldn't be served in central context.

tests/TenantAssetTest.php

@@ -17,6 +17,7 @@ use Stancl\Tenancy\Middleware\InitializeTenancyByRequestData;
 use Stancl\Tenancy\Bootstrappers\FilesystemTenancyBootstrapper;
 use Stancl\Tenancy\Bootstrappers\UrlGeneratorBootstrapper;
 use Stancl\Tenancy\Controllers\TenantAssetController;
+use Stancl\Tenancy\Enums\RouteMode;
 use Stancl\Tenancy\Events\TenancyEnded;
 use Stancl\Tenancy\Listeners\RevertToCentralContext;
 use Stancl\Tenancy\Overrides\TenancyUrlGenerator;
@@ -180,6 +181,23 @@ test('tenant asset controller throws when the configured disk is not local or no
     }
 });
 
+test('tenant assets cannot be served in central context', function () {
+    config([
+        'tenancy.identification.default_middleware' => InitializeTenancyByRequestData::class,
+        // Make the asset route skip tenant identification
+        'tenancy.default_route_mode' => RouteMode::UNIVERSAL,
+    ]);
+
+    $this->withoutExceptionHandling();
+
+    foreach ([null, 'local'] as $publicDisk) {
+        TenantAssetController::$publicDisk = $publicDisk;
+
+        expect(fn () => pest()->get(tenant_asset('foo.txt')))
+            ->toThrow(Exception::class, 'Tenant assets can only be served in tenant context.');
+    }
+});
+
 test('tenant assets are served from the resolved root of the configured disk', function () {
     config([
         'tenancy.identification.default_middleware' => InitializeTenancyByRequestData::class,