feat: guard Deployer singleton before Host construction

src/Deployer.php

@@ -66,7 +66,7 @@
  */
 class Deployer extends Container
 {
-    private static Deployer $instance;
+    private static ?self $instance = null;
 
     public function __construct(Application $console)
     {
@@ -167,9 +167,26 @@ public function __construct(Application $console)
 
     public static function get(): self
     {
+        if (self::$instance === null) {
+            throw new \RuntimeException('Deployer is not initialized.');
+        }
+
         return self::$instance;
     }
 
+    public static function hasInstance(): bool
+    {
+        return self::$instance !== null;
+    }
+
+    /**
+     * @internal For tests that need a clean Deployer singleton between cases.
+     */
+    public static function resetInstance(): void
+    {
+        self::$instance = null;
+    }
+
     public function init(): void
     {
         $this->addTaskCommands();

src/Host/Host.php

@@ -29,7 +29,7 @@ class Host
     public function __construct(string $hostname)
     {
         $parent = null;
-        if (Deployer::get()) {
+        if (Deployer::hasInstance()) {
             $parent = Deployer::get()->config;
         }
         $this->config = new Configuration($parent);

tests/src/Host/HostTest.php

@@ -8,10 +8,16 @@
 namespace Deployer\Host;
 
 use Deployer\Configuration;
+use Deployer\Deployer;
 use PHPUnit\Framework\TestCase;
 
 class HostTest extends TestCase
 {
+    protected function tearDown(): void
+    {
+        Deployer::resetInstance();
+    }
+
     public function testHost()
     {
         $host = new Host('host');