fix: use documented directadmin binary

exec/lib/DirectAdminVacationApi.php

@@ -5,14 +5,19 @@ class DirectAdminVacationApi
 {
     /** @var callable|null */
     private $request;
-    private string $daBinary = '/usr/local/bin/da';
+    private string $daBinary = '/usr/local/directadmin/directadmin';
 
-    public function __construct(string $daBinary = '/usr/local/bin/da', ?callable $request = null)
+    public function __construct(string $daBinary = '/usr/local/directadmin/directadmin', ?callable $request = null)
     {
         $this->daBinary = $daBinary;
         $this->request = $request;
     }
 
+    public function directAdminBinary(): string
+    {
+        return $this->daBinary;
+    }
+
     /** @param array<string,mixed> $rule @return array<string,string> */
     public function buildSavePayload(string $email, array $rule, bool $exists = true): array
     {
@@ -133,7 +138,7 @@ class DirectAdminVacationApi
 
     private function apiUrl(string $owner): string
     {
-        $output = $this->run([$this->daBinary, 'api-url', '--user=' . $owner], '');
+        $output = $this->run([$this->resolveDirectAdminBinary(), 'api-url', '--user=' . $owner], '');
         $url = trim($output);
         if ($url === '' || !preg_match('#^https?://#', $url)) {
             throw new RuntimeException('Cannot determine DirectAdmin API URL for user');
@@ -141,9 +146,27 @@ class DirectAdminVacationApi
         return $url;
     }
 
+    private function resolveDirectAdminBinary(): string
+    {
+        $candidates = array_values(array_unique([
+            $this->daBinary,
+            '/usr/local/directadmin/directadmin',
+            '/usr/bin/da',
+        ]));
+        foreach ($candidates as $candidate) {
+            if ($candidate !== '' && is_executable($candidate)) {
+                return $candidate;
+            }
+        }
+        throw new RuntimeException('DirectAdmin binary is not executable. Checked: ' . implode(', ', $candidates));
+    }
+
     /** @param string[] $args */
     private function run(array $args, string $stdin): string
     {
+        if (($args[0] ?? '') !== '' && str_contains($args[0], '/') && !is_executable($args[0])) {
+            throw new RuntimeException('DirectAdmin API command is not executable: ' . $args[0]);
+        }
         $process = proc_open($args, [['pipe', 'r'], ['pipe', 'w'], ['pipe', 'w']], $pipes);
         if (!is_resource($process)) {
             throw new RuntimeException('Cannot start DirectAdmin API command');