Refactor: Enforce type safety, fix close deadlock, implement assignee restrictions and notify admin fallbacks

app/Models/Department.php

@@ -15,6 +15,11 @@ class Department extends Model
         return $this->belongsTo(User::class, 'manager_id');
     }
 
+    public function members(): HasMany
+    {
+        return $this->hasMany(User::class);
+    }
+
     public function feedbacks(): HasMany
     {
         return $this->hasMany(Feedback::class, 'current_department_id');