Skip Object.const_get entirely to prevent autoloader deadlocks

const_defined? returns true for constants registered via
Module#autoload (as Zeitwerk does), so guarding const_get with
const_defined? still triggers autoloading and deadlocks.

Instead, skip string-to-class resolution entirely:
- Registry.find_by_class: only walk ancestors when name is already
  a Class object; return nil for strings. Use Registry.add_alias to
  register subclasses that should inherit a parent's throttle.
- Throttled.requeue_throttled: pass the class name string directly
  to Registry.get instead of resolving it with const_get.

Fixes #213

Made-with: Cursor

Author: NeelamAggarwal

lib/sidekiq/throttled.rb

@@ -96,19 +96,12 @@ def throttled?(message)
       # Return throttled job to be executed later, delegating the details of how to do that
       # to the Strategy for that job.
       #
-      # Uses +const_defined?+ before +const_get+ to avoid triggering
-      # autoloading (e.g. Zeitwerk) from Sidekiq's fetcher thread, which
-      # runs outside the Rails reloader and can deadlock or raise.
-      #
       # @return [void]
       def requeue_throttled(work)
         message = JSON.parse(work.job)
         class_name = message.fetch("wrapped") { message.fetch("class") { return false } }
-        return false unless Object.const_defined?(class_name)
-
-        job_class = Object.const_get(class_name)
 
-        Registry.get job_class do |strategy|
+        Registry.get class_name do |strategy|
           strategy.requeue_throttled(work)
         end
       end

lib/sidekiq/throttled/registry.rb

@@ -99,22 +99,22 @@ def find(name)
 
         # Find strategy by class or it's parents.
         #
-        # Uses +const_defined?+ before +const_get+ to avoid triggering
-        # autoloading (e.g. Zeitwerk) from Sidekiq's fetcher thread, which
-        # runs outside the Rails reloader and can deadlock or raise.
+        # Only performs ancestor lookup when +name+ is already a Class.
+        # String-based lookup via +Object.const_get+ is intentionally
+        # skipped because it triggers autoloading (e.g. Zeitwerk) from
+        # Sidekiq's fetcher thread, which runs outside the Rails reloader
+        # and can deadlock or raise. Use +Registry.add_alias+ to register
+        # subclasses that should inherit a parent's throttle strategy.
         #
         # @param name [Class, #to_s]
         # @return [Strategy, nil]
         def find_by_class(name)
-          const = name.is_a?(Class) ? name : (Object.const_get(name) if Object.const_defined?(name))
-          return unless const.is_a?(Class)
+          return unless name.is_a?(Class)
 
-          const.ancestors.each do |m|
+          name.ancestors.each do |m|
             strategy = find(m.name)
             return strategy if strategy
           end
-        rescue NameError
-          nil
         end
       end
     end