Fix autoload_path_set_by_me_for? with inceptions

lib/zeitwerk/loader.rb

@@ -545,7 +545,7 @@ def all_dirs
       if autoload_path = cref.autoload?
         autoload_path if autoloads.key?(autoload_path)
       else
-        Registry.inception?(cref.path)
+        Registry.inception?(cref.path, self)
       end
     end
 

lib/zeitwerk/registry.rb

@@ -110,9 +110,12 @@ def register_inception(cpath, abspath, loader)
 
       # @private
       # @sig (String) -> String?
-      def inception?(cpath)
+      def inception?(cpath, registered_by_loader=nil)
         if pair = inceptions[cpath]
-          pair.first
+          abspath, loader = pair
+          if registered_by_loader.nil? || registered_by_loader.equal?(loader)
+            abspath
+          end
         end
       end
 

test/lib/zeitwerk/test_reloading.rb

@@ -96,6 +96,34 @@ def silence_exceptions_in_threads
     end
   end
 
+  test 'reloading namespaces that are inceptions in other projects' do
+    on_teardown do
+      remove_const :MyGem
+      delete_loaded_feature "lib/my_gem.rb"
+    end
+
+    gem_files = [["lib/my_gem.rb", <<~EOS]]
+      Zeitwerk::Loader.for_gem.setup
+      module MyGem; end
+    EOS
+
+    app_files = [["app/my_gem/foo.rb", 'MyGem::Foo = true']]
+
+    with_files(gem_files + app_files) do
+      with_load_path("lib") do
+        require 'my_gem'
+
+        loader.push_dir("app")
+        loader.enable_reloading
+        loader.setup
+
+        assert MyGem::Foo
+        loader.reload
+        assert MyGem::Foo
+      end
+    end
+  end
+
   test "reloading raises if the flag is not set" do
     e = assert_raises(Zeitwerk::ReloadingDisabledError) do
       loader = Zeitwerk::Loader.new