[ruby-core:121981] [Ruby Bug#21317] Namespaces leak with object IDs

Issue #21317 has been updated by Eregon (Benoit Daloze).


Full reproducer, showing that even though `Object` is the same reference in all namespaces it can have different constants in different namespaces, but only if calling `constants` in that namespace:
```
$ RUBY_NAMESPACE=1 ruby -ve 'ns = Namespace.new; File.write "ns.rb", "O = Object; OC = Object.constants"; ns.require "./ns"; p Object.equal?(ns::O); p Object.constants == ns::OC; p Object.constants == ns::Object.constants'
ruby 3.5.0dev (2025-05-10T07:50:29Z namespace-on-read-.. bd4f57f96b) +PRISM [x86_64-linux]
ruby: warning: Namespace is experimental, and the behavior may change in the future!
See doc/namespace.md for know issues, etc.
true
false
true
```

I think this is expected behavior for Namespace so not sure it's worth reopening.

It does mean that with Namespace even though two objects (specifically core classes and modules) might be equal they are actually different when looked at in different namespaces.

----------------------------------------
Bug #21317: Namespaces leak with object IDs
https://bugs.ruby-lang.org/issues/21317#change-113098

* Author: fxn (Xavier Noria)
* Status: Closed
* Backport: 3.2: UNKNOWN, 3.3: UNKNOWN, 3.4: UNKNOWN
----------------------------------------
Namespaces are not transparent for this program

```ruby
if mod1.object_id == mod2.object_id
  mod1.constants == mod2.constants
end
```

because it may fail for `mod1 = Object; mod2 = ns::Object`, which have the same object ID.



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