That's not what I'm criticizing. Lexical shadowing is not what I'm advocating. I think your choice is fine in so far as it goes. It has its logic.

What I am criticizing is how it can fail. The top scope is different, quantitatively and qualitatively, from almost all nested scopes. It's much larger, and spread lexically over a larger area. If you have a team of developers, it will be modified concurrently. No one developer necessarily knows the full set of symbols defined in the top scope while they are writing an individual procedure.

And thus the problem: a developer thinks they've chosen a "different (better) name" for a some variable, but in fact they've chosen one that a different developer also thought was a "different (better) name", only one of them is in a lexically enclosing scope. This problem isn't likely to occur on the level of nested procedures or nested blocks, because the definitions would be visually close. But it's much more likely to happen when one of the symbols is defined in the top scope. Here, the definition could be many hundreds or thousands of lines away. It may even be in a separate commit, waiting to be merged, such that there's no way for either developer to know without closely reviewing every change.

And this is the criticism: the failure mode for this inadvertent reuse of a variable name is subtle bugs, as what one developer thought was a global symbol turns out to be modified and acquire strange values through unexpected codeflow, almost like the VM was corrupted and memory was behaving unreliably.

The qualitative difference of the top scope in situations like this is the reason why I suggested sigils or somesuch to disambiguate those scenarios. Perhaps top-level symbols can't be reassigned from nested scopes unless you use '$' as a prefix to their name; a visual shorthand that you are definitely not creating a new local symbol.

The reason I summarized your argument in the way I did is because your argument against this failure mode seems to be "don't create top scopes with lots of symbols". That's a fine argument (or rather, exhortation), but it isn't a realistic one. If the language is problematic with lots of symbols in the top scope, it should be unpleasant to use with lots of symbols in the top scope. And the unpleasantness shouldn't come from subtle bugs (the passive aggressiveness I mentioned); it should come from awkward and ugly sigils, or some other intrinsic way of discouraging those styles.