PHP silently transforming all string keys of a map to integers when they are all integer strings ("123", "456" etc.) is exactly one of the reasons I'll never choose a language that pulls the rug from below my feet and replaces it with parquet.

If you bother to read the manual [1], it explicitly states that this happens. Almost at the top of the page. Hardly "silent".

[1] https://www.php.net/manual/en/language.types.array.php

It's not reasonable to expect such gotchas. It might have been a 20px red bold text on top of php.net and it would still be very not okay.

No.