In this example, Ruby fails an assertion and crashes. I think we should either provide support for this, or we should explicitly provide a syntax error indicating that ** isn't allowed in constant writes when ractor pragmas are enabled.
For kwsplat, it just calls compile_hash (which generates hash_merge_kw call after the hash generation), generates a freeze call on the compiled hash and then calls ensure_shareable on that hash if shareable_constant_value is literal.