Proposed resolution:

This wording is relative to N5050.

1. Modify [version.syn] as indicated:

   #define __cpp_lib_format             202603L // also in <format>
   #define __cpp_lib_format_error_code  202606L // also in <system_error>
   #define __cpp_lib_format_path        202506L // also in <filesystem>
   

P3395R6 added a `std::formatter` specialization for `error_code`, but without a feature test macro. During the review of the pull request to apply the paper to the working draft there were requests for a feature test macro.