zu-c holds the idiom item

[tamnd]

zu-c's practice score goes from 50 to 67. The item is idiom, at 15, the largest single item on any card here: "The language's own shapes: how it iterates, how it releases a resource, how it awaits, what it raises. A binding that reads like the C ABI in another syntax is a binding nobody wants to write against."

67 rather than 75 because zu-c is scored out of 90: it owes no api-map, since the C names are zu.h and zu.h is generated in the engine, and no perf report.

	before	after
zu-c practice	50	67
missing	reference, idiom, install, stability	reference, install, stability

The work is tamnd/zu-c#9. Three parts.

A dropped return was a lost failure. Ninety of the calls in zu.hpp answer something a caller must not drop, and three of them said so. A try_ call answers a std::expected whose error half is the failure report, so conn.try_query(q); on a line of its own compiles, throws nothing, returns nothing and loses the reason. All ninety are [[nodiscard]] now, and it caught a real one in the existing suite on the first build.

The bug it found. zu.hpp read __cpp_lib_expected before <version> had defined it. An undefined identifier is nought in a preprocessor arithmetic expression, so ZU_HAS_EXPECTED came out 0 on GCC 13 at -std=c++23, where std::expected has been available since GCC 12, and the whole try_ half of the API went undeclared on a toolchain that has it. Worse than absent, it depended on include order: a translation unit that had already included <version> got a different zu.hpp than one that had not, in the same build.

Nothing said so, because test_expected.cpp is one #if with a single placeholder case in the #else for the C++20 floor. ctest ran the placeholder, printed Passed, and eleven cases about the half a caller who builds without exceptions depends on had not been compiled by anything. That branch now carries an #error: below C++23 there is nothing to run, but at C++23 and above this half missing is a broken build rather than a quiet one.

Printing. <format> was included at the top of the header and ZU_HAS_FORMAT defined beside it, and neither was used in the header, the tests, the examples or the README. There is now a to_string for every type worth printing and a std::formatter over each, one line apiece, so the C++20 floor gets the same text as C++23. No operator<<, because <ostream> would land in every translation unit that includes the header whether it prints or not.

test_idiom.cpp pins the shapes with concepts rather than prose: Result is a sized, common, random access range of Row and deliberately not a borrowed_range, so filtering a temporary result is a compile error where it was written rather than a use after free that works in a debug build; handles move and do not copy; exceptions descend from std::runtime_error; the value structs are std::regular.

The overview below was regenerated by cargo xtask clients, which still reports "7 clients, 5 of them tier 1, 4 at their tier's practice threshold". zu-c is not one of the four and should not be until its card is finished.