119 build config target reaches backend

// Pins that `std/build:config { "target": ... }` ACTUALLY cross-compiles, not
// merely that the block parses.
//
// The two existing build:config tests (310_057, 310_058) are COMPILE_ONLY and
// assert only that the annotation survives quote-escaping. Nothing in the corpus
// read the architecture of the produced binary — so when target threading
// stopped working, no marker moved:
//
//   2026-02-13  blog "A 14KB Docker Image That Serves HTTP" ships a real
//               x86_64-linux-musl binary cross-compiled from macOS.
//   2026-05-04  tests/.../embedded_blinky/results.md records the koru row as
//               `native`, "no cross-compile threading for that toolchain yet".
//   2026-06-01  koru-os/FINDINGS.md reproduces it in 9 lines and calls it a
//               toolchain gap.
//
// The gap was not real — those probes wrote `std.build:config` with the retired
// dot namespace. But the corpus could not tell the difference between "cross
// -compiles" and "silently builds native", and that is what this test closes.
//
// No `[build(...)]` annotation, so the config always matches (build.kz:57) and
// no CLI flag is needed. The assertion is a comptime one INSIDE a fired tor: an
// unfired `pub tor main` emits a main() holding only the flow prologue and
// epilogue, so its body would never be analysed and the wall would not exist.
//
// COMPILE_ONLY because the artifact is an x86_64 Linux binary that cannot run on
// a macOS/arm64 host. Compiling IS the assertion.

const std = @import("std");

~std/build:config {
    "target": "x86_64-linux-musl"
}

~pub tor assert-target { }

~proc assert-target|zig {
    const builtin = @import("builtin");
    if (builtin.cpu.arch != .x86_64)
        @compileError("std/build:config target did not reach the backend: emitted code compiled for " ++ @tagName(builtin.cpu.arch) ++ ", expected x86_64");
    if (builtin.os.tag != .linux)
        @compileError("std/build:config target did not reach the backend: emitted code compiled for " ++ @tagName(builtin.os.tag) ++ ", expected linux");
    std.debug.print("target reached the backend\n", .{});
}

const fire = true;

~if(fire)
| then |> assert-target()
| else |> _