AppleClang ships llvm-cov inside Xcode and it is not on PATH, so find_program fails. Use xcrun llvm-cov gcov via a wrapper script instead.
Add Coverage.cmake with gcovr integration, detecting Clang vs GCC and wrapping llvm-cov gcov in a build-dir script to handle paths with spaces on Windows. Update README and AGENTS.md with the new one-command-per-block documentation rule.
portersky