Show HN: I checked 10 AI-written patches to real C++ projects – 6 didn't hold up

Unfix is an independent verifier for C/C++ and firmware bug fixes that reproduces the bug on the base version, applies the fix with sanitizers on, checks other tests still pass, then reverts the fix to confirm the bug returns, returning VERIFIED, REJECTED or NOT VERIFIABLE without an LLM in the verdict. In a public benchmark of 10 AI-generated patches (from Codex CLI) against real bugs in fmt, spdlog, zlib-ng and cpp-peglib, judged against maintainers' hidden reference tests, Unfix verified 4 and rejected 6. It runs as an MCP tool in agents like Claude Code and Codex, as a GitHub PR check (demo repository only), in the terminal, and on STM32 NUCLEO boards via ST-Link.