os.exec* is emulated on Windows (spawn + terminate the caller) and crashed
the release-windows build: it died with "Segmentation fault ... exit code
139" immediately after the wrapper printed the SDK fingerprint, before cargo
produced any output. The POSIX Linux and macOS builds using the same wrapper
were unaffected, which localised it to the Windows exec emulation.
Spawn cargo with subprocess.run and propagate its exit code. Portable across
all three targets; cargo output still streams through the inherited stdio and
CXXFLAGS/QMAKE plumbing is unchanged. Verified locally: the wrapper reaches
cargo and returns its status.
cc
vicrodh