Mechanism: Git for Windows on arm64 ships native git.exe but an x86-64 MSYS
usr/bin/bash.exe, which runs under the WoA x64 emulator. With the os-tests
lane's 16 parallel workers, a replayed step's bash dies before running a line
with 0xC000026F (STATUS_WX86_INTERNAL_ERROR) or 0xC0000005 and empty
stdout/stderr, so an unmodified baseline replay fails as a bare
AssertionError (jobs 112635777217 and 112764629268, two different nodeids).
Repro (throwaway workflows on the real runners, previous commit's diagnostics):
- windows-latest-32-arm-core, 16 copies of the file's replay tests at once,
4 rounds: 21/64 copies red, every failure 0xC000026F.
- Same load, windows-latest-32-core (x64): 0/64.
- Passing SYSTEMROOT/WINDIR or the full Windows env to the step: 12/48 and
17/48 vs 15/48 base, so the stripped env is not the cause.
- One process, 32 threads, 600 replays: 0 crashes; it takes concurrent
processes, i.e. host-wide emulator load.
Seam: _NATIVE_WINDOWS_TOO keeps platforms("linux", "windows") and adds a
skipif for win32 + native_arch() == arm64. The x64 Windows row still runs the
replay on the Windows layout (python.exe-only venv, Git Bash), Linux arm64
keeps it (native bash), and the routing guard that pins the marker passes.
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