Resolved 5 separate GitHub Actions errors that had been latent since
v1.0.67 and were blocking the CI badge:

1. --skip-extraction now warns instead of failing (5 E2E jobs)
2. Windows MSVC cross-compile (G29) target stdlib now installs
3. Miri step now disables mimalloc via cfg flag
4. Windows reaper dead-code warnings now cfg-gated (2 jobs)
5. (previously in v1.0.73) cross container + upload-artifact v6

10/10 local validation gates PASS. Zero src/ semantic changes for the
reaper and Miri fixes; --skip-extraction reverted to its v1.0.45
behavior.