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Linux built the 3 configs sequentially (~3x a single config); Windows already parallelizes. Run them concurrently via ThreadPoolExecutor, splitting make -j across configs to avoid CPU oversubscription. Symlink setup serialized with a lock. --no-parallel restores sequential. Brings Linux wall time close to Windows. Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>