Windows CreateProcess caps lpCommandLine at 32,767 chars. The original
`execFileSync(node, ['--test', ...546 paths])` exceeded that on every
Windows runner and exited within ~70ms with no test output. Linux/macOS
allow ~2 MB ARG_MAX so the same call worked there.
`scripts/run-tests.cjs` now splits selected files into chunks that keep
each spawn's argv under 28,000 chars (operator-overridable via
RUN_TESTS_MAX_CMDLINE_CHARS), runs them sequentially, and reports the
first non-zero exit. Cross-platform regression test forces chunking with
a low ceiling and asserts the `run-tests: chunk N/M …` stderr marker.
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
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