The Linux unit-test shards set HOME to a fresh per-run directory for
isolation. scripts/tests/corepack-warmup.js (vitest globalSetup) spawns
`corepack pnpm --version` before any worker forks, and on a cold HOME
corepack downloads the pinned pnpm from registry.npmjs.org. The ECS
egress intermittently times out on that fetch (ETIMEDOUT to 104.16.9.34),
which kills the shard after every test file has already passed — today
that produced 7 PR-facing failures across random shard numbers (2/8,
5/8, 3/8, etc.), all on the same self-hosted host.
Install dependencies runs before the test step and warms the corepack
cache under the runner's real HOME, but the test step's HOME override
makes that cache invisible. Pin COREPACK_HOME to a per-run path in both
steps so they share the same cache without touching the HOME isolation.
Per-run, not persistent: corepack does not re-verify extracted entries
on cache hit, so a shared cache would be a poisoning channel (the same
reason lint_and_static keeps its COREPACK_HOME per-run).
Co-authored-by: Qwen-Coder <[email protected]>
