The free runner treats this isolation as MANDATORY (two concurrent shards
on one Chromium profile kill each other's browser; shared tmp
cross-contaminates) — the paid lane had none of it. Doubly load-bearing
here: a shard that hits its 30-min wall is group-SIGKILLed, so per-test
afterAll cleanup never runs; the rmSync backstop is the only thing keeping
wedged runs from accumulating full git-repo workspaces in the shared
tmpdir forever. This is the DAG prerequisite for raising EVALS_JOBS (next
commit) — more concurrency on shared state amplifies exactly the
shared-tree race class opus-47 exhibited.
Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
