The first full run under the strict runner surfaced 12 failures with one
root cause: injecting a single throwaway GSTACK_HOME per invocation made
6,900 tests share a MUTABLE scratch home. gstack-config tests wrote keys
into it; relink and update-check tests then read them (e.g. relink saw
skill_prefix left behind by a config test and produced prefixed names).
All 12 pass when run directly.
TMPDIR isolation stays (mkdtemp inside it is still per-call unique).
Tests needing GSTACK_HOME isolation mkdtemp their own per test — the
repo convention — and hermetic-env covers E2E children. The env-dump pin
now asserts GSTACK_HOME passes through UNTOUCHED so the injection can't
come back.
Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
