Two leaks from the test temp plumbing:
tests/conftest.py relocates pytest's basetemp out of the native Hermes
home (#111101) with mkdtemp(dir=native.parent), which is the operator's
$HOME, and nothing removed it: 123 hermes-pytest-basetemp-* dirs (552 MB)
appeared there in a day, one per bare pytest process. The relocated
basetemp now goes into one prunable root (/var/tmp/hermes-pytest on
POSIX, a non-dotted sibling of the native home elsewhere), is removed at
pytest_unconfigure, and idle siblings from killed runs are swept on entry.
scripts/run_tests_parallel.py deletes each per-file temp root in finally,
but a SIGKILLed runner (tool timeout, stray pkill) never gets there and
leaks one root per in-flight worker: 983 r-* roots (3.4 GB) in three
days. The runner now sweeps 24h-idle roots at start and forces read-only
permission fixtures writable before rmtree instead of skipping them.
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