[Bug] test_unittests_v2[unittest/_torch/executor] wrapper fails intermittently (~40%) with all inner tests passing — session teardown crash

Summary

test_unittests_v2[unittest/_torch/executor] fails intermittently in pre-merge single-GPU stages with AssertionError: failure reported in unittests while all ~953 inner executor tests report PASSED in the merged results.

Mechanics (from the wrapper stack): the parallel phase exits non-zero after tests complete, the --lf retry re-runs and passes everything, but the session still exits non-zero — i.e. a crash/failure in session teardown (thread-leak check or native crash at shutdown), not a test failure.

Occurrences (all on unrelated PR #15730, current-main bases)

• L0_MergeRequest_PR 47040 — B300-PyTorch-2
• L0_MergeRequest_PR 47191 — DGX_H100-PyTorch-3
• L0_MergeRequest_PR 47357 — B300-PyTorch-2
• L0_MergeRequest_PR 47366 — B300-PyTorch-2

That is 4 of ~10 runs — the single most frequent pre-merge blocker we hit while babysitting that PR. The NCCL shutdown fix (#15892) did not eliminate it.

Ask

Deflake the executor unittest group teardown (e.g. identify the leaking/crashing shutdown path, or apply the pytest.mark.threadleak(enabled=False) pattern used elsewhere if it is the threadleak gate).

Start by reproducing test_unittests_v2[unittest/_torch/executor] across repeated single-GPU runs and inspect the parallel phase, --lf retry, and session teardown. Investigate the executor group’s thread-leak check or native shutdown path, comparing the pytest.mark.threadleak(enabled=False) pattern used elsewhere. Done means the wrapper exits successfully without intermittent teardown failures while the inner tests still pass.