Fail closed on low-disk pnpm recovery

[xiaojiou176]

Summary

• fail closed before workspace-local ENOSPC recovery when host disk headroom is already below the minimum threshold
• clean up active workspace retry stores on install-script failure so dashboard/desktop closeout does not leave multi-GB residue behind
• register the new headroom knobs and sync the root/docs wording

Verification

• bash -n scripts/install_dashboard_deps.sh && bash -n scripts/install_desktop_deps.sh
• python3 -m pytest apps/orchestrator/tests/test_runtime_log_path_guardrails.py
• npm run scan:host-process-risks
• CORTEXPILOT_HYGIENE_SKIP_UPSTREAM=1 bash scripts/check_repo_hygiene.sh
• npm run truth:triage (repo-side truth passes; only external ui-audit-playwright remains)
• pre-commit run --all-files

Review

• l2-reviewer blocker-only verdict: APPROVE / no blocker