The unit tier runs under xdist, so another worker's push could start an ssh-agent between a test's count and its check. The test sshd now tags every session with NISSE_TEST_SSHD=<its root>, and the tests count only agents carrying their own sshd's tag. A new test starts a foreign agent alongside and checks it isn't counted. Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com> Claude-Session: https://claude.ai/code/session_01J5Utyfzw7gF7UhjRDEtjTk