test(adapter-sessions): stabilize cleanup race coverage

[avksp]

Summary

• cancel immediately after the persisted RUNNING state and retain strict first-cancel assertions
• coordinate same-byte artifact replacement strictly between the two real artifact collections
• remove timing-dependent daemon writes and module-global time mocking

Validation

• focused changed tests: 50 repeats on Python 3.12 and 50 on Python 3.14
• full suite: 2039 tests PASS on Python 3.14
• Python quality evidence and validation: PASS
• repository hygiene: PASS
• neutrality tracked-release: zero findings
• Grok 4.6 xhigh independent review: PASS after one remediation round
• OpenCode GLM 5.3 strict read-only independent review: PASS

This patch changes tests only. It does not alter cleanup, cancellation, timeout, artifact, security, architecture, or quality policy behavior.