Adds a "session runtime resolved" audit event that flows through the engine's main execution lanes — triage, executor, reviewer, merger, heartbeat, step-session-executor, and mission-execution-loop — with runtime mutation support and test coverage, plus a compile-fix for the merger auditor wiring. Fusion-Task-Id: FN-5544 Co-authored-by: Fusion (runfusion.ai) <noreply@runfusion.ai> Fusion-Task-Id: FN-5544