# Stable Explanation, Original Trace, and Counterfactuals

VacOptimizer exposes one client-side calculation context. Its immutable submitted snapshot and planning outcome are independent from three explanation concerns:

- the stable plan explanation is derived from the final displayed plan and remains useful for complete or incumbent plans;
- the calculation trace is captured while the producing run executes, grouped by phase and atomic decision, and may become ready after the outcome;
- counterfactual date analysis is an explicitly hypothetical operation that removes only the selected final placement, or starts from a selected trace decision's exact pre-decision state, and never rewrites the plan or historical trace.

The public planning outcome is delivered as soon as planning work finishes. Trace capture and delivery have separate readiness/failure state, remain local to the latest calculation, and cannot turn a valid outcome into an explanation error. Counterfactual work is cancellable or ignored when its calculation identity is stale. The existing deterministic constraint-first planner and its planning-work deadline remain unchanged.