refactor(planning): remove the original decision trace

docs/adr/0004-separate-plan-explanation-from-calculation-trace.md

@@ -1,5 +1,7 @@
-# Separate Plan Explanations from Calculation Traces
+# Stable Plan Explanations Without Decision History
 
-The automatic planning deadline referenced below is superseded by [ADR 0006](0006-user-selected-horizons-and-cancellable-calculations.md), implemented by issue #59. Technical callers can still opt into an explicit planning-work budget; the user flow has no automatic cutoff.
+Issue #76 supersedes this ADR's original requirement to capture and deliver a complete calculation trace. The original decision trace, historical analysis, replay and candidate-history retention are removed end to end.
 
-VacOptimizer provides a stable plan explanation separately from the complete, untruncated calculation trace captured during the same planning run; on-demand counterfactual date analysis is identified as hypothetical and never presented as trace history. Explanation and tracing must not alter the planning outcome, so trace instrumentation is excluded from the planner deadline and the result may appear before the latest run's in-memory trace finishes loading; this narrows ADR 0003's ten-second hard limit to planning work rather than end-to-end trace delivery. This accepts additional transient memory and wall-clock time instead of inventing scalar day scores, truncating history, or reconstructing a trace by replay.
+The stable explanation describes the displayed plan, including valid incomplete incumbents: entitlement and rule provenance, contributions, the full ordered objective comparison and first decisive objective, time-off periods, remaining balances and concrete non-placement reasons. Invalid input and obligation conflicts retain their distinct explanations.
+
+Outcomes are delivered before explanation work. Explanation failures cannot discard an available outcome. Immutable calculation, valid-incumbent and final-state snapshots remain available for cancellation recovery and hypothetical analysis; they are independent of tracing. ADR 0006's opt-in technical planning-work budget excludes observer callbacks and post-outcome explanation work. The user flow has no automatic elapsed-time cutoff.