Reuse validation costs when fitting and batching

docs/roadmap/remediation.md

@@ -601,6 +601,8 @@ immutable render inputs are shared safely across sections of the same stage.
 
 ## R17 — P3: Reuse Validation Payload Costs While Fitting and Batching
 
+**Status:** Completed. The built-in estimator composes compact JSON costs across context fitting and greedy batching. Other estimators retain exact serialization. Equivalence tests cover trimmed context, oversized items, token counts, batch splits, escaped text, and local references.
+
 **Category**
 
 Quadratic prefix serialization in the existing budgeting path now used with