docs: close experiment 42 selector refinement

docs/current-project-state.md

@@ -75,7 +75,7 @@ The following were built during Experiments 18–25B. They are isolated diagnost
 
 ## 6. Work Currently Paused
 
-- Engine experiments are at Experiment 40 (behaviour reachability diagnostic — no rule changes).
+- Engine experiments advanced through Experiment 42 (narrow Acknowledge exclusion gate for behaviour selection; production selector changed but Behaviour Selection remains isolated with no runtime caller).
 - UI experiments are paused;
 - Knowledge-management experiments are complete (confirmed by Experiment 38 cold-start validation);
 - Nothing historical has been deleted or archived yet.
@@ -100,7 +100,7 @@ Historical documents are retained under `docs/archive/` and should be opened onl
 
 ## 8. Return-to-Work Summary
 
-Engine experiments advanced to Experiment 41, which compared two passive alternatives for reducing Acknowledge dominance. Variant B (Acknowledge exclusions via phase/progress/health gates) is recommended over Variant A (priority reordering with false-positive side effects). Both variants converge on the same two genuine changes: `concluding → summarise` and `stalled → pause`. No production code changed.
+Engine experiments advanced through Experiment 42, which implemented Variant B's narrow Acknowledge exclusion gate in the production selector. Summarise now appears at conclusion; Pause now appears when stalled. Behaviour Selection remains passive and isolated with no runtime caller — active user-facing engine behaviour did not change. Clarify remains unresolved. No active tests rerun as part of documentation closure.
 
 First document to read: `docs/current-project-state.md`. Then consult `.claude/architecture-guardrails.md` before any code changes and `docs/project-knowledge-inventory.md` for task-specific references. The full experiment history remains available in `docs/design-evolution-log.md` but is no longer default reading.