experiment: narrow acknowledge behaviour eligibility

lib/behaviour-selection/behaviour-selector.js

@@ -30,10 +30,29 @@ const PRIORITIES = {
   continue: 5, // default
 };
 
+/* ── Acknowledge exclusion gate ─────────────────────────────── */
+
+/**
+ * Deterministic exclusions for Acknowledge.
+ * Returns true when Acknowledge should not fire, even if its positive trigger matches.
+ * This gate qualifies the trigger; it does not replace it.
+ */
+function isAcknowledgeExcluded(assessment) {
+  // Phase-based exclusions: synthesising and concluding states call for Summarise, not Acknowledge
+  if (["synthesising", "concluding"].includes(assessment.phase.value)) return true;
+  // Progress-based exclusion: stalled progress calls for Pause, not Acknowledge
+  if (assessment.progress.value === "stalled") return true;
+  // Health-based exclusion: user_overloaded calls for Pause, not Acknowledge
+  if (assessment.conversationHealth.value === "user_overloaded") return true;
+  return false;
+}
+
 /* ── Selection rules (one rule per behaviour) ─────────────── */
 
 function selectAcknowledge(assessment) {
   if (assessment.conversationHealth.value === "healthy" && assessment.phase.confidence !== "low") {
+    // Apply exclusion gate before returning acknowledge
+    if (isAcknowledgeExcluded(assessment)) return null;
     return {
       behaviour: "acknowledge",
       confidence: "medium",