perf(ui): scope cooldown heartbeat to visible items

docs/plans/2026-07-25-modern-runtime-slice-h.md

@@ -45,7 +45,7 @@ and repeated stable provider polls allocate no report/wrap objects.
 Landed evidence:
 [`../research/2026-07-25-slice-h-a1-ui-text-cache.md`](../research/2026-07-25-slice-h-a1-ui-text-cache.md).
 
-### H-a2 — visible cooldown participants
+### H-a2 — visible cooldown participants — COMPLETE
 
 1. Keep the shared retail heartbeat and one cooldown result per represented
    item.
@@ -59,6 +59,9 @@ Gate: hidden inventory, equipment, external-container, vendor, and spell-bar
 lists are not scanned; reopening immediately displays the authoritative
 cooldown step.
 
+Landed evidence:
+[`../research/2026-07-25-slice-h-a2-cooldown-scope.md`](../research/2026-07-25-slice-h-a2-cooldown-scope.md).
+
 ### H-a3 — equipped-child transition work
 
 1. Preserve both frame ordering points: pre-network presentation and

docs/research/2026-07-25-slice-h-a2-cooldown-scope.md

@@ -0,0 +1,24 @@
+# Slice H-a2 — retained cooldown heartbeat scope
+
+Retail updates item cooldown children from
+`UIElement_UIItem::DoHeartbeat @ 0x004E1DF0`. Hidden retained subtrees do not
+receive that heartbeat.
+
+The shared acdream controller now keeps the same one-result-per-item heartbeat,
+but:
+
+- returns before reading the clock or visiting a slot when the authoritative
+  enchantment registry has no cooldown entries;
+- visits a mounted `UiItemList` only when the list and every ancestor are
+  visible;
+- clears the frame's step projection first, so a hidden-only item cannot retain
+  a stale ring;
+- recomputes the authoritative step on the first heartbeat after the panel
+  becomes visible;
+- retains existing future-slot and shared-cooldown-group behavior.
+
+Focused tests cover shared groups/future cells, hidden-parent suppression and
+reopen, and the zero-work empty-registry path.
+
+Release gate: 3,781 App tests passed / 3 skipped; 8,265 complete-solution
+tests passed / 5 skipped.