+/**
+ * @brief Find the last fence-related backtracking conflict for a ModelAction
+ *
+ * This function performs the search for the most recent conflicting action
+ * against which we should perform backtracking, as affected by fence
+ * operations. This includes pairs of potentially-synchronizing actions which
+ * occur due to fence-acquire or fence-release, and hence should be explored in
+ * the opposite execution order.
+ *
+ * @param act The current action
+ * @return The most recent action which conflicts with act due to fences
+ */