fix: use invisible ordering edges to enforce DO_TRY section order

Layer constraints (FIRST/LAST) don't work for disconnected components
in ELK's layered algorithm. Replace with invisible edges that chain
try_body → doFinally → doCatch to guarantee correct top-to-bottom order.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

cameleer3-server-app/src/main/java/com/cameleer3/server/app/diagram/ElkDiagramRenderer.java

@@ -356,6 +356,12 @@ public class ElkDiagramRenderer implements DiagramRenderer {
             allEdges.addAll(collectAllEdges(hr));
         }
         for (ElkEdge elkEdge : allEdges) {
+            // Skip invisible ordering edges used only for DO_TRY section layout
+            String edgeId = elkEdge.getIdentifier();
+            if (edgeId != null && edgeId.startsWith("__ordering_")) {
+                continue;
+            }
+
             String sourceId = elkEdge.getSources().isEmpty() ? "" : elkEdge.getSources().get(0).getIdentifier();
             String targetId = elkEdge.getTargets().isEmpty() ? "" : elkEdge.getTargets().get(0).getIdentifier();
 
@@ -568,6 +574,7 @@ public class ElkDiagramRenderer implements DiagramRenderer {
             }
 
             // Virtual _TRY_BODY wrapper with LR direction for horizontal try body chain
+            // Layer constraint FIRST ensures it stays at the top of the DO_TRY
             if (!tryBodyChildren.isEmpty()) {
                 String wrapperId = rn.getId() + "._try_body";
                 ElkNode wrapper = factory.createElkNode();
@@ -591,8 +598,7 @@ public class ElkDiagramRenderer implements DiagramRenderer {
                 }
             }
 
-            // Handler children stacked below try body: DO_FINALLY first, then DO_CATCH
-            // (ELK TB layout places children in insertion order)
+            // Handler children: DO_FINALLY in the middle, DO_CATCH at the bottom
             for (RouteNode child : handlerChildren) {
                 if (child.getType() == NodeType.DO_FINALLY) {
                     childNodeIds.add(child.getId());
@@ -607,6 +613,30 @@ public class ElkDiagramRenderer implements DiagramRenderer {
                             compoundNodeIds, childNodeIds, doTryNodeIds);
                 }
             }
+
+            // Create invisible ordering edges to enforce top-to-bottom:
+            // try_body → doFinally → doCatch
+            List<ElkNode> orderedSections = new ArrayList<>();
+            if (!tryBodyChildren.isEmpty()) {
+                orderedSections.add(elkNodeMap.get(rn.getId() + "._try_body"));
+            }
+            for (RouteNode child : handlerChildren) {
+                if (child.getType() == NodeType.DO_FINALLY) {
+                    orderedSections.add(elkNodeMap.get(child.getId()));
+                }
+            }
+            for (RouteNode child : handlerChildren) {
+                if (child.getType() == NodeType.DO_CATCH) {
+                    orderedSections.add(elkNodeMap.get(child.getId()));
+                }
+            }
+            for (int i = 0; i < orderedSections.size() - 1; i++) {
+                ElkEdge orderEdge = factory.createElkEdge();
+                orderEdge.setIdentifier("__ordering_" + rn.getId() + "_" + i);
+                orderEdge.setContainingNode(elkNode);
+                orderEdge.getSources().add(orderedSections.get(i));
+                orderEdge.getTargets().add(orderedSections.get(i + 1));
+            }
         } else if (isCompound) {
             compoundNodeIds.add(rn.getId());
             elkNode.setWidth(200);