diff --git a/cypress/platform/viewer.js b/cypress/platform/viewer.js
index da3d2e0da82..0847ad66805 100644
--- a/cypress/platform/viewer.js
+++ b/cypress/platform/viewer.js
@@ -42,7 +42,7 @@ const contentLoaded = async function () {
     pos = pos + 7;
     const graphBase64 = document.location.href.substr(pos);
     const graphObj = JSON.parse(b64ToUtf8(graphBase64));
-    if (graphObj.mermaid && graphObj.mermaid.theme === 'dark') {
+    if (graphObj.mermaid?.theme === 'dark') {
       document.body.style.background = '#3f3f3f';
     }
     console.log(graphObj);
diff --git a/packages/mermaid/src/diagrams/git/gitGraphAst.ts b/packages/mermaid/src/diagrams/git/gitGraphAst.ts
index 0dbc1ecb03b..82cf3b0a2de 100644
--- a/packages/mermaid/src/diagrams/git/gitGraphAst.ts
+++ b/packages/mermaid/src/diagrams/git/gitGraphAst.ts
@@ -425,7 +425,7 @@ function prettyPrintCommitHistory(commitArr: Commit[]) {
     }
   }
   log.debug(label.join(' '));
-  if (commit.parents && commit.parents.length == 2 && commit.parents[0] && commit.parents[1]) {
+  if (commit.parents?.length == 2 && commit.parents?.[0] && commit.parents?.[1]) {
     const newCommit = state.records.commits.get(commit.parents[0]);
     upsert(commitArr, commit, newCommit);
     if (commit.parents[1]) {
diff --git a/packages/mermaid/src/diagrams/sequence/sequenceDb.ts b/packages/mermaid/src/diagrams/sequence/sequenceDb.ts
index 3d79b9ea616..049d131d49d 100644
--- a/packages/mermaid/src/diagrams/sequence/sequenceDb.ts
+++ b/packages/mermaid/src/diagrams/sequence/sequenceDb.ts
@@ -192,7 +192,7 @@ export class SequenceDB implements DiagramDB {
       old.box = assignedBox;
 
       // Don't allow description nulling
-      if (old && name === old.name && description == null) {
+      if (old?.name === name && description == null) {
         return;
       }
     }
diff --git a/packages/mermaid/src/docs/.vitepress/homepageHeroCopy.ts b/packages/mermaid/src/docs/.vitepress/homepageHeroCopy.ts
index 6f8f79d2019..5e3c96b1981 100644
--- a/packages/mermaid/src/docs/.vitepress/homepageHeroCopy.ts
+++ b/packages/mermaid/src/docs/.vitepress/homepageHeroCopy.ts
@@ -10,7 +10,7 @@ const LOG_PREFIX = '[MMD_DOCS_HERO]';
  * Note: index.md frontmatter is static, so this is applied via VitePress transformPageData.
  */
 export function applyHomePageHeroCopy(pageData: any, hostname: string): void {
-  if (!pageData || pageData.relativePath !== 'index.md') {
+  if (pageData?.relativePath !== 'index.md') {
     return;
   }
 
diff --git a/packages/mermaid/src/docs/.vitepress/theme/mermaid.ts b/packages/mermaid/src/docs/.vitepress/theme/mermaid.ts
index 4b44f20b46f..0190991c766 100644
--- a/packages/mermaid/src/docs/.vitepress/theme/mermaid.ts
+++ b/packages/mermaid/src/docs/.vitepress/theme/mermaid.ts
@@ -4,9 +4,9 @@ import tidyTreeLayout from '../../../../../mermaid-layout-tidy-tree/dist/mermaid
 import layouts from '../../../../../mermaid-layout-elk/dist/mermaid-layout-elk.core.mjs';
 
 const init = Promise.all([
-  mermaid.registerExternalDiagrams([zenuml]),
-  mermaid.registerLayoutLoaders(layouts),
-  mermaid.registerLayoutLoaders(tidyTreeLayout),
+  Promise.resolve(mermaid.registerExternalDiagrams([zenuml])),
+  Promise.resolve(mermaid.registerLayoutLoaders(layouts)),
+  Promise.resolve(mermaid.registerLayoutLoaders(tidyTreeLayout)),
 ]);
 mermaid.registerIconPacks([
   {
diff --git a/packages/mermaid/src/rendering-util/layout-algorithms/dagre/index.js b/packages/mermaid/src/rendering-util/layout-algorithms/dagre/index.js
index e9f0266e263..ea798c0b15a 100644
--- a/packages/mermaid/src/rendering-util/layout-algorithms/dagre/index.js
+++ b/packages/mermaid/src/rendering-util/layout-algorithms/dagre/index.js
@@ -164,6 +164,15 @@ const recursiveRender = async (_elem, graph, diagramType, id, parentCluster, sit
 
   dagreLayout(graph);
 
+  // Strip out any virtual ordering edges that were injected for edge-less
+  // clusters (see mermaid-graphlib.js). They must be removed before rendering
+  // so that no SVG edge path is drawn for them.
+  graph.edges().forEach(function (e) {
+    if (graph.edge(e)?._virtual) {
+      graph.removeEdge(e.v, e.w, e.name);
+    }
+  });
+
   log.info('Graph after layout:', JSON.stringify(graphlibJson.write(graph)));
   // Move the nodes to the correct place
   let diff = 0;
diff --git a/packages/mermaid/src/rendering-util/layout-algorithms/dagre/mermaid-graphlib.js b/packages/mermaid/src/rendering-util/layout-algorithms/dagre/mermaid-graphlib.js
index f0e5cd5ed9b..8281d5bc2f8 100644
--- a/packages/mermaid/src/rendering-util/layout-algorithms/dagre/mermaid-graphlib.js
+++ b/packages/mermaid/src/rendering-util/layout-algorithms/dagre/mermaid-graphlib.js
@@ -274,12 +274,16 @@ export const adjustClustersAndEdges = (graph, depth) => {
       graph.removeEdge(e.v, e.w, e.name);
       if (v !== e.v) {
         const parent = graph.parent(v);
-        clusterDb.get(parent).externalConnections = true;
+        if (parent && clusterDb.has(parent)) {
+          clusterDb.get(parent).externalConnections = true;
+        }
         edge.fromCluster = e.v;
       }
       if (w !== e.w) {
         const parent = graph.parent(w);
-        clusterDb.get(parent).externalConnections = true;
+        if (parent && clusterDb.has(parent)) {
+          clusterDb.get(parent).externalConnections = true;
+        }
         edge.toCluster = e.w;
       }
       log.warn('Fix Replacing with XXX', v, w, e.name);
@@ -359,11 +363,35 @@ export const extractor = (graph, depth) => {
 
       log.warn('Old graph before copy', graphlibJson.write(graph));
       copy(node, graph, clusterGraph, node);
+
+      // When a subgraph cluster that has an explicitly declared direction
+      // contains no edges, Dagre places all nodes in a single rank and lays
+      // them out along the cross-axis of that rankdir (e.g. `direction LR`
+      // produces a vertical column). To honour the user's declared direction
+      // we inject temporary, layout-only ordering edges (A → B → C → D …) that
+      // force Dagre to distribute the nodes across separate ranks. The edges
+      // are marked with `_virtual: true` so they can be stripped out in the
+      // rendering phase before any SVG paths are drawn.
+      const clusterMeta = clusterDb.get(node);
+      if (clusterMeta?.clusterData?.dir && clusterGraph.edges().length === 0) {
+        const clusterNodes = clusterGraph.nodes();
+        log.warn('Cluster has no edges, adding virtual ordering edges for layout', clusterNodes);
+        for (let i = 0; i < clusterNodes.length - 1; i++) {
+          clusterGraph.setEdge(clusterNodes[i], clusterNodes[i + 1], {
+            _virtual: true,
+            weight: 0,
+            minlen: 1,
+          });
+        }
+      }
+
+      const existingNodeData = graph.node(node) || {};
       graph.setNode(node, {
+        ...existingNodeData,
         clusterNode: true,
         id: node,
-        clusterData: clusterDb.get(node).clusterData,
         label: clusterDb.get(node).label,
+        clusterData: clusterDb.get(node).clusterData,
         graph: clusterGraph,
       });
       log.warn('New graph after copy node: (', node, ')', graphlibJson.write(clusterGraph));
diff --git a/packages/mermaid/src/rendering-util/layout-algorithms/dagre/mermaid-graphlib.spec.js b/packages/mermaid/src/rendering-util/layout-algorithms/dagre/mermaid-graphlib.spec.js
index 11acd44eb18..c2a498a34f3 100644
--- a/packages/mermaid/src/rendering-util/layout-algorithms/dagre/mermaid-graphlib.spec.js
+++ b/packages/mermaid/src/rendering-util/layout-algorithms/dagre/mermaid-graphlib.spec.js
@@ -400,6 +400,88 @@ flowchart TB
     expect(aGraph.parent('B')).toBe(undefined);
   });
 });
+
+describe('Virtual ordering edges for edge-less clusters', () => {
+  let g;
+  beforeEach(function () {
+    setLogLevel(1);
+    g = new graphlib.Graph({
+      multigraph: true,
+      compound: true,
+    });
+    g.setDefaultEdgeLabel(function () {
+      return {};
+    });
+  });
+
+  // Build a graph where cluster Y has no external edges (so it gets extracted
+  // into a clusterNode) and no internal edges (so virtual ordering edges are injected).
+  // The outer node X has no edge to Y; only Y's children are present.
+  const makeEdgelessCluster = (rankdir) => {
+    g.setGraph({
+      rankdir,
+      nodesep: 50,
+      ranksep: 50,
+      marginx: 8,
+      marginy: 8,
+    });
+    g.setNode('A', { data: 1 });
+    g.setNode('B', { data: 2 });
+    g.setNode('C', { data: 3 });
+    g.setNode('D', { data: 4 });
+    g.setNode('Y', { data: 5, dir: rankdir });
+    g.setParent('A', 'Y');
+    g.setParent('B', 'Y');
+    g.setParent('C', 'Y');
+    g.setParent('D', 'Y');
+    // NO edges to/from Y — ensures externalConnections stays false
+    // so Y gets extracted as a clusterNode
+  };
+
+  for (const dir of ['TB', 'BT', 'LR', 'RL']) {
+    it(`should inject virtual ordering edges for an edge-less cluster with direction ${dir}`, () => {
+      makeEdgelessCluster(dir);
+      adjustClustersAndEdges(g);
+
+      const yClusterNode = g.node('Y');
+      expect(yClusterNode).toBeDefined();
+      expect(yClusterNode.clusterNode).toBe(true);
+
+      const yGraph = yClusterNode.graph;
+      expect(yGraph.nodes().length).toBe(4);
+
+      // There should be exactly 3 virtual ordering edges (A→B, B→C, C→D)
+      const edges = yGraph.edges();
+      expect(edges.length).toBe(3);
+      edges.forEach((e) => {
+        expect(yGraph.edge(e)._virtual).toBe(true);
+      });
+    });
+  }
+
+  it('should NOT inject virtual edges when the cluster already has internal edges', () => {
+    g.setGraph({ rankdir: 'LR', nodesep: 50, ranksep: 50, marginx: 8, marginy: 8 });
+    g.setNode('A', { data: 1 });
+    g.setNode('B', { data: 2 });
+    g.setNode('Y', { data: 3, dir: 'LR' });
+    g.setParent('A', 'Y');
+    g.setParent('B', 'Y');
+    // One real internal edge — should prevent virtual edge injection
+    g.setEdge('A', 'B', { data: 'real' });
+
+    adjustClustersAndEdges(g);
+
+    const yClusterNode = g.node('Y');
+    expect(yClusterNode?.clusterNode).toBe(true);
+
+    const yGraph = yClusterNode.graph;
+    const edges = yGraph.edges();
+    expect(edges.length).toBe(1);
+    expect(yGraph.edge(edges[0]).data).toBe('real');
+    // No _virtual marker on the real edge
+    expect(yGraph.edge(edges[0])._virtual).toBeUndefined();
+  });
+});
 describe('extractDescendants', function () {
   let g;
   beforeEach(function () {
diff --git a/vite.config.ts b/vite.config.ts
index f86711e9ab2..b73b0cfe25a 100644
--- a/vite.config.ts
+++ b/vite.config.ts
@@ -15,6 +15,7 @@ export default defineConfig({
   test: {
     environment: 'jsdom',
     globals: true,
+    testTimeout: 30000,
     // TODO: should we move this to a mermaid-core package?
     coverage: {
       provider: 'v8',