diff --git a/character-builder/backend/src/data/data.controller.ts b/character-builder/backend/src/data/data.controller.ts
index ef72505..2e265d5 100644
--- a/character-builder/backend/src/data/data.controller.ts
+++ b/character-builder/backend/src/data/data.controller.ts
@@ -35,7 +35,10 @@ const ALLOWED = new Set<string>([
 export class DataController {
   @Get(':file')
   @Header('Content-Type', 'application/json; charset=utf-8')
-  @Header('Cache-Control', 'public, max-age=3600')
+  // These files change with the data extractor and schema. A 3600s cache
+  // bit us once — a browser held an older shape after a schema migration
+  // and crashed the UI. Force revalidation per request.
+  @Header('Cache-Control', 'no-cache, must-revalidate')
   one(@Param('file') file: string, @Res() res: Response) {
     if (!ALLOWED.has(file)) {
       throw new BadRequestException('unknown data file');
diff --git a/character-builder/frontend/src/data.ts b/character-builder/frontend/src/data.ts
index 563868e..1c2959f 100644
--- a/character-builder/frontend/src/data.ts
+++ b/character-builder/frontend/src/data.ts
@@ -10,7 +10,11 @@ import type {
 const API = '/api/data';
 
 async function getJSON<T>(file: string): Promise<T> {
-  const res = await fetch(`${API}/${file}`);
+  // cache-bust against stale browser caches that hold an older schema for
+  // these files. The query string is ignored server-side but defeats any
+  // long-lived Cache-Control we (or a CDN) may have previously sent.
+  const url = `${API}/${file}?v=2`;
+  const res = await fetch(url, { cache: 'no-cache' });
   if (!res.ok) throw new Error(`fetch ${file}: ${res.status}`);
   return res.json() as Promise<T>;
 }
@@ -49,5 +53,23 @@ export async function loadFaction(house: House): Promise<FactionTable> {
 }
 
 export async function loadSkillTree(id: ClassId): Promise<SkillTree> {
-  return getJSON<SkillTree>(`skills-${id}.json`);
+  const raw = await getJSON<any>(`skills-${id}.json`);
+  // Backwards-compat: an older snapshot of this file had {nodes, edges} at
+  // the top level instead of {subtrees}. Treat it as a single anonymous
+  // subtree so the UI doesn't blow up on iteration.
+  if (raw && !raw.subtrees && Array.isArray(raw.nodes)) {
+    return {
+      id: raw.id,
+      name: raw.name,
+      subtrees: [
+        {
+          name: '',
+          cols: Math.max(1, ...raw.nodes.map((n: any) => n.col || 1)),
+          nodes: raw.nodes,
+          edges: raw.edges || [],
+        },
+      ],
+    } as SkillTree;
+  }
+  return raw as SkillTree;
 }