diff --git a/web/src/model/create.test.ts b/web/src/model/create.test.ts
index 6e7cabe..4ead346 100644
--- a/web/src/model/create.test.ts
+++ b/web/src/model/create.test.ts
@@ -168,6 +168,12 @@ describe('catalog', () => {
     expect(resolveCreateCatalog([imageOnly], [definition], 'sample-image')?.template).toBe(imageOnly)
   })
 
+  test('marketplace definitions are never paired with a template, even when listed first with the same shape', () => {
+    const marketplace: ApplicationStackDefinition = { ...definition, id: 'builder-console', catalogSource: 'appthrust' }
+    expect(resolveCreateCatalog([template], [marketplace, definition], 'github-template')?.definitionRef?.name).toBe(definition.id)
+    expect(resolveCreateCatalog([template], [marketplace], 'github-template')).toBeUndefined()
+  })
+
   test('template allowlists trim and ignore case like the Platform validator; empty allowlists admit all templates', () => {
     const blocked = { ...sourceConnection, allowedRepositories: ['appthrust/template-other'] }
     expect(templateSourceProblem(template, [blocked])).toBe('not-admitted')
diff --git a/web/src/model/create.ts b/web/src/model/create.ts
index 22f6a2c..8241726 100644
--- a/web/src/model/create.ts
+++ b/web/src/model/create.ts
@@ -156,8 +156,11 @@ export function templatesFor(
 
 /**
  * Picks the requested (or default, or first) template for the source kind, and
- * the stack definition whose component count matches it. Templates do not
- * reference a definition, so the pairing is structural.
+ * the platform-shipped stack definition whose component count matches it.
+ * Templates do not reference a definition, so the pairing is structural;
+ * marketplace apps (`catalogSource` set, owned by an AppCatalogSource) are
+ * ApplicationStackDefinitions too and must never be candidates, or the template
+ * deploys that app's image under the user's name.
  */
 export function resolveCreateCatalog(
   templates: readonly ApplicationTemplateSummary[],
@@ -168,7 +171,7 @@ export function resolveCreateCatalog(
   const candidates = templatesFor(templates, sourceKind)
   const template = templateId ? candidates.find((item) => item.id === templateId) : candidates[0]
   if (!template) return undefined
-  const definition = definitions.find((item) => item.components.length === template.components.length)
+  const definition = definitions.find((item) => !item.catalogSource && item.components.length === template.components.length)
   if (!definition) return undefined
   const version =
     definition.versions?.find((item) => item.default && item.served !== false) ??