fix(delegate-task): reject stray backend-style categories

Ultraworked with [Sisyphus](https://github.com/code-yeongyu/oh-my-openagent)

Co-authored-by: Sisyphus <clio-agent@sisyphuslabs.ai>

src/tools/delegate-task/category-resolver.ts

@@ -45,12 +45,26 @@ export async function resolveCategoryExecution(
 ): Promise<CategoryResolutionResult> {
   const { client, userCategories, sisyphusJuniorModel } = executorCtx
 
-  const availableModels = await getAvailableModelsForDelegateTask(client)
-
   const categoryName = args.category!
   const enabledCategories = mergeCategories(userCategories)
   const categoryExists = enabledCategories[categoryName] !== undefined
 
+  if (!categoryExists) {
+    const allCategoryNames = Object.keys(enabledCategories).join(", ")
+    return {
+      agentToUse: "",
+      categoryModel: undefined,
+      categoryPromptAppend: undefined,
+      maxPromptTokens: undefined,
+      modelInfo: undefined,
+      actualModel: undefined,
+      isUnstableAgent: false,
+      error: `Unknown category: "${categoryName}". Available: ${allCategoryNames}`,
+    }
+  }
+
+  const availableModels = await getAvailableModelsForDelegateTask(client)
+
   const resolved = resolveCategoryConfig(categoryName, {
     userCategories,
     inheritedModel,