diff --git a/src/config/schema.ts b/src/config/schema.ts
index cea3300c..5f684b57 100644
--- a/src/config/schema.ts
+++ b/src/config/schema.ts
@@ -161,6 +161,8 @@ export const CategoryConfigSchema = z.object({
   textVerbosity: z.enum(["low", "medium", "high"]).optional(),
   tools: z.record(z.string(), z.boolean()).optional(),
   prompt_append: z.string().optional(),
+  /** Mark agent as unstable - forces background mode for monitoring. Auto-enabled for gemini models. */
+  is_unstable_agent: z.boolean().optional(),
 })
 
 export const BuiltinCategoryNameSchema = z.enum([