fix(core): limit subagent nesting depth (#37124)

Co-authored-by: Dax <mail@thdxr.com>

packages/core/src/v1/config/config.ts

@@ -81,6 +81,9 @@ export const Info = Schema.Struct({
     description:
       "Default agent to use when none is specified. Must be a primary agent. Falls back to 'build' if not set or if the specified agent is invalid.",
   }),
+  subagent_depth: Schema.optional(NonNegativeInt).annotate({
+    description: "Maximum subagent nesting depth. Defaults to 1, which prevents subagents from launching subagents.",
+  }),
   username: Schema.optional(Schema.String).annotate({
     description: "Custom username to display in conversations instead of system username",
   }),