fix(core): limit v2 subagent nesting depth (#37291)

packages/core/src/config/experimental.ts

@@ -0,0 +1,10 @@
+export * as ConfigExperimental from "./experimental"
+
+import { Schema } from "effect"
+import { NonNegativeInt } from "../schema"
+
+export class Info extends Schema.Class<Info>("ConfigExperimental.Info")({
+  subagent_depth: NonNegativeInt.pipe(Schema.optional).annotate({
+    description: "Maximum subagent nesting depth. Defaults to 1.",
+  }),
+}) {}