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

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

@@ -175,6 +175,9 @@ export const Info = Schema.Struct({
       primary_tools: Schema.optional(Schema.mutable(Schema.Array(Schema.String))).annotate({
         description: "Tools that should only be available to primary agents.",
       }),
+      subagent_depth: Schema.optional(NonNegativeInt).annotate({
+        description: "Maximum subagent nesting depth. Defaults to 1.",
+      }),
       continue_loop_on_deny: Schema.optional(Schema.Boolean).annotate({
         description: "Continue the agent loop when a tool call is denied",
       }),

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

@@ -77,6 +77,10 @@ export function migrate(info: typeof ConfigV1.Info.Type) {
     commands: commands(info.command),
     instructions: info.instructions,
     references: info.references ?? info.reference,
+    experimental:
+      info.experimental?.subagent_depth === undefined
+        ? undefined
+        : { subagent_depth: info.experimental.subagent_depth },
     plugins: info.plugin?.map((plugin) =>
       typeof plugin === "string" ? plugin : { package: plugin[0], options: plugin[1] },
     ),