feat: allow sessions_spawn cross-agent

src/config/types.ts

@@ -717,6 +717,10 @@ export type RoutingConfig = {
       workspace?: string;
       agentDir?: string;
       model?: string;
+      subagents?: {
+        /** Allow spawning sub-agents under other agent ids. Use "*" to allow any. */
+        allowAgents?: string[];
+      };
       sandbox?: {
         mode?: "off" | "non-main" | "all";
         /** Agent workspace access inside the sandbox. */

src/config/zod-schema.ts

@@ -638,6 +638,11 @@ const RoutingSchema = z
             workspace: z.string().optional(),
             agentDir: z.string().optional(),
             model: z.string().optional(),
+            subagents: z
+              .object({
+                allowAgents: z.array(z.string()).optional(),
+              })
+              .optional(),
             sandbox: z
               .object({
                 mode: z