feat(subagent): catalog one-shot child sessions

packages/subagent/tool-subagent/src/index.ts

@@ -280,6 +280,7 @@ export function apply(ctx: Context, config: Config): void {
 
         const maxDepth = typeof config.maxDepth === 'number' ? config.maxDepth : undefined
         const request = {
+          label: args.description,
           prompt: [{ type: 'text', text: args.prompt }] as ContentBlock[],
           parent,
           ...config.agentOptions !== undefined ? { agentOptions: config.agentOptions } : {},

packages/subagent/tool-subagent/tests/scripted-provider.spec.ts

@@ -12,6 +12,7 @@ function fakeParent(id = 'parent-1'): Agent {
 
 function baseRequest(over: Partial<SubagentStartRequest> = {}): SubagentStartRequest {
   return {
+    label: 'task',
     prompt: [{ type: 'text', text: 'task' }],
     parent: fakeParent(),
     signal: new AbortController().signal,

packages/subagent/tool-subagent/tests/tool-subagent.spec.ts

@@ -1007,6 +1007,7 @@ describe('depth budget configuration', () => {
   it('defaults maxDepth to 3 and forwards it in the start request', async () => {
     const { ctx, requests } = await captureSetup()
     await callSubagent(ctx, { description: 'd', prompt: 'p' })
+    expect(requests[0]?.label).toBe('d')
     expect(requests[0]?.maxDepth).toBe(3)
     expect(requests[0]?.toolFilter).toBeUndefined()
   })