feat(web): rewrite subagent conversations for FIFO activation

packages/subagent/subagent/src/child-agent.ts

@@ -88,6 +88,8 @@ export function childSessionMeta(
   return {
     ...parentHeader.cwd !== undefined ? { cwd: parentHeader.cwd } : {},
     parentSession: parentHeader.id,
+    // Navigation classification only; the descriptor remains the authority
+    // for mode and continuation capability.
     origin: 'subagent',
     // Durable: the recursion budget must survive persistence and resume.
     delegationDepth: childDepth,

packages/subagent/subagent/tests/continuation.spec.ts

@@ -211,6 +211,7 @@ describe('SubagentService.startContinuable', () => {
     expect('surfaceOp' in descriptor).toBe(false)
     expect(loaded.meta.id).toBe(started.childId)
     expect(loaded.meta.parentSession).toBe(SessionId('parent'))
+    expect(loaded.meta.origin).toBe('subagent')
   })
 
   it('rolls the child back completely when the caller signal aborts before acceptance', async () => {