test(subagent): close descendant listing coverage

packages/subagent/subagent/src/list-children.ts

@@ -315,8 +315,9 @@ function descendantCandidates(
     .reverse()
   const visited = new Set<SessionId>([rootSessionId])
   while (stack.length > 0) {
-    const position = stack.pop()
-    if (position === undefined) break
+    // The length guard proves one frame exists.
+    // oxlint-disable-next-line typescript/no-non-null-assertion
+    const position = stack.pop()!
     const id = position.record.header.id
     if (visited.has(id)) continue
     visited.add(id)

packages/subagent/subagent/tests/list-children.spec.ts

@@ -1009,6 +1009,52 @@ describe('SubagentService.listDescendants', () => {
     ])
   })
 
+  it('returns an empty result when the root has no descendants', async () => {
+    const { ctx, parent } = await setup([])
+    await ctx.sessions.flush(parent.session)
+    await expect(ctx.subagents.listDescendants(parent.id)).resolves.toEqual([])
+  })
+
+  it('omits a live creation-window candidate while continuing through its subtree', async () => {
+    const { ctx, parent } = await setup([])
+    const bareId = SessionId('live-creation-window')
+    const bare = ctx.sessions.create(bareId, {
+      meta: { createdAt: 1, parentSession: parent.id, origin: 'subagent' },
+    })
+    bare.append('turn/start', { turn: 1 })
+    const below = await authorChild(ctx, '00000000-0000-4000-8000-00000000aaaf', {
+      parentSession: bareId,
+      createdAt: 2,
+      origin: 'subagent',
+    }, childEvents(descriptorPayload('below the creation window')))
+
+    await expect(ctx.subagents.listDescendants(parent.id)).resolves.toEqual([{
+      kind: 'child', id: below, label: 'below the creation window', mode: 'continuable',
+      activity: 'inactive', hasChildren: false, parentId: bareId, depth: 2,
+    }])
+  })
+
+  it('contains a corrupt parent cycle without revisiting the requested root', async () => {
+    const { ctx } = await setup([])
+    const rootId = SessionId('cycle-root')
+    const nodeId = SessionId('cycle-node')
+    await authorChild(ctx, rootId, {
+      parentSession: nodeId,
+      createdAt: 2,
+    }, childEvents(descriptorPayload('ordinary cycle root')))
+    await authorChild(ctx, nodeId, {
+      parentSession: rootId,
+      createdAt: 1,
+      origin: 'subagent',
+    }, childEvents(descriptorPayload('cycle child')))
+
+    await expect(ctx.subagents.listDescendants(rootId)).resolves.toEqual([{
+      kind: 'child', id: nodeId, label: 'cycle child', mode: 'continuable',
+      activity: 'inactive', hasChildren: false, parentId: rootId, depth: 1,
+    }])
+  })
+
+
   it('walks a deeply nested ordinary-session chain without consuming the call stack', async () => {
     const { ctx, parent } = await setup([])
     const depth = 10_000