[Bug]: Root and direct subagent appear completed while a nested subagent is still running #16902

Before submitting

• I searched existing issues and did not find a duplicate.
• I included enough detail to reproduce or investigate the problem.

Area

apps/web

Steps to reproduce

This describes a user-observed workflow. A fresh, isolated reproduction has not been run.

1. In a root thread, have the agent delegate work to subagent A.
2. Have A delegate further work to subagent B.
3. Let the root and A finish their own responses while B continues working.
4. Look at the activity/status shown from the original root thread.

Observed tree:

Root thread: completed
`-- Subagent A: completed
    `-- Subagent B: still running

Expected behavior

From the root thread, it should remain clear that delegated work is still active anywhere in its descendant tree, including beneath a child whose own response has finished. The same should hold at each ancestor level.

An agent's own response can be complete while its descendants remain active. The activity display should make that distinction and let the user find the running descendant. The outstanding-work indicator should clear only after the last descendant completes, fails, or is cancelled.

Actual behavior

The root thread and its direct subagent A are shown as completed while A's subagent B is still running. From the original thread, the user cannot see that this descendant is continuing to work. The displayed completion therefore makes the delegated workflow appear finished too early.

This report concerns visibility of ongoing nested work. It does not establish that execution stops or that results are lost, and no underlying cause has been confirmed.

Impact

Minor bug or occasional failure

The user cannot tell from the original thread whether the full delegated workflow has finished, or monitor the descendant that remains active.

Version or commit

Not established for the observed incident.

Environment

Nested subagent workflow in T3 Code. Exact client, provider, and model details have not been established for this incident.

Logs or stack traces

No logs or independent reproduction are attached; the report is based on the user's observation.

Workaround

No verified workaround.

Related reports and documented workflow

• #16603 reports a delegated task completing while its child has a running shell command. This report concerns a running grandchild agent and visibility from its ancestors.
• Discussion #15171 requests an optional Agents panel with descendant grouping. This report does not prescribe a new panel; it concerns the existing activity display appearing complete while nested work continues.
• The documented delegation workflow describes waiting for nested work and distinguishes a finished turn waiting for children from an available result. The exact delegation mechanism used in the observed incident has not been confirmed.