Coordinated child session replies no longer reach the coordinator chat after latest update #5444

After the most recent app update (2026-11-12, morning), replies from coordinated child sessions no longer come back to the coordinating chat.

Setup: a general chat coordinates child project sessions created with create_session (autopilot, notify_on_idle).

Observed:

• The child finishes work, but the coordinator only receives an "idle after processing a turn" notification. get_session returns only metadata, with no final response.
• Messages sent to a child via send_session_message are accepted for priority delivery, but the reply (cross_session_message) often does not arrive for a long time, or the coordinator must ask again.
• Before the update, the child's final report arrived reliably after it went idle.

Expected: the child's final report is delivered to the coordinator when the child goes idle, or a tool exists to read the child's last response.

Environment: GitHub Copilot app, version 1.0.106-8, Windows.