* fix(codex): keep parent turns active during sub-agent work
Codex multi-agent activity is thread-scoped. Treating child events as root
activity could end the foreground turn early and splice child output into
parent messages.
Route legacy and current activity shapes through stable child identities and
preserve message boundaries across live and resumed turns.
* fix(codex): preserve sub-agent details across stream chunks
Keep empty activity paths explicit and normalize the synthetic assistant
boundary for every chunk in the active message.
* fix(codex): route legacy child events by thread
* fix(codex): stabilize sub-agent activity lifecycles
* fix(codex): retain child tool activity and terminal state
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