Dual sessions branching from a single session after another session sends a message to it

What version of the Codex App are you using (From “About Codex” dialog)?

26.715.31925

What subscription do you have?

max

What platform is your computer?

Darwin 25.5.0 arm64 arm

What issue are you seeing?

SessionA: 019f793c-0bfb-7221-adb4-c72c5d59f66c
was running, and another sessionB: 019f7b8c-8323-7533-ade2-5d03bdf35c77
Interrupts it with a message.

SessionA had compacted, and the pre-compaction session received the message and started to go on its own
while the post-compacted session kept on going.

The codex UI looked like it had 2 sessions going simulatenously split by the Context automatically compacted message.

<img width="400" height="131" alt="Image" src="https://github.com/user-attachments/assets/cec34c58-4835-4b4e-bd2d-89437911d2b3" />

What steps can reproduce the bug?

Not sure, I think it happened because the message was sent while the compaction was happening but cannot verify.

What is the expected behavior?

No split

Additional information

_No response_