Compacting resurfaces completed tasks

What version of Codex is running?

codex-cli 0.64.0

What subscription do you have?

Plus

Which model were you using?

gpt-5.1-codex-max

What platform is your computer?

Darwin 25.0.0 arm64 arm

What issue are you seeing?

Compacting in the plan tool resurrected steps that were already marked completed. After compacting, “completed” tasks reappeared, effectively rolling the plan state backward (same symptom as GitHub issue #6077).

What steps can reproduce the bug?

Uploaded thread: 019ae3ed-0119-72d2-afea-9e39a2100ccd

What is the expected behavior?

Once a step is marked completed, compacting should not reintroduce it. The plan should remain stable with completed steps staying completed/hidden as appropriate, not resurfacing after compacting.

Additional information

_No response_