Codex App: conversation history lost on branch switch

When working on a branch and then switching to another (e.g. during a PR review/merge flow), all conversations from the original branch disappear.

Repro: Work on a feature branch → ask AI to PR-review and merge into staging/main → conversations from the feature branch are gone (including the one you were just in).

Expected: Conversations persist across branch switches.
Actual: Conversations are lost and unrecoverable after switching branches.