The problem was that after rebasing, the `useRebase` hook wasn't invalidating the `taskAttempt` query, so the Create PR dialog would read stale `target_branch` data from the cache. I added the missing invalidation at `frontend/src/hooks/useRebase.ts:43-46`, matching the pattern already used correctly in `useChangeTargetBranch.ts`.
Now when a user rebases via the UI, the task attempt query will be invalidated and the Create PR dialog will show the updated target/base branch.