Preserve draft branch/worktree when update options are undefined

- Keep existing `branch` and `worktreePath` values when `setProjectDraftThreadId` receives `undefined`
- Add a regression test covering the undefined-update case
005e13089aJulius Marminge committed on 3/2/2026, 6:36:35 AM· committed by Julius Marmingeparentd9cce64
2 files changedLine totals unavailable