## Summary
**Changes made:**
1. **Added `useMemo` import** (line 1) for memoizing the filtered options array
2. **Added logic to hide "Open pull request" when PR is open** (lines 101-109):
- `hasPrOpen` checks if `prStatus === 'open'`
- `availableActionOptions` filters out the 'pull-request' option when a PR is already open
3. **Added fallback for selected action** (lines 111-113):
- `effectiveSelectedAction` ensures that if the user had previously selected 'pull-request' but a PR is now open, the button shows 'Merge' instead
4. **Updated SplitButton** to use `availableActionOptions` and `effectiveSelectedAction` (lines 286-291)
**Behavior:**
- When there is no open PR: Both "Open pull request" and "Merge" options are available
- When there is an open PR (`prStatus === 'open'`): Only the "Merge" option is shown
- When PR is closed or merged: The "Open pull request" option reappears (allowing users to create a new PR)
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