fix(app): select current branch for new workspaces

Closes #541

packages/app/src/screens/new-workspace-screen.test.tsx

@@ -97,7 +97,11 @@ const {
 
   const hoistedMockClient = {
     isConnected: true,
-    getCheckoutStatus: vi.fn(async () => ({ currentBranch: "main" })),
+    getCheckoutStatus: vi.fn(
+      async (): Promise<{ currentBranch: string | null }> => ({
+        currentBranch: "main",
+      }),
+    ),
     getBranchSuggestions: vi.fn(async () => ({ branches: ["main", "dev", "feat/x"] })),
     searchGitHub: vi.fn(async () => ({
       items: [hoistedPrItem, hoistedPrItemB],
@@ -672,7 +676,7 @@ describe("NewWorkspaceScreen picker payload", () => {
     });
   });
 
-  it("sends no new fields when nothing is selected (default)", async () => {
+  it("uses the loaded current branch as the selected branch", async () => {
     renderScreen();
     await flush();
 
@@ -684,12 +688,24 @@ describe("NewWorkspaceScreen picker payload", () => {
     expect(call).toMatchObject({
       cwd: "/repo",
       worktreeSlug: "gentle-slug",
+      action: "branch-off",
+      refName: "main",
     });
-    expect(call).not.toHaveProperty("refName");
-    expect(call).not.toHaveProperty("action");
     expect(call).not.toHaveProperty("githubPrNumber");
   });
 
+  it("requires a branch selection when the current branch is unavailable", async () => {
+    mockClient.getCheckoutStatus.mockResolvedValueOnce({ currentBranch: null });
+    renderScreen();
+    await flush();
+
+    click(await findByTestId("test-composer-submit"));
+    await flush();
+
+    expect(mockClient.createPaseoWorktree).not.toHaveBeenCalled();
+    expect(document.body.textContent).toContain("Choose a branch to start from");
+  });
+
   it("opens the new workspace draft tab as soon as the worktree is ready", async () => {
     initialDraftState.text = "please review this change";
     renderScreen();

packages/app/src/screens/new-workspace-screen.tsx

@@ -194,6 +194,15 @@ function pickerItemTriggerLabel(item: PickerItem): string {
   return item.kind === "branch" ? item.name : formatPrLabel(item.item);
 }
 
+function resolveSelectedPickerItem(input: {
+  pickerSelection: PickerSelection | null;
+  currentBranch: string | null | undefined;
+}): PickerItem | null {
+  if (input.pickerSelection) return input.pickerSelection.item;
+  const currentBranch = input.currentBranch?.trim();
+  return currentBranch ? { kind: "branch", name: currentBranch } : null;
+}
+
 function syncPickerPrAttachment(input: {
   attachments: ComposerAttachment[];
   previousPickerPrNumber: number | null;
@@ -436,7 +445,6 @@ export function NewWorkspaceScreen({
 
   const displayName = displayNameProp?.trim() ?? "";
   const workspace = createdWorkspace;
-  const selectedItem = pickerSelection?.item ?? null;
   const isPending = pendingAction !== null;
   const client = useHostRuntimeClient(serverId);
   const isConnected = useHostRuntimeIsConnected(serverId);
@@ -476,7 +484,10 @@ export function NewWorkspaceScreen({
     refetchOnWindowFocus: false,
   });
 
-  const currentBranch = checkoutStatusQuery.data?.currentBranch ?? null;
+  const selectedItem = resolveSelectedPickerItem({
+    pickerSelection,
+    currentBranch: checkoutStatusQuery.data?.currentBranch,
+  });
 
   const branchSuggestionsQuery = useQuery({
     queryKey: ["branch-suggestions", serverId, sourceDirectory, debouncedPickerSearchQuery],
@@ -527,8 +538,8 @@ export function NewWorkspaceScreen({
 
   const triggerLabel = useMemo(() => {
     if (selectedItem) return pickerItemTriggerLabel(selectedItem);
-    return currentBranch ?? "main";
-  }, [currentBranch, selectedItem]);
+    return "Select branch";
+  }, [selectedItem]);
 
   const selectedOptionId = useMemo(() => {
     if (!selectedItem) return "";
@@ -588,6 +599,9 @@ export function NewWorkspaceScreen({
   const buildCreateWorktreeInput = useCallback(
     (input: { cwd: string; attachments: AgentAttachment[] }) => {
       const checkoutRequest = pickerItemToCheckoutRequest(selectedItem);
+      if (!checkoutRequest) {
+        throw new Error("Choose a branch to start from");
+      }
 
       return {
         cwd: input.cwd,