Fix New Workspace PR worktree creation (#1565)

* Fix PR worktree creation from New Workspace

* Use fixture default branch in GitHub E2E clone

packages/app/src/screens/new-workspace-picker-item.ts

@@ -20,11 +20,13 @@ export function pickerItemToCheckoutRequest(
   switch (item.kind) {
     case "branch":
       return { action: "branch-off", refName: item.name };
-    case "github-pr":
+    case "github-pr": {
+      const headRefName = item.item.headRefName?.trim();
       return {
         action: "checkout",
-        refName: item.item.headRefName ?? "",
+        ...(headRefName ? { refName: headRefName } : {}),
         githubPrNumber: item.item.number,
       };
+    }
   }
 }

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

@@ -804,8 +804,8 @@ async function createMultiplicityWorkspace(input: {
   createFailedMessage: string;
 }): Promise<ReturnType<typeof normalizeWorkspaceDescriptor>> {
   const isWorktree = input.isolation === "worktree";
-  const baseBranch = isWorktree
-    ? (resolveCheckoutRequest(input.selectedItem, input.currentBranch)?.refName ?? undefined)
+  const checkoutRequest = isWorktree
+    ? resolveCheckoutRequest(input.selectedItem, input.currentBranch)
     : undefined;
   const firstAgentContext = buildFirstAgentContext({
     prompt: input.prompt,
@@ -818,7 +818,7 @@ async function createMultiplicityWorkspace(input: {
           cwd: input.project.iconWorkingDir,
           projectId: input.project.projectKey,
           worktreeSlug: createNameId(),
-          ...(baseBranch ? { baseBranch } : {}),
+          ...checkoutRequest,
         }
       : {
           kind: "directory",