feat(FN-4298): complete Step 2 — reset worktree liveness mock defaults

Fusion-Task-Id: FN-4298
Fusion-Task-Lineage: 25d48169-58be-42f9-aafc-4b47db554e57

packages/engine/src/__tests__/executor-test-helpers.ts

@@ -320,6 +320,7 @@ export function createMockStore() {
 
 export function resetExecutorMocks() {
   vi.clearAllMocks();
+  mockedIsUsableTaskWorktree.mockResolvedValue(true);
   mockExecuteAll.mockResolvedValue([]);
   mockTerminateAllSessions.mockResolvedValue(undefined);
   mockCleanup.mockResolvedValue(undefined);