Ensure await all on stdout does not deadlock

Editor assessment

Ensure await all on stdout does not deadlock is a specific regression-guard subject: it names the operation combination and the failure being guarded against, which is precisely what a test commit should communicate. The cli scope and test type are accurate, the imperative phrasing is clean, and no body is needed for an addition whose purpose the subject already states. No footer is required. Clear and correct, a serviceable publishable example. Adding the symptom the deadlock produced would have been the only improvement available to a subject that already states the guard's purpose.