Does a failed Poetry self update replace the previous binary atomically?

Goal

I need to know whether a failed Poetry self-upgrade leaves the previous executable available or replaces it in place, and whether that depends on the installation method.

Poetry updates itself through `poetry self update`, but it is unclear whether the update is atomic across the standalone installer, pipx, pip, or system package manager. A partial update can leave the `poetry` command unresponsive, and Poetry has no built-in self-rollback command. Behavior may also differ between Poetry 1.x and 2.x.

Because the original installation channel determines how a known-good version can be restored, I need to clarify the failure semantics before choosing a recovery path.

Does a failed `poetry self update` preserve the previous binary? Does the behavior differ by installation method or Poetry major version?