Replace the manual state-dict + per-resource branching teardown in
DockerBottleBackend.launch with an ExitStack: each resource registers
its own cleanup callback at the moment it's created, and stack.close()
unwinds in LIFO order. The previous form had to hand-coordinate four
nullable slots and re-check existence for the container; ExitStack
encodes the same semantics declaratively.
didericis
4fc0707760