The demo was scaffolding, not repo content: nothing referenced it but a
docstring.
The tests were 12 against the repo's 1-2 invariant bar. Keep the two that fail
silently when inverted -- the sentinel reaching an exec'd child (the unexported
variable this change fixes) and the prologue's staleness gate, which inverted
either way costs a re-sync per run or a stale environment that looks fine. The
per-OS command pair stays because neither host can observe the other's string.
Dropped the exit-code/message restatement, the no-sentinel cold path, and the
demo-driven harness.
1ec55baea8