enable --now does not restart an already-running unit

NS-005 observedno-op-reported-as-action

reads as: The command exits zero and the service is active. Conclusion drawn: the new code is live.
actually: systemctl enable --now starts a stopped unit. On a running one it is a no-op. The old process, with the old ExecStart, survives.
blind because: Exit code zero and `active (running)` are true statements about the wrong process.
the check: Compare the unit's ExecStart on disk against the live process: systemctl show -p ExecStart NAME and ps -p $MAINPID -o args=
cost of missing: A deploy is reported as complete twice while the previous binary keeps serving.
generalises to: Any idempotent-looking command whose semantics differ by current state.

Reported as

NS-008 — set -e aborts a script at a validation step that concerns something else
NS-013 — A teardown script destroys the environment it is executing inside
NS-014 — A privilege prompt with nowhere to appear hangs instead of failing
NS-015 — A pipeline returns the status of its last command, not its failing one
NS-016 — curl exits zero after successfully downloading an error page