Update an automation

Changes an automation, including the graph. Needs sending: write, and is a write.

steps replaces the whole graph. Leaving it out leaves the graph alone, which is what a rename is. Sending it replaces it entirely, and every gate the create runs runs again.

An edit applies to the runs already in flight. A run sits on a step id, so a subscriber part way through the sequence picks up the new steps from wherever they are. That is the point of editing a live automation rather than replacing it.

It is also why removing a step can answer 409. If runs are waiting on a step this edit removes, the request is refused with how many and on which steps, because removing it would leave those subscribers part way through with nothing to advance them and nothing reporting it. Send on_removed_step to say what should happen: "exit" ends those runs, or a step id from the graph you are sending moves them there.

Publishes no event.