Previously POST returned only { id, name }, while GET returns
{ id, name, state, lastOutputAt }. iOS clients that share a Decodable
for both endpoints (e.g. SessionItem in pi-remote-ios) failed to decode
the POST response with 'data couldn't be read because it is missing'.
The new session always starts in 'idle' state with empty lastOutputAt.
Documented the new shape in the route header comment.
jay
Johannes Merz