matchmaking now queues. the first player in waits, the second one to
arrive pairs with them, and both get the same battle: one shared session
keyed by both accounts, one snapshot, the client working out which side
it is from the account ids it already carries. if nobody turns up within
ten seconds the ticker polls the queue out and builds the bot battle
instead. cancelling or disconnecting leaves the queue.
also fixes the movement component tail: the extracted layout counts
"n + 18" vints including the path length itself, so seventeen follow the
path, not eighteen. the verifier read one too many and every snapshot
carrying a moving unit came apart after it - which is what the guard
caught and refused to send, rather than the client aborting on it.
ba235a9b4c