R7: per-player transports + drop finished games in the load harness

Each virtual player now builds its own edge.Client (its own h2c connection
carrying both the Subscribe stream and the Execute calls), instead of every
player multiplexing over a single shared http2.Transport. The R2 trip report
traced the ~14% transport_error on game.state at 500 players to that single
shared transport; per-player connections mirror real clients and isolate the
artifact. The assembly burst and the gateway-hammer each get their own client.

playTurn now reports when a game has finished so playerLoop drops it from the
rotation (slices.DeleteFunc); once no active game remains the player idles while
still holding its stream. This stops secondary ops from hammering game_finished
on already-ended games (the other R2 harness finding).

loadtest/internal/edge/client.go

@@ -41,16 +41,18 @@ const (
 	msgEnqueue    = "lobby.enqueue"
 )
 
-// Client speaks the edge protocol to a single gateway base URL over h2c. It is safe
-// for concurrent use by many virtual players (the underlying http2.Transport pools
-// and multiplexes connections).
+// Client speaks the edge protocol to a single gateway base URL over h2c. The harness
+// builds one Client per virtual player, so each player owns its h2c connection (its
+// Subscribe stream and Execute calls share it) the way a real client does; a single
+// Client is safe for that player's own concurrent goroutines.
 type Client struct {
 	rpc edgev1connect.GatewayClient
 }
 
 // New builds a Client for baseURL (for example http://gateway:8081). The transport
 // speaks HTTP/2 cleartext (h2c) to match the gateway, dialling plaintext TCP rather
-// than TLS.
+// than TLS. Each virtual player gets its own Client (hence its own connection), so the
+// load mirrors real clients instead of multiplexing every player over one transport.
 func New(baseURL string) *Client {
 	hc := &http.Client{
 		Transport: &http2.Transport{