fix(gateway): put the opened game on the wire even when the enqueue is not yet matched

The real cause of 'Start game does not enter the game': encodeMatch gated the MatchResult game on matched (matched := m.Matched && m.Game != nil), so an open game awaiting an opponent (matched=false, game set) lost its game on the wire and the client had nothing to navigate into. Encode the game whenever m.Game is present; the backend's matched flag is authoritative. Regression test added (matched=false + game reaches the wire). The earlier codec fix guarded the same drop on the decode side.

gateway/internal/transcode/transcode_test.go

@@ -114,6 +114,36 @@ func TestEnqueueRoundTripEncodesMatch(t *testing.T) {
 	}
 }
 
+func TestEnqueueEncodesOpenGameWhenNotMatched(t *testing.T) {
+	// An auto-match enqueue that opens a game awaiting an opponent returns matched=false but
+	// still carries the game; it must reach the client so it navigates into the game at once.
+	backend, cleanup := fakeBackend(t, func(w http.ResponseWriter, r *http.Request) {
+		_, _ = w.Write([]byte(`{"matched":false,"game":{"id":"g-open","variant":"scrabble_en","status":"open","players":2,"to_move":0,"seats":[]}}`))
+	})
+	defer cleanup()
+
+	reg := transcode.NewRegistry(backend, nil)
+	op, _ := reg.Lookup(transcode.MsgLobbyEnqueue)
+
+	b := flatbuffers.NewBuilder(32)
+	v := b.CreateString("scrabble_en")
+	fb.EnqueueRequestStart(b)
+	fb.EnqueueRequestAddVariant(b, v)
+	b.Finish(fb.EnqueueRequestEnd(b))
+
+	payload, err := op.Handler(context.Background(), transcode.Request{Payload: b.FinishedBytes(), UserID: "u-1"})
+	if err != nil {
+		t.Fatalf("handler: %v", err)
+	}
+	m := fb.GetRootAsMatchResult(payload, 0)
+	if m.Matched() {
+		t.Fatal("an open game awaiting an opponent must report matched=false")
+	}
+	if g := m.Game(nil); g == nil || string(g.Id()) != "g-open" {
+		t.Fatalf("open game must be on the wire even when not matched: %+v", g)
+	}
+}
+
 func TestDomainErrorSurfacesBackendCode(t *testing.T) {
 	backend, cleanup := fakeBackend(t, func(w http.ResponseWriter, r *http.Request) {
 		w.WriteHeader(http.StatusConflict)