chore(cleanup): purge /command residuals — fakeEngine, canon golden, openapi

Follow-up tidy after the cross-service /command removal (#73):

- Rename the router test double dummyExecutor -> fakeEngine (and the
  newExecutor / setupRouterExecutor helpers -> newFakeEngine /
  setupRouterEngine): it implements handler.Engine now, "executor" was a
  leftover of the removed adapter. Test-only.

- Regenerate the ui/core canon signing golden onto user.games.order
  (request_user_games_command.json -> request_user_games_order.json, fresh
  canonical bytes + Ed25519 signature) and drop the last
  user.games.command references from the Go/TS tests and docs.

- Align game openapi: CommandRequest.cmd no longer carries minItems: 1. It
  is now used only by PUT /api/v1/order, which accepts an empty batch
  (clearing the player's stored order, equivalent to removing every
  command); the contract test freezes the empty-allowed shape.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

game/internal/router/order_test.go

@@ -68,8 +68,8 @@ func TestOrderRaceQuit(t *testing.T) {
 	payload = &rest.Command{
 		Actor: commandDefaultActor,
 	}
-	exec := &dummyExecutor{}
-	emptyRouter := setupRouterExecutor(exec)
+	exec := &fakeEngine{}
+	emptyRouter := setupRouterEngine(exec)
 
 	w = httptest.NewRecorder()
 	req, _ = http.NewRequest(apiCommandMethod, apiOrderPath, asBody(payload))
@@ -927,8 +927,8 @@ func TestOrderPlanetRouteRemove(t *testing.T) {
 }
 
 func TestMultipleCommandOrder(t *testing.T) {
-	e := newExecutor()
-	r := setupRouterExecutor(e)
+	e := newFakeEngine()
+	r := setupRouterEngine(e)
 
 	payload := &rest.Command{
 		Actor: commandDefaultActor,
@@ -951,11 +951,11 @@ func TestMultipleCommandOrder(t *testing.T) {
 
 	assert.Equal(t, commandNoErrorsStatus, w.Code, w.Body)
 
-	assert.Equal(t, 2, e.(*dummyExecutor).CommandsExecuted)
+	assert.Equal(t, 2, e.(*fakeEngine).CommandsExecuted)
 }
 
 func TestPutOrderResponseBody(t *testing.T) {
-	e := &dummyExecutor{
+	e := &fakeEngine{
 		ValidateOrderResult: &order.UserGamesOrder{
 			GameID:    uuid.New(),
 			UpdatedAt: 1700,
@@ -967,7 +967,7 @@ func TestPutOrderResponseBody(t *testing.T) {
 			},
 		},
 	}
-	r := setupRouterExecutor(e)
+	r := setupRouterEngine(e)
 
 	payload := &rest.Command{
 		Actor: commandDefaultActor,
@@ -997,8 +997,8 @@ func TestPutOrderResponseBody(t *testing.T) {
 }
 
 func TestPutOrderEngineError(t *testing.T) {
-	e := &dummyExecutor{ValidateOrderErr: errors.New("engine boom")}
-	r := setupRouterExecutor(e)
+	e := &fakeEngine{ValidateOrderErr: errors.New("engine boom")}
+	r := setupRouterEngine(e)
 
 	payload := &rest.Command{
 		Actor: commandDefaultActor,
@@ -1054,8 +1054,8 @@ func TestPutOrderPerCommandRejection(t *testing.T) {
 			},
 		},
 	}
-	executor := &dummyExecutor{ValidateOrderResult: result}
-	r := setupRouterExecutor(executor)
+	executor := &fakeEngine{ValidateOrderResult: result}
+	r := setupRouterEngine(executor)
 
 	payload := &rest.Command{
 		Actor: commandDefaultActor,
@@ -1112,8 +1112,8 @@ func TestPutOrderPerCommandRejection(t *testing.T) {
 // *GenericError on the input shelf, which must map to HTTP 400 with
 // the `{"generic_error","code"}` envelope rather than 500.
 func TestPutOrderStructuralRejection(t *testing.T) {
-	executor := &dummyExecutor{ValidateOrderErr: e.NewQuitCommandFollowedByCommandError()}
-	r := setupRouterExecutor(executor)
+	executor := &fakeEngine{ValidateOrderErr: e.NewQuitCommandFollowedByCommandError()}
+	r := setupRouterEngine(executor)
 
 	payload := &rest.Command{
 		Actor: commandDefaultActor,
@@ -1152,8 +1152,8 @@ func TestGetOrderQueryValidation(t *testing.T) {
 		{"Non-numeric turn", "?player=Race_01&turn=abc", http.StatusBadRequest},
 	} {
 		t.Run(tc.description, func(t *testing.T) {
-			e := &dummyExecutor{}
-			r := setupRouterExecutor(e)
+			e := &fakeEngine{}
+			r := setupRouterEngine(e)
 
 			w := httptest.NewRecorder()
 			req, _ := http.NewRequest(http.MethodGet, apiOrderPath+tc.query, nil)
@@ -1176,11 +1176,11 @@ func TestGetOrderFound(t *testing.T) {
 			},
 		},
 	}
-	e := &dummyExecutor{
+	e := &fakeEngine{
 		FetchOrderResult: stored,
 		FetchOrderOK:     true,
 	}
-	r := setupRouterExecutor(e)
+	r := setupRouterEngine(e)
 
 	w := httptest.NewRecorder()
 	req, _ := http.NewRequest(http.MethodGet, apiOrderPath+"?player=Race_01&turn=3", nil)
@@ -1202,11 +1202,11 @@ func TestGetOrderFound(t *testing.T) {
 }
 
 func TestGetOrderTurnDefaultsToZero(t *testing.T) {
-	e := &dummyExecutor{
+	e := &fakeEngine{
 		FetchOrderResult: &order.UserGamesOrder{GameID: uuid.New(), UpdatedAt: 1, Commands: []order.DecodableCommand{}},
 		FetchOrderOK:     true,
 	}
-	r := setupRouterExecutor(e)
+	r := setupRouterEngine(e)
 
 	w := httptest.NewRecorder()
 	req, _ := http.NewRequest(http.MethodGet, apiOrderPath+"?player=Race_01", nil)
@@ -1217,8 +1217,8 @@ func TestGetOrderTurnDefaultsToZero(t *testing.T) {
 }
 
 func TestGetOrderNotFound(t *testing.T) {
-	e := &dummyExecutor{FetchOrderOK: false}
-	r := setupRouterExecutor(e)
+	e := &fakeEngine{FetchOrderOK: false}
+	r := setupRouterEngine(e)
 
 	w := httptest.NewRecorder()
 	req, _ := http.NewRequest(http.MethodGet, apiOrderPath+"?player=Race_01&turn=2", nil)
@@ -1231,8 +1231,8 @@ func TestGetOrderNotFound(t *testing.T) {
 }
 
 func TestGetOrderEngineError(t *testing.T) {
-	e := &dummyExecutor{FetchOrderErr: errors.New("engine boom")}
-	r := setupRouterExecutor(e)
+	e := &fakeEngine{FetchOrderErr: errors.New("engine boom")}
+	r := setupRouterEngine(e)
 
 	w := httptest.NewRecorder()
 	req, _ := http.NewRequest(http.MethodGet, apiOrderPath+"?player=Race_01&turn=0", nil)