fix(gateway): normalize model alias billing identity

apps/api/internal/store/candidates_test.go

@@ -2,6 +2,52 @@ package store
 
 import "testing"
 
+func TestNormalizeModelMatchKeyRemovesWhitespace(t *testing.T) {
+	got := normalizeModelMatchKey(" doubao-5.0 图像\t编辑\n")
+	if got != "doubao-5.0图像编辑" {
+		t.Fatalf("expected whitespace-insensitive model key, got %q", got)
+	}
+}
+
+func TestTaskBillingModelIdentityPrefersSystemAlias(t *testing.T) {
+	identity := taskBillingModelIdentity(GatewayTask{
+		Model:          "doubao-5.0 图像编辑",
+		RequestedModel: "doubao-5.0 图像编辑",
+		ResolvedModel:  "doubao-image-real",
+		Metrics: map[string]any{
+			"modelAlias":    "doubao-5.0图像编辑",
+			"modelName":     "doubao-image-real",
+			"providerModel": "doubao-provider-image",
+		},
+	})
+
+	if identity.Model != "doubao-5.0图像编辑" || identity.ResolvedModel != "doubao-5.0图像编辑" {
+		t.Fatalf("expected persisted model to use system alias, got %+v", identity)
+	}
+	if identity.RequestedModel != "doubao-5.0 图像编辑" {
+		t.Fatalf("expected requested model to preserve original request, got %+v", identity)
+	}
+	if identity.ModelName != "doubao-image-real" || identity.ProviderModelName != "doubao-provider-image" {
+		t.Fatalf("expected model name/provider model to stay available, got %+v", identity)
+	}
+}
+
+func TestTaskBillingModelIdentityFallsBackToBillingLines(t *testing.T) {
+	identity := taskBillingModelIdentity(GatewayTask{
+		Model: "front end alias",
+		Billings: []any{
+			map[string]any{
+				"model":      "system-model-name",
+				"modelAlias": "System Model Alias",
+			},
+		},
+	})
+
+	if identity.Model != "System Model Alias" || identity.ModelName != "system-model-name" {
+		t.Fatalf("expected billing lines to provide system model identity, got %+v", identity)
+	}
+}
+
 func TestRuntimeCandidateLoadUsesMaxLimitedMetric(t *testing.T) {
 	candidate := RuntimeModelCandidate{}
 	applyRuntimeCandidateLoad(&candidate, runtimeCandidateLoadInput{