diff --git a/app/gateway/models.py b/app/gateway/models.py
index aa40032..16f8b8d 100644
--- a/app/gateway/models.py
+++ b/app/gateway/models.py
@@ -6,10 +6,10 @@ intent 字段刻意保留成 `dict[str, Any]`——网关不解释下单意图
 """
 from __future__ import annotations
 
-from typing import Any
+from typing import Annotated, Any
 from urllib.parse import urlsplit
 
-from pydantic import BaseModel, Field, field_validator
+from pydantic import BaseModel, Field, WithJsonSchema, field_validator
 
 from app.shared.task_state import AccountQueryKind, OrderState, QueryStatus, TaskStatus
 
@@ -17,6 +17,79 @@ from app.shared.task_state import AccountQueryKind, OrderState, QueryStatus, Tas
 # ---- POST /api/orders ----
 
 
+# The gateway intentionally keeps intent open-ended at runtime. This schema documents
+# the stable trading fields without preventing future fields from being passed through.
+OrderIntent = Annotated[
+    dict[str, Any],
+    WithJsonSchema(
+        {
+            "type": "object",
+            "additionalProperties": True,
+            "description": (
+                "下单意图。推荐使用 items；旧版 item_url 等同级字段继续兼容。"
+            ),
+            "properties": {
+                "items": {
+                    "type": "array",
+                    "minItems": 1,
+                    "description": "本次购买的商品列表，按顺序加入同一购物车",
+                    "items": {
+                        "oneOf": [
+                            {
+                                "type": "object",
+                                "additionalProperties": True,
+                                "properties": {
+                                    "item_url": {
+                                        "type": "string",
+                                        "description": "商品页 URL",
+                                    },
+                                    "quantity": {
+                                        "type": "integer",
+                                        "minimum": 1,
+                                        "default": 1,
+                                    },
+                                    "variant_id": {"type": "string"},
+                                    "choice": {
+                                        "oneOf": [
+                                            {"type": "string"},
+                                            {
+                                                "type": "array",
+                                                "items": {"type": "string"},
+                                            },
+                                        ]
+                                    },
+                                },
+                                "required": ["item_url"],
+                            },
+                            {
+                                "type": "string",
+                                "description": "商品页 URL（简写）",
+                            },
+                        ]
+                    },
+                },
+                "item_url": {
+                    "type": "string",
+                    "description": "旧版单商品商品页 URL",
+                },
+                "quantity": {"type": "integer", "minimum": 1, "default": 1},
+                "variant_id": {"type": "string"},
+                "choice": {
+                    "oneOf": [
+                        {"type": "string"},
+                        {"type": "array", "items": {"type": "string"}},
+                    ]
+                },
+                "max_total_yen": {
+                    "type": "integer",
+                    "description": "本次订单允许的最高应付金额（日元）",
+                },
+            },
+        }
+    ),
+]
+
+
 class SubmitOrderRequest(BaseModel):
     """上游提交下单意图
 
@@ -34,7 +107,7 @@ class SubmitOrderRequest(BaseModel):
         description="站点标识。交易服务只覆盖乐天市场，固定 rakuten",
         examples=["rakuten"],
     )
-    intent: dict[str, Any] = Field(
+    intent: OrderIntent = Field(
         description=(
             "下单意图原文。网关不解释内容，原样存库并透传给本地 worker，结构由 trading 侧定义："
             "推荐使用 items（非空数组，每项含 item_url，及可选 quantity/variant_id/choice）；"
@@ -50,6 +123,9 @@ class SubmitOrderRequest(BaseModel):
                 "item_url": "https://item.rakuten.co.jp/shop/code/",
                 "quantity": 1,
                 "variant_id": "1001",
+            }, {
+                "item_url": "https://item.rakuten.co.jp/shop/another-code/",
+                "quantity": 2,
             }],
             "max_total_yen": 30000,
         }],
diff --git a/tests/test_openapi_export.py b/tests/test_openapi_export.py
index 95057c7..3fda640 100644
--- a/tests/test_openapi_export.py
+++ b/tests/test_openapi_export.py
@@ -103,3 +103,16 @@ def test_all_refs_resolve(spec):
     names = set(spec["components"]["schemas"])
     refs = set(re.findall(r"#/components/schemas/([^\"]+)", json.dumps(spec)))
     assert not refs - names
+
+
+def test_submit_order_intent_schema_documents_multi_item_and_legacy_fields(spec):
+    """intent 保持透传对象，同时在 OpenAPI 中明确展示新旧两种商品格式。"""
+    intent = spec["components"]["schemas"]["SubmitOrderRequest"]["properties"]["intent"]
+    properties = intent["properties"]
+    assert intent["additionalProperties"] is True
+    assert properties["items"]["type"] == "array"
+    assert properties["items"]["minItems"] == 1
+    item_object = properties["items"]["items"]["oneOf"][0]
+    assert item_object["required"] == ["item_url"]
+    assert "item_url" in properties
+    assert "quantity" in properties