diff --git a/contracts/agents-api/index.md b/contracts/agents-api/index.md
index f5eed41ba..f38f4a57e 100644
--- a/contracts/agents-api/index.md
+++ b/contracts/agents-api/index.md
@@ -37,7 +37,7 @@ Evidence for a status comes from the pinned official SDK and raw HTTP against th
 | Items | list | Partial: messages, commands, MCP calls, functions, web search, reasoning and Subagent coordination Items; other native variants are not projected | [Turns and Items](./sessions-events.md#turns-and-items) |
 | Artifacts | retrieve, list, delete, content | Implemented | [Environment files and Artifacts](./environment-files.md) |
 | Subagents | retrieve, list; Items; Turns retrieve and list; Turn Items | Partial: read-only child work; no live child progress or optional native operations | [Subagents](./subagents.md) |
-| Environments | retrieve | Implemented | [Environments](./environments.md) |
+| Environments | retrieve | Implemented; Session-scoped ([ownership](./environments.md#resources-and-states)). The pinned contract rejects `environment.environment_id`; existing hosted Environments cannot be attached across Sessions. Workspaces shared across Sessions belong to the application ([Projects own assets](../../docs/concepts.md#projects-own-assets)) | [Environments](./environments.md) |
 | Environment files | create, list | Implemented; the list is not recursive | [Environment files and Artifacts](./environment-files.md) |
 | Environment Templates | create, retrieve, update, list, delete | Implemented; execution limits are listed under [known gaps](#known-gaps) | [Environment Templates](./environments.md#templates) |
 | Vaults | create, retrieve, list, delete | Implemented; no archive operation | [Vaults and Credentials](./vaults.md) |
diff --git a/contracts/agents-api/zh/index.md b/contracts/agents-api/zh/index.md
index 9d55afff7..12ba940de 100644
--- a/contracts/agents-api/zh/index.md
+++ b/contracts/agents-api/zh/index.md
@@ -1,7 +1,7 @@
 ---
 title: "Agents API 覆盖台账"
 source: contracts/agents-api/index.md
-source_hash: 2394633ee55b7f86d374d5ab3827d0168d3dcbae8b962115063613e288b4cfda
+source_hash: 37355fa7100a2610ef727a3bb28f028d175be1b48b2d9f81c89b40f14cf17aef
 ---
 
 Core 旨在以下方固定版本为准支持完整的 OpenAI Agents API（[public API rule](https://github.com/MiniMax-AI/OpenAgentCore/blob/main/AGENTS.md#public-api)）。本台账记录 Core 对各项资源实现了哪些内容、哪些契约保存其详细信息，并列出相对于 OpenAI 服务的所有已知差异和所有未解决缺口。[API namespaces and credentials](../../../docs/zh/api/index.md) 说明谁调用哪些 API；[Agents API guide](../../../docs/zh/api/public-agent-api.md) 介绍使用方法。
@@ -40,7 +40,7 @@ Go 输入投影排除 `packages.system`，保留下方记录的明确拒绝行
 | Items | list | 部分实现：支持消息、命令、MCP 调用、functions、web search、reasoning 和 Subagent 协调 Items；其他原生变体不会被投影 | [Turns and Items](sessions-events.md#turns-and-items) |
 | Artifacts | retrieve, list, delete, content | 已实现 | [Environment files and Artifacts](environment-files.md) |
 | Subagents | retrieve, list; Items; Turns retrieve and list; Turn Items | 部分实现：只读子级工作；不支持实时子级进度或可选原生操作 | [Subagents](subagents.md) |
-| Environments | retrieve | 已实现 | [Environments](environments.md) |
+| Environments | retrieve | 已实现；以 Session 为范围（[归属](environments.md#resources-and-states)）。固定版本契约会拒绝 `environment.environment_id`；已有 hosted Environment 无法跨 Session 关联。跨 Session 共享的工作区属于应用（[Project 拥有资产](../../../docs/zh/concepts.md#projects-own-assets)） | [Environments](environments.md) |
 | Environment files | create, list | 已实现；列表不会递归 | [Environment files and Artifacts](environment-files.md) |
 | Environment Templates | create, retrieve, update, list, delete | 已实现；执行限制列于 [known gaps](#known-gaps) | [Environment Templates](environments.md#templates) |
 | Vaults | create, retrieve, list, delete | 已实现；没有归档操作 | [Vaults and Credentials](vaults.md) |
diff --git a/services/core/internal/api/hosted_environment_test.go b/services/core/internal/api/hosted_environment_test.go
index 322223cca..ea3df0f10 100644
--- a/services/core/internal/api/hosted_environment_test.go
+++ b/services/core/internal/api/hosted_environment_test.go
@@ -11,6 +11,7 @@ import (
 	"testing"
 
 	"github.com/MiniMax-AI/OpenAgentCore/services/core/internal/sessions"
+	"github.com/google/uuid"
 )
 
 func TestHostedEnvironmentDefaultsAndExplicitGaps(t *testing.T) {
@@ -42,6 +43,26 @@ func TestHostedEnvironmentDefaultsAndExplicitGaps(t *testing.T) {
 	}
 }
 
+// The pinned openai_hosted input has no environment_id, so a request naming an
+// existing Environment gets the route's existing error instead of a new
+// Environment, with or without a Template.
+func TestSessionCreationRejectsExistingEnvironmentReference(t *testing.T) {
+	h, s := validationHandler(t)
+	rejected := `{"error":{"message":"Request fields have invalid types or null values.","type":"invalid_request_error","code":"invalid_request","param":null}}` + "\n"
+	for _, environment := range []string{
+		`{"type":"openai_hosted","environment_id":"` + uuid.NewString() + `"}`,
+		`{"type":"openai_hosted","environment_id":"` + uuid.NewString() + `","environment_template_id":"` + uuid.NewString() + `"}`,
+	} {
+		body := `{"agent":{"model":"m"},"environment":` + environment + `,"input":"hi"}`
+		if w := bodyGateRequest(h, "/v1/agents/sessions", "application/json", []byte(body)); w.Code != http.StatusBadRequest || w.Body.String() != rejected {
+			t.Errorf("%s: %d %s", environment, w.Code, w.Body)
+		}
+	}
+	if s.writes != 0 {
+		t.Fatalf("an Environment reference reached storage: %d writes", s.writes)
+	}
+}
+
 func TestHostedEnvironmentResponseHasPinnedShapeAndNoConnectionAction(t *testing.T) {
 	s := environmentSession()
 	s.Configuration = json.RawMessage(`{"agent":{"id":"agent","model":"model"},"environment":{"type":"openai_hosted"}}`)