diff --git a/backend/crates/gateway-core/src/engine/middleware/contract.rs b/backend/crates/gateway-core/src/engine/middleware/contract.rs
index e6479db24..91f71c363 100644
--- a/backend/crates/gateway-core/src/engine/middleware/contract.rs
+++ b/backend/crates/gateway-core/src/engine/middleware/contract.rs
@@ -104,7 +104,6 @@ impl fmt::Debug for MiddlewareHeader {
 #[derive(Clone, PartialEq, Eq)]
 pub struct MiddlewareRequest {
     settings: Option<RequestSettings>,
-    provider_parameters: Option<serde_json::Map<String, serde_json::Value>>,
     protocol: String,
     headers: Vec<MiddlewareHeader>,
     body: Bytes,
@@ -126,7 +125,6 @@ impl MiddlewareRequest {
         let protocol = protocol.into();
         Self {
             settings: None,
-            provider_parameters: None,
             original_protocol: protocol.clone(),
             original_body: body.clone(),
             capabilities: None,
@@ -147,27 +145,6 @@ impl MiddlewareRequest {
         self.settings.as_ref()
     }
 
-    /// Provider 提供的本次构造参数；Core 不解释其中的业务字段
-    #[must_use]
-    pub fn provider_parameters(&self) -> Option<&serde_json::Map<String, serde_json::Value>> {
-        self.provider_parameters.as_ref()
-    }
-
-    #[must_use]
-    pub fn with_provider_parameters(
-        mut self,
-        parameters: serde_json::Map<String, serde_json::Value>,
-    ) -> Self {
-        self.provider_parameters = Some(parameters);
-        self
-    }
-
-    pub fn take_provider_parameters(
-        &mut self,
-    ) -> Option<serde_json::Map<String, serde_json::Value>> {
-        self.provider_parameters.take()
-    }
-
     #[must_use]
     pub fn protocol(&self) -> &str {
         &self.protocol
diff --git a/backend/crates/gateway-core/src/engine/mod.rs b/backend/crates/gateway-core/src/engine/mod.rs
index e713c9e3a..cabee6dc1 100644
--- a/backend/crates/gateway-core/src/engine/mod.rs
+++ b/backend/crates/gateway-core/src/engine/mod.rs
@@ -755,7 +755,6 @@ impl AttemptContext {
         provider: ProviderKind,
         model: Option<String>,
         account_id: ProviderAccountId,
-        parameters: Option<serde_json::Map<String, serde_json::Value>>,
         terminal: provider::ProviderMiddlewareTerminal,
     ) -> Result<provider::ProviderStream, ProviderError> {
         // 入口已校验原请求，此处复查中间件最终提交的 operation，每次重试均生效
@@ -763,7 +762,7 @@ impl AttemptContext {
             .account_scope()
             .is_some_and(|scope| !scope.allows_image_generation())
         {
-            Box::new(move |operation, headers, parameters| {
+            Box::new(move |operation, headers| {
                 Box::pin(async move {
                     image_generation::check_image_generation(false, &operation).map_err(|_| {
                         ProviderError::new(
@@ -772,7 +771,7 @@ impl AttemptContext {
                         )
                         .with_retry_prohibited()
                     })?;
-                    terminal(operation, headers, parameters).await
+                    terminal(operation, headers).await
                 })
             })
         } else {
@@ -790,7 +789,6 @@ impl AttemptContext {
             context,
             operation,
             self.request.client_transport,
-            parameters,
             terminal,
         )
         .await
diff --git a/backend/crates/gateway-core/src/engine/provider.rs b/backend/crates/gateway-core/src/engine/provider.rs
index 1ae57ef58..90a8388a0 100644
--- a/backend/crates/gateway-core/src/engine/provider.rs
+++ b/backend/crates/gateway-core/src/engine/provider.rs
@@ -471,7 +471,6 @@ pub type ProviderMiddlewareTerminal = Box<
     dyn FnOnce(
             Operation,
             Vec<MiddlewareHeader>,
-            Option<serde_json::Map<String, serde_json::Value>>,
         ) -> BoxFuture<'static, Result<ProviderStream, ProviderError>>
         + Send
         + 'static,
@@ -490,19 +489,18 @@ fn provider_middleware_next(
     activate: oneshot::Receiver<()>,
     observation: Arc<Mutex<MiddlewareSendObservation>>,
 ) -> MiddlewareNext {
-    crate::middleware::compose(Vec::new(), move |mut request| {
+    crate::middleware::compose(Vec::new(), move |request| {
         Box::pin(async move {
             let fallback_protocol = operation.protocol().to_owned();
             if request.has_capability_declaration() {
                 return Err(MiddlewareError::InvalidState);
             }
-            let parameters = request.take_provider_parameters();
             let (protocol, headers, body) = request.into_parts();
             validate_attempt_headers(&headers)?;
             let operation = operation
                 .replace_middleware_wire(protocol, body)
                 .map_err(|_| MiddlewareError::InvalidState)?;
-            let stream = terminal(operation, headers, parameters)
+            let stream = terminal(operation, headers)
                 .await
                 .map_err(MiddlewareError::Provider)?;
             let metadata = stream.metadata().clone();
@@ -736,22 +734,18 @@ pub async fn execute_attempt_middleware(
     context: MiddlewareContext,
     operation: Operation,
     transport: ClientTransport,
-    parameters: Option<serde_json::Map<String, serde_json::Value>>,
     terminal: ProviderMiddlewareTerminal,
 ) -> Result<ProviderStream, ProviderError> {
     let Some(plan) = plan else {
-        return terminal(operation, Vec::new(), parameters).await;
+        return terminal(operation, Vec::new()).await;
     };
-    let mut request = MiddlewareRequest::new(
+    let request = MiddlewareRequest::new(
         operation.protocol(),
         Vec::<MiddlewareHeader>::new(),
         operation
             .middleware_body()
             .map_err(|_| middleware_protocol_error(UpstreamSendState::NotSent))?,
     );
-    if let Some(parameters) = parameters {
-        request = request.with_provider_parameters(parameters);
-    }
     let (prepared, metadata) = oneshot::channel();
     let (activate, activation) = oneshot::channel();
     let observation = Arc::new(Mutex::new(MiddlewareSendObservation {
diff --git a/backend/crates/gateway-core/tests/engine/execution/outbound.rs b/backend/crates/gateway-core/tests/engine/execution/outbound.rs
index c4d5449cd..0747a684e 100644
--- a/backend/crates/gateway-core/tests/engine/execution/outbound.rs
+++ b/backend/crates/gateway-core/tests/engine/execution/outbound.rs
@@ -103,8 +103,7 @@ impl Provider for PreparingProvider {
                 provider,
                 model,
                 account,
-                None,
-                Box::new(move |_, _, _| {
+                Box::new(move |_, _| {
                     Box::pin(async move {
                         let events = futures::stream::once(async move {
                             Err::<ProviderEvent, _>(
diff --git a/backend/crates/gateway-core/tests/engine/middleware/cold.rs b/backend/crates/gateway-core/tests/engine/middleware/cold.rs
index 3015d470d..93bb8087b 100644
--- a/backend/crates/gateway-core/tests/engine/middleware/cold.rs
+++ b/backend/crates/gateway-core/tests/engine/middleware/cold.rs
@@ -88,7 +88,7 @@ fn plan(action: Action) -> FrozenMiddlewarePlan {
 }
 
 fn terminal(polls: Arc<AtomicUsize>, released: Arc<AtomicUsize>) -> ProviderMiddlewareTerminal {
-    Box::new(move |_, _, _| {
+    Box::new(move |_, _| {
         Box::pin(async move {
             let metadata = ProviderCallMetadata::new(
                 ProviderKind::new("openai").unwrap(),
@@ -127,7 +127,6 @@ fn inspecting_a_response_waits_for_the_outer_stream_and_keeps_send_facts() {
                 context(),
                 operation(),
                 ClientTransport::HttpJson,
-                None,
                 terminal(polls.clone(), released.clone()),
             )
             .await
@@ -166,7 +165,6 @@ fn rejecting_metadata_drops_the_unactivated_handler_and_account_lease() {
             context(),
             operation(),
             ClientTransport::HttpJson,
-            None,
             terminal(polls.clone(), released.clone()),
         )
         .await
@@ -196,8 +194,7 @@ fn middleware_rejection_before_next_does_not_wait_for_activation() {
                 context(),
                 operation(),
                 ClientTransport::HttpJson,
-                None,
-                Box::new(|_, _, _| panic!("rejected middleware cannot prepare upstream")),
+                Box::new(|_, _| panic!("rejected middleware cannot prepare upstream")),
             )
             .await
             .err()
diff --git a/backend/crates/gateway-core/tests/engine/middleware/mod.rs b/backend/crates/gateway-core/tests/engine/middleware/mod.rs
index b86b834fb..492b6c370 100644
--- a/backend/crates/gateway-core/tests/engine/middleware/mod.rs
+++ b/backend/crates/gateway-core/tests/engine/middleware/mod.rs
@@ -340,7 +340,7 @@ fn attempt_middleware_consumes_owned_next_once_and_preserves_host_envelopes() {
 
         let terminal: ProviderMiddlewareTerminal = {
             let terminal_calls = Arc::clone(&terminal_calls);
-            Box::new(move |operation, headers, _| {
+            Box::new(move |operation, headers| {
                 terminal_calls.fetch_add(1, Ordering::SeqCst);
                 Box::pin(async move {
                     assert!(headers.is_empty());
@@ -392,7 +392,6 @@ fn attempt_middleware_consumes_owned_next_once_and_preserves_host_envelopes() {
             context(),
             operation(),
             ClientTransport::HttpJson,
-            None,
             terminal,
         )
         .await
@@ -487,7 +486,7 @@ fn attempt_passthrough_preserves_parsed_wire_for_every_client_transport() {
                 payload.clone(),
             )
             .unwrap();
-            let terminal: ProviderMiddlewareTerminal = Box::new(move |_, _, _| {
+            let terminal: ProviderMiddlewareTerminal = Box::new(move |_, _| {
                 Box::pin(async move {
                     Ok(ProviderStream::new(
                         empty_provider_stream().metadata().clone(),
@@ -501,7 +500,6 @@ fn attempt_passthrough_preserves_parsed_wire_for_every_client_transport() {
                 context(),
                 operation(),
                 transport,
-                None,
                 terminal,
             )
             .await
@@ -569,7 +567,7 @@ fn attempt_sse_encoding_keeps_opaque_metadata_from_creating_extra_frames() {
                 Some(10),
             )
             .unwrap();
-            let terminal: ProviderMiddlewareTerminal = Box::new(move |_, _, _| {
+            let terminal: ProviderMiddlewareTerminal = Box::new(move |_, _| {
                 Box::pin(async move {
                     Ok(ProviderStream::new(
                         empty_provider_stream().metadata().clone(),
@@ -584,7 +582,6 @@ fn attempt_sse_encoding_keeps_opaque_metadata_from_creating_extra_frames() {
                 context(),
                 operation(),
                 ClientTransport::HttpSse,
-                None,
                 terminal,
             )
             .await
@@ -599,7 +596,7 @@ fn attempt_middleware_preserves_multi_value_and_authentication_headers() {
         let allowed_calls = Arc::new(AtomicUsize::new(0));
         let allowed_terminal: ProviderMiddlewareTerminal = {
             let allowed_calls = Arc::clone(&allowed_calls);
-            Box::new(move |_operation, headers, _| {
+            Box::new(move |_operation, headers| {
                 allowed_calls.fetch_add(1, Ordering::SeqCst);
                 Box::pin(async move {
                     assert_eq!(headers.len(), 2);
@@ -627,7 +624,6 @@ fn attempt_middleware_preserves_multi_value_and_authentication_headers() {
             context(),
             operation(),
             ClientTransport::HttpJson,
-            None,
             allowed_terminal,
         )
         .await
@@ -637,7 +633,7 @@ fn attempt_middleware_preserves_multi_value_and_authentication_headers() {
         let calls = Arc::new(AtomicUsize::new(0));
         let terminal: ProviderMiddlewareTerminal = {
             let calls = calls.clone();
-            Box::new(move |_, headers, _| {
+            Box::new(move |_, headers| {
                 calls.fetch_add(1, Ordering::SeqCst);
                 Box::pin(async move {
                     assert_eq!(headers[0].name(), "authorization");
@@ -661,7 +657,6 @@ fn attempt_middleware_preserves_multi_value_and_authentication_headers() {
             context(),
             operation(),
             ClientTransport::HttpJson,
-            None,
             terminal,
         )
         .await
@@ -741,8 +736,7 @@ fn attempt_middleware_cannot_add_image_generation_to_a_denied_scope() {
             ProviderKind::new("openai").unwrap(),
             Some("gpt-test".into()),
             ProviderAccountId::new("acct_middleware").unwrap(),
-            None,
-            Box::new(move |operation, _, _| {
+            Box::new(move |operation, _| {
                 Box::pin(async move {
                     assert!(operation.image_generation_requested());
                     count.fetch_add(1, Ordering::SeqCst);
diff --git a/backend/crates/gateway-plugin/runtime/src/adapter/middleware/request.rs b/backend/crates/gateway-plugin/runtime/src/adapter/middleware/request.rs
index 58af1b191..82cc532ad 100644
--- a/backend/crates/gateway-plugin/runtime/src/adapter/middleware/request.rs
+++ b/backend/crates/gateway-plugin/runtime/src/adapter/middleware/request.rs
@@ -98,7 +98,6 @@ pub(super) async fn invoke(
         scope,
     )?;
     let head = MiddlewareRequestHead {
-        provider_parameters: invocation.provider_parameters(),
         settings_sources: invocation.settings_sources(),
         settings: invocation
             .settings()
diff --git a/backend/crates/gateway-plugin/runtime/src/callback/middleware/mod.rs b/backend/crates/gateway-plugin/runtime/src/callback/middleware/mod.rs
index a2b37e43b..d3792438d 100644
--- a/backend/crates/gateway-plugin/runtime/src/callback/middleware/mod.rs
+++ b/backend/crates/gateway-plugin/runtime/src/callback/middleware/mod.rs
@@ -135,15 +135,6 @@ pub(crate) enum MiddlewareCompletionBody {
 }
 
 impl MiddlewareInvocation {
-    pub(crate) fn provider_parameters(&self) -> Option<serde_json::Map<String, serde_json::Value>> {
-        self.state
-            .lock()
-            .unwrap_or_else(std::sync::PoisonError::into_inner)
-            .original_request
-            .provider_parameters()
-            .cloned()
-    }
-
     pub(crate) fn settings(&self) -> Result<serde_json::Value, PluginFault> {
         let state = self
             .state
@@ -343,12 +334,6 @@ impl MiddlewareInvocation {
         request: MiddlewareNextRequest,
         payload: Vec<u8>,
     ) -> Result<MiddlewareRequest, PluginFault> {
-        if let Some(parameters) = request.provider_parameters {
-            if original.provider_parameters().is_none() {
-                return Err(invalid());
-            }
-            original = original.with_provider_parameters(parameters);
-        }
         if let Some(settings) = request.settings {
             let current = original.settings().ok_or_else(|| {
                 PluginFault::new(
diff --git a/backend/crates/gateway-plugin/runtime/tests/generation/policy/facts/mod.rs b/backend/crates/gateway-plugin/runtime/tests/generation/policy/facts/mod.rs
index 3db3774c1..5c9366196 100644
--- a/backend/crates/gateway-plugin/runtime/tests/generation/policy/facts/mod.rs
+++ b/backend/crates/gateway-plugin/runtime/tests/generation/policy/facts/mod.rs
@@ -71,8 +71,7 @@ async fn reading_websocket_facts_preserves_original_text_and_opaque_messages() {
         attempt_middleware_context_for_transport(Arc::default(), ClientTransport::WebSocket),
         operation(),
         ClientTransport::WebSocket,
-        None,
-        Box::new(move |_, _, _| {
+        Box::new(move |_, _| {
             Box::pin(async move {
                 Ok(ProviderStream::new(
                     ProviderCallMetadata::new(
@@ -228,8 +227,7 @@ async fn facts_are_readable_without_replacing_or_duplicating_the_original_execut
         attempt_middleware_context(Arc::default()),
         operation(),
         ClientTransport::HttpJson,
-        None,
-        Box::new(move |_, _, _| {
+        Box::new(move |_, _| {
             Box::pin(async move {
                 Ok(ProviderStream::new(
                     metadata,
diff --git a/backend/crates/gateway-plugin/runtime/tests/generation/policy/lifecycle.rs b/backend/crates/gateway-plugin/runtime/tests/generation/policy/lifecycle.rs
index 37f8e3a31..c8f49d63f 100644
--- a/backend/crates/gateway-plugin/runtime/tests/generation/policy/lifecycle.rs
+++ b/backend/crates/gateway-plugin/runtime/tests/generation/policy/lifecycle.rs
@@ -3,72 +3,6 @@
 use super::*;
 use gateway_admin::ports::plugins::PluginPreparation;
 
-#[tokio::test]
-async fn provider_parameters_compose_through_sdk_without_merging_deleted_fields() {
-    let worker = std::fs::read(env!("CARGO_BIN_EXE_gateway-plugin-test-middleware")).unwrap();
-    let package = crate::support::package_with_contributions(
-        &worker,
-        Contributions::from([crate::support::contribution(
-            Capability::Middleware,
-            vec![Stage::Attempt],
-            vec!["openai".into()],
-            vec!["openai".into()],
-        )]),
-    );
-    let original = serde_json::json!({"installation_id":"account-default", "future":{"keep":true}});
-    let first = serde_json::json!({"installation_id":"plugin-first"});
-    let last = serde_json::json!({});
-    let instances = [
-        ("parameters-first", original.clone(), first.clone()),
-        ("parameters-last", first, serde_json::Value::Null),
-    ]
-    .into_iter()
-    .enumerate()
-    .map(|(index, (id, expected, parameters))| InstanceFixture {
-        id,
-        configuration: serde_json::json!({"mode":"parameters", "attempt":true,
-            "expected_parameters":expected, "parameters":parameters}),
-        bindings: vec![binding(
-            MIDDLEWARE_CONTRIBUTION,
-            "attempt",
-            index as i32,
-            PluginFailurePolicy::Reject,
-        )],
-    })
-    .collect();
-    let (cache, runtime) = setup_package(instances, package).await;
-    let generation = prepare(&runtime).await;
-    let plan = runtime
-        .execution_registry()
-        .middleware(&generation)
-        .unwrap();
-    let downstream = Downstream {
-        calls: Arc::default(),
-        closes: Arc::default(),
-        reads: Arc::default(),
-        error: false,
-    };
-    let response = plan
-        .handle(
-            attempt_middleware_context(Arc::default()),
-            budget_request().with_provider_parameters(original.as_object().unwrap().clone()),
-            gateway_core::middleware::compose(Vec::new(), move |request| {
-                assert_eq!(
-                    request.provider_parameters().unwrap(),
-                    last.as_object().unwrap()
-                );
-                downstream.into_next().run(request)
-            }),
-        )
-        .await
-        .unwrap();
-    let (_, _, _, body, _) = response.into_parts();
-    body.close().await;
-    drop(plan);
-    drop(generation);
-    super::super::wait_until_empty(cache.path()).await;
-}
-
 #[tokio::test]
 async fn partial_update_preserves_inflight_middleware_and_uses_new_configuration_for_new_calls() {
     let (cache, store, runtime) = super::super::setup_with_contributions(Contributions::from([
diff --git a/backend/crates/gateway-plugin/runtime/tests/support/middleware/mod.rs b/backend/crates/gateway-plugin/runtime/tests/support/middleware/mod.rs
index 8d3f74dee..e035a7896 100644
--- a/backend/crates/gateway-plugin/runtime/tests/support/middleware/mod.rs
+++ b/backend/crates/gateway-plugin/runtime/tests/support/middleware/mod.rs
@@ -545,19 +545,6 @@ async fn main() -> Result<(), Box<dyn std::error::Error>> {
                     call.request.head.settings = settings.clone();
                 }
             }
-            if mode == "parameters" {
-                assert_eq!(
-                    serde_json::to_value(&call.request.head.provider_parameters).unwrap(),
-                    configuration["expected_parameters"],
-                );
-                if let Some(parameters) = configuration.get("parameters") {
-                    call.request.head.provider_parameters = if parameters.is_null() {
-                        None
-                    } else {
-                        Some(parameters.as_object().unwrap().clone())
-                    };
-                }
-            }
             if mode == "inspect" && !call.request.body.is_empty() {
                 // 读取和解析只能作用于副本，不能把解析结果写回未改写的正文
                 assert!(serde_json::from_slice::<serde_json::Value>(&call.request.body).is_ok());
diff --git a/backend/crates/gateway-plugin/runtime/tests/support/worker/mod.rs b/backend/crates/gateway-plugin/runtime/tests/support/worker/mod.rs
index bad73a66f..a1607c334 100644
--- a/backend/crates/gateway-plugin/runtime/tests/support/worker/mod.rs
+++ b/backend/crates/gateway-plugin/runtime/tests/support/worker/mod.rs
@@ -1046,7 +1046,6 @@ impl Peer {
                         id,
                         NEXT_METHOD,
                         serde_json::to_value(MiddlewareNextRequest {
-                            provider_parameters: None,
                             settings: None,
                             protocol: None,
                             header_mutations: Vec::new(),
diff --git a/backend/crates/gateway-plugin/sdk/docs/capabilities.md b/backend/crates/gateway-plugin/sdk/docs/capabilities.md
index 461517aea..0a518c9bc 100644
--- a/backend/crates/gateway-plugin/sdk/docs/capabilities.md
+++ b/backend/crates/gateway-plugin/sdk/docs/capabilities.md
@@ -402,7 +402,12 @@ Ping 的自动 Pong 与关闭握手属于底层 WebSocket 协议事实；插件
 所有外层处理结束后，Provider 才把结果交给 transport 发送。插件错误、非法传输值或正文超限在原生发送前结束，
 不自动跳过、重放或切换传输；取消、请求截止与回调资源沿用当前 attempt
 
+身份策略可在 `request` / `attempt` 读取原始输入，以真实 Key 与账号标识调用私有状态服务维护映射，
+再在 `outbound` 自行改写完整请求中的身份及关联字段。UUID 生成、并发创建、持久化、会话与缓存标识派生均由插件负责；
+通用中间件层不解释 installation ID、device ID 等策略字段，也不在插件输出后重新派生业务字段
+
 WebSocket 的 `body` 是准备发送的一条完整 UTF-8 文本消息，`headers` 和 `uri` 是候选 opening。
+新响应链按出站改写产生的 URI / 握手头差异分区，精确续接仍使用持有原响应链的连接。
 复用连接时不能改写已发生的握手；宿主不为插件主动重连、重放消息或重建续接。
 插件需要握手身份与消息内容一致时，应结合实际连接与续接语义选择改写
 
@@ -429,17 +434,6 @@ request 与 attempt 阶段通过 `append_header` 添加的请求头会进入上
 OpenAI 与 xAI 的上游 headers 先由账号和画像生成，插件同名字段覆盖基线，同名多值按插件顺序保留；不存在按认证、Cookie 或会话名称划分的保护列表。
 实际账号租约、凭据版本与计费归属仍记录真实选中事实，不随插件修改 header 名称而伪造
 
-attempt 的 `request.head.provider_parameters` 携带 Provider 提供的本次构造参数；没有该能力的执行不提供此对象。
-OpenAI 原生 Responses、Images、Search 与 Live 创建请求提供 `installation_id` 字符串，默认取自选中账号，
-用于原生安装身份、已有 turn metadata 身份字段及会话、缓存关联标识的派生。独立 `upstream_adapter` 自行构造其请求。
-
-插件直接修改此对象，SDK 在值改变时提交完整替换；空对象明确删除全部参数，将原本存在的对象设为 `None` 同样提交空对象。
-线协议的 `next.provider_parameters` 省略时保留原值，显式 `null` 或非对象类型拒绝。
-后续插件读取前层结果，Core / Runtime 不解释业务字段、不深合并；缺失必需字段或类型错误在发送前失败且禁止重试，不补回账号默认身份。
-
-身份选择、Key 与账号配对、UUID 生成与持久化由插件负责，可复用已有状态服务；参数不写回账号凭据、全局设置或真实计费事实。
-WS 新响应链按构造身份区分连接，精确续接仍使用实际持有该响应链的原连接；Live sideband / hangup 不继承创建请求的临时参数
-
 request 阶段 `request.head.settings` 是本次调用的有效设置对象，包含 `runtime`、`fast_mode`、`client_limits` 和 `timeout_ms`。
 `fast_mode` 使用 `default`、`enabled`、`disabled` 三态，具体档位语义见[账号分组](../../../../../docs/api.md#6-账号分组)。
 `runtime` 使用宿主快照的设置字段，画像已合并 Client Key 设置；可以修改映射、画像、调度、位置及计价等执行参数。
diff --git a/backend/crates/gateway-plugin/sdk/src/call/middleware/mod.rs b/backend/crates/gateway-plugin/sdk/src/call/middleware/mod.rs
index 35ed53ff5..21c071385 100644
--- a/backend/crates/gateway-plugin/sdk/src/call/middleware/mod.rs
+++ b/backend/crates/gateway-plugin/sdk/src/call/middleware/mod.rs
@@ -70,9 +70,6 @@ pub struct MiddlewareRequestHead {
     /// 当前请求的完整有效执行设置；尚未建立可改写设置的边界使用 null
     #[serde(default)]
     pub settings: serde_json::Value,
-    /// 本次 Provider 构造参数；仅原生 attempt 提供
-    #[serde(default, skip_serializing_if = "Option::is_none")]
-    pub provider_parameters: Option<serde_json::Map<String, serde_json::Value>>,
     pub request_id: String,
     pub client_key_id: String,
     pub account_group_ids: Vec<String>,
@@ -131,13 +128,6 @@ pub struct MiddlewareNextRequest {
         deserialize_with = "deserialize_replacement"
     )]
     pub settings: Option<serde_json::Value>,
-    /// 完整替换构造参数；空对象仍表示显式替换，不隐式合并或补回删除字段
-    #[serde(
-        default,
-        skip_serializing_if = "Option::is_none",
-        deserialize_with = "deserialize_replacement"
-    )]
-    pub provider_parameters: Option<serde_json::Map<String, serde_json::Value>>,
     #[serde(default, skip_serializing_if = "Option::is_none")]
     pub protocol: Option<String>,
     #[serde(default)]
diff --git a/backend/crates/gateway-plugin/sdk/src/client/middleware/mod.rs b/backend/crates/gateway-plugin/sdk/src/client/middleware/mod.rs
index 4c340642a..79bd6ba8d 100644
--- a/backend/crates/gateway-plugin/sdk/src/client/middleware/mod.rs
+++ b/backend/crates/gateway-plugin/sdk/src/client/middleware/mod.rs
@@ -39,7 +39,6 @@ pub struct MiddlewareRequest {
     pub body: Vec<u8>,
     original_protocol: String,
     original_settings: serde_json::Value,
-    original_provider_parameters: Option<serde_json::Map<String, serde_json::Value>>,
     original_headers: Vec<MiddlewareHeader>,
     original_body: Vec<u8>,
     body_replaced: bool,
@@ -99,9 +98,6 @@ impl MiddlewareRequest {
         };
         (
             MiddlewareNextRequest {
-                provider_parameters: (self.head.provider_parameters
-                    != self.original_provider_parameters)
-                    .then(|| self.head.provider_parameters.unwrap_or_default()),
                 settings: (self.head.settings != self.original_settings)
                     .then_some(self.head.settings),
                 protocol,
@@ -345,7 +341,6 @@ impl RequestCall {
             context: call.context,
             request: MiddlewareRequest {
                 original_settings: head.settings.clone(),
-                original_provider_parameters: head.provider_parameters.clone(),
                 body: call.payload,
                 original_body,
                 body_replaced: false,
diff --git a/backend/crates/gateway-plugin/sdk/tests/call/middleware/mod.rs b/backend/crates/gateway-plugin/sdk/tests/call/middleware/mod.rs
index 8401274c0..65a1c73a6 100644
--- a/backend/crates/gateway-plugin/sdk/tests/call/middleware/mod.rs
+++ b/backend/crates/gateway-plugin/sdk/tests/call/middleware/mod.rs
@@ -13,37 +13,6 @@ use gateway_plugin_sdk::{
 };
 use serde_json::json;
 
-#[test]
-fn provider_parameters_distinguish_preserve_empty_and_invalid_replacement() {
-    let preserved: MiddlewareNextRequest =
-        serde_json::from_value(json!({"body":"preserve"})).unwrap();
-    assert!(preserved.provider_parameters.is_none());
-    for replacement in [json!({}), json!({"installation_id":null})] {
-        let request: MiddlewareNextRequest = serde_json::from_value(json!({
-            "body":"preserve", "provider_parameters":replacement,
-        }))
-        .unwrap();
-        assert_eq!(
-            request.provider_parameters.as_ref(),
-            replacement.as_object()
-        );
-    }
-    for invalid in [
-        json!(null),
-        json!([]),
-        json!("invalid"),
-        json!(42),
-        json!(false),
-    ] {
-        assert!(
-            serde_json::from_value::<MiddlewareNextRequest>(json!({
-                "body":"preserve", "provider_parameters":invalid,
-            }))
-            .is_err()
-        );
-    }
-}
-
 #[test]
 fn settings_replacement_preserves_explicit_null_for_host_validation() {
     let preserved: MiddlewareNextRequest =
@@ -75,7 +44,6 @@ fn middleware_capability_and_mounts_have_one_stable_wire_vocabulary() {
 #[test]
 fn middleware_request_keeps_body_out_of_json_and_rejects_unknown_fields() {
     let request = MiddlewareRequestHead {
-        provider_parameters: None,
         settings_sources: serde_json::Value::Null,
         settings: serde_json::Value::Null,
         client_key_id: "fixture-key".into(),
@@ -113,7 +81,6 @@ fn middleware_request_keeps_body_out_of_json_and_rejects_unknown_fields() {
 #[test]
 fn next_distinguishes_preserve_from_replace_empty_and_uses_incremental_headers() {
     let preserve = MiddlewareNextRequest {
-        provider_parameters: None,
         settings: None,
         protocol: None,
         header_mutations: Vec::new(),
@@ -126,7 +93,6 @@ fn next_distinguishes_preserve_from_replace_empty_and_uses_incremental_headers()
     );
 
     let replace = MiddlewareNextRequest {
-        provider_parameters: None,
         settings: None,
         protocol: Some("xai".into()),
         header_mutations: vec![
diff --git a/backend/crates/gateway-plugin/sdk/tests/client/session/mod.rs b/backend/crates/gateway-plugin/sdk/tests/client/session/mod.rs
index 0ebef12d4..f0292a39f 100644
--- a/backend/crates/gateway-plugin/sdk/tests/client/session/mod.rs
+++ b/backend/crates/gateway-plugin/sdk/tests/client/session/mod.rs
@@ -391,7 +391,6 @@ fn middleware_context(id: u64) -> CallContext {
 
 pub(super) fn middleware_request() -> MiddlewareRequestHead {
     MiddlewareRequestHead {
-        provider_parameters: None,
         settings_sources: serde_json::Value::Null,
         settings: serde_json::Value::Null,
         client_key_id: "fixture-key".into(),
diff --git a/backend/crates/providers/openai/src/provider/execution.rs b/backend/crates/providers/openai/src/provider/execution.rs
index a87bb15ba..07e21dc3b 100644
--- a/backend/crates/providers/openai/src/provider/execution.rs
+++ b/backend/crates/providers/openai/src/provider/execution.rs
@@ -179,8 +179,7 @@ impl CodexProvider {
                 provider_kind,
                 requested_model.map(|model| model.as_str().to_owned()),
                 account_id,
-                Some(RequestParameters::baseline(lease.installation_id())),
-                Box::new(move |operation, middleware_headers, parameters| {
+                Box::new(move |operation, middleware_headers| {
                     Box::pin(async move {
                         provider
                             .execute_selected_raw_json_endpoint(
@@ -188,11 +187,8 @@ impl CodexProvider {
                                 operation,
                                 middleware_headers,
                                 request,
-                                SelectedRequest {
-                                    parameters: RequestParameters::decode(parameters)?,
-                                    lease,
-                                    account_selection_wait_ms,
-                                },
+                                lease,
+                                account_selection_wait_ms,
                             )
                             .await
                     })
@@ -207,13 +203,9 @@ impl CodexProvider {
         operation: Operation,
         middleware_headers: Vec<MiddlewareHeader>,
         mut request: RawJsonEndpointRequest,
-        selected: SelectedRequest,
+        mut lease: CodexCredentialLease,
+        account_selection_wait_ms: u64,
     ) -> Result<ProviderStream, ProviderError> {
-        let SelectedRequest {
-            parameters,
-            mut lease,
-            account_selection_wait_ms,
-        } = selected;
         let affinity = match &operation {
             Operation::GenerateImage(image) => {
                 let model = endpoint_requested_model(image.payload());
@@ -337,7 +329,7 @@ impl CodexProvider {
             lease.capacity_snapshot(),
         ));
         // Standalone Provider 端点没有可证明的账号 owner；Images/Search metadata 必须按
-        // 跨账号输入收敛到本次构造参数，不能沿用下游声明的账号身份
+        // 跨账号输入收敛到当前 lease，不能沿用下游声明的账号或 installation identity
         let turn_metadata = payload
             .context()
             .get("turn_metadata")
@@ -345,12 +337,11 @@ impl CodexProvider {
             .and_then(|metadata| {
                 crate::transport::request::scope_turn_metadata(
                     metadata,
-                    &parameters.installation_id,
+                    lease.installation_id(),
                     true,
                 )
             });
         let events = cold_json_response_stream(ColdJsonResponse {
-            parameters,
             client: self
                 .client_for_request(&context)?
                 .for_account(lease.account())
@@ -392,7 +383,6 @@ struct RawJsonEndpointRequest {
 }
 
 pub(super) struct ColdResponse {
-    pub(super) parameters: RequestParameters,
     pub(super) client: CodexBackendClient,
     pub(super) response_origin: Url,
     pub(super) request: CodexResponsesRequest,
@@ -412,7 +402,6 @@ pub(super) struct ColdResponse {
 }
 
 pub(super) struct ColdJsonResponse {
-    pub(super) parameters: RequestParameters,
     pub(super) client: CodexBackendClient,
     pub(super) response_origin: Url,
     pub(super) endpoint_path: &'static str,
@@ -657,7 +646,7 @@ pub(super) fn cold_json_response_stream(request: ColdJsonResponse) -> EventStrea
         let response = create_json_attempt(
             &request,
             &active_account,
-            &request.parameters.installation_id,
+            request.lease.installation_id(),
             &authorization,
             cookie_header.as_ref(),
             account_selection,
@@ -776,7 +765,6 @@ fn image_response_metering(
 
 pub(super) fn cold_response_stream(response: ColdResponse) -> EventStream {
     let ColdResponse {
-        parameters,
         client,
         response_origin,
         request,
@@ -833,7 +821,7 @@ pub(super) fn cold_response_stream(response: ColdResponse) -> EventStream {
                 &request,
                 &request_id,
                 &active_account,
-                &parameters.installation_id,
+                lease.installation_id(),
                 &authorization,
                 cookie_header.as_ref(),
                 account_selection,
diff --git a/backend/crates/providers/openai/src/provider/live.rs b/backend/crates/providers/openai/src/provider/live.rs
index 8a13454ee..94a032e6d 100644
--- a/backend/crates/providers/openai/src/provider/live.rs
+++ b/backend/crates/providers/openai/src/provider/live.rs
@@ -280,8 +280,7 @@ impl CodexProvider {
                 provider_kind,
                 Some(upstream_model.as_str().to_owned()),
                 account_id,
-                Some(RequestParameters::baseline(lease.installation_id())),
-                Box::new(move |operation, middleware_headers, parameters| {
+                Box::new(move |operation, middleware_headers| {
                     Box::pin(async move {
                         provider
                             .execute_selected_live_call(
@@ -289,11 +288,8 @@ impl CodexProvider {
                                 operation,
                                 upstream_model,
                                 middleware_headers,
-                                SelectedRequest {
-                                    parameters: RequestParameters::decode(parameters)?,
-                                    lease,
-                                    account_selection_wait_ms,
-                                },
+                                lease,
+                                account_selection_wait_ms,
                             )
                             .await
                     })
@@ -308,13 +304,9 @@ impl CodexProvider {
         operation: Operation,
         upstream_model: UpstreamModelId,
         middleware_headers: Vec<MiddlewareHeader>,
-        selected: SelectedRequest,
+        mut lease: CodexCredentialLease,
+        account_selection_wait_ms: u64,
     ) -> Result<ProviderStream, ProviderError> {
-        let SelectedRequest {
-            parameters,
-            mut lease,
-            account_selection_wait_ms,
-        } = selected;
         let Operation::ProviderHttp(request) = operation else {
             return Err(provider_error(
                 ProviderErrorKind::InvalidRequest,
@@ -374,7 +366,6 @@ impl CodexProvider {
             .cloned()
             .collect::<Vec<_>>();
         let events = cold_live_call_stream(ColdLiveCall {
-            parameters,
             client: self
                 .client_for_request(&context)?
                 .for_account(lease.account())
@@ -407,7 +398,6 @@ impl CodexProvider {
 }
 
 struct ColdLiveCall {
-    parameters: RequestParameters,
     client: CodexBackendClient,
     registry: Arc<CodexLiveRegistry>,
     response_origin: Url,
@@ -451,7 +441,7 @@ fn cold_live_call_stream(request: ColdLiveCall) -> EventStream {
             authorization.expose_secret(),
             active_account.upstream_account_id(),
             &request_id,
-            Some(&request.parameters.installation_id),
+            Some(request.lease.installation_id()),
         );
         request_context.trace = Some(&trace);
         request_context.account_selection = CodexAccountSelectionTelemetry::new(
diff --git a/backend/crates/providers/openai/src/provider/mod.rs b/backend/crates/providers/openai/src/provider/mod.rs
index 03fb72e27..5ca2730a0 100644
--- a/backend/crates/providers/openai/src/provider/mod.rs
+++ b/backend/crates/providers/openai/src/provider/mod.rs
@@ -107,7 +107,6 @@ mod execution;
 mod failure;
 mod live;
 mod observation;
-mod parameters;
 mod upstream_adapter;
 mod workers;
 pub(crate) use live::{CodexLiveGateway, CodexLiveRegistry};
@@ -118,7 +117,6 @@ use execution::*;
 pub use failure::openai_failure_affects_account_score;
 use failure::*;
 use observation::*;
-use parameters::RequestParameters;
 pub(crate) use workers::worker_contributions;
 
 const PROVIDER_NAME: &str = "openai";
@@ -221,14 +219,9 @@ impl PreparedGenerateRequest {
 }
 
 struct SelectedGenerate {
-    request: SelectedRequest,
-    frozen_requirements: CapabilityRequirements,
-}
-
-struct SelectedRequest {
     lease: CodexCredentialLease,
     account_selection_wait_ms: u64,
-    parameters: RequestParameters,
+    frozen_requirements: CapabilityRequirements,
 }
 
 impl CodexProvider {
@@ -756,10 +749,7 @@ impl Provider for CodexProvider {
                 provider_kind,
                 Some(upstream_model.as_str().to_owned()),
                 account_id,
-                adapter
-                    .is_none()
-                    .then(|| RequestParameters::baseline(lease.installation_id())),
-                Box::new(move |operation, middleware_headers, parameters| {
+                Box::new(move |operation, middleware_headers| {
                     Box::pin(async move {
                         if let Some(adapter) = adapter {
                             return provider.execute_upstream_adapter(
@@ -780,11 +770,8 @@ impl Provider for CodexProvider {
                                 terminal_model,
                                 terminal_context,
                                 SelectedGenerate {
-                                    request: SelectedRequest {
-                                        parameters: RequestParameters::decode(parameters)?,
-                                        lease,
-                                        account_selection_wait_ms,
-                                    },
+                                    lease,
+                                    account_selection_wait_ms,
                                     frozen_requirements,
                                 },
                             )
@@ -806,12 +793,8 @@ impl CodexProvider {
         selected: SelectedGenerate,
     ) -> Result<ProviderStream, ProviderError> {
         let SelectedGenerate {
-            request:
-                SelectedRequest {
-                    parameters,
-                    mut lease,
-                    account_selection_wait_ms,
-                },
+            mut lease,
+            account_selection_wait_ms,
             frozen_requirements,
         } = selected;
         let Operation::Generate(generate) = operation else {
@@ -951,7 +934,7 @@ impl CodexProvider {
             .then(|| crate::transport::diagnostics::evidence::request_state(&upstream_request));
         scope_request_to_account(
             &mut upstream_request,
-            &parameters.installation_id,
+            lease.installation_id(),
             account_scope,
         );
         if let Some(before) = state_before {
@@ -1106,7 +1089,6 @@ impl CodexProvider {
             AttemptTransport::Default | AttemptTransport::Fallback => 0,
         };
         let events = cold_response_stream(ColdResponse {
-            parameters,
             client: self
                 .client_for_request(&context)?
                 .for_account(lease.account())
diff --git a/backend/crates/providers/openai/src/provider/parameters.rs b/backend/crates/providers/openai/src/provider/parameters.rs
deleted file mode 100644
index ac0e3d95a..000000000
--- a/backend/crates/providers/openai/src/provider/parameters.rs
+++ /dev/null
@@ -1,35 +0,0 @@
-//! OpenAI 原生请求的构造参数；只解释本次值，不维护插件身份策略
-
-use gateway_core::{
-    error::{ProviderError, ProviderErrorKind},
-    upstream::UpstreamSendState,
-};
-use serde::Deserialize;
-use serde_json::{Map, Value};
-
-#[derive(Deserialize)]
-pub(super) struct RequestParameters {
-    pub(super) installation_id: String,
-}
-
-impl RequestParameters {
-    pub(super) fn baseline(installation_id: &str) -> Map<String, Value> {
-        Map::from_iter([(
-            "installation_id".into(),
-            Value::String(installation_id.to_owned()),
-        )])
-    }
-
-    pub(super) fn decode(parameters: Option<Map<String, Value>>) -> Result<Self, ProviderError> {
-        let invalid = || {
-            ProviderError::new(
-                ProviderErrorKind::InvalidRequest,
-                UpstreamSendState::NotSent,
-            )
-            .with_retry_prohibited()
-        };
-        // 参数基线已在选号后提供，显式删除和类型错误不能回退为账号默认身份
-        serde_json::from_value(Value::Object(parameters.ok_or_else(invalid)?))
-            .map_err(|_| invalid())
-    }
-}
diff --git a/backend/crates/providers/openai/src/transport/client_sse.rs b/backend/crates/providers/openai/src/transport/client_sse.rs
index e1f778ff8..24f437014 100644
--- a/backend/crates/providers/openai/src/transport/client_sse.rs
+++ b/backend/crates/providers/openai/src/transport/client_sse.rs
@@ -622,10 +622,7 @@ impl CodexBackendClient {
         let mut key = CodexWebSocketPoolKey::new(&self.base_url, account_id, conversation_id)
             .with_egress_key(&self.egress_key)
             .with_outbound_proxy(self.outbound_proxy.as_ref())
-            .with_connection_profile(format!(
-                "{connection_profile}\0{}",
-                context.installation_id.unwrap_or_default(),
-            ));
+            .with_connection_profile(connection_profile);
         if let Some(connection_id) = request.downstream_websocket_connection_id.as_deref() {
             key = key.with_downstream_connection_id(connection_id);
         }
diff --git a/backend/crates/providers/openai/tests/provider/contract/correlation.rs b/backend/crates/providers/openai/tests/provider/contract/correlation.rs
index f3c0d1986..58889c1e5 100644
--- a/backend/crates/providers/openai/tests/provider/contract/correlation.rs
+++ b/backend/crates/providers/openai/tests/provider/contract/correlation.rs
@@ -2,337 +2,6 @@
 
 use super::*;
 
-#[derive(Debug)]
-struct ParametersMiddleware(Map<String, Value>);
-
-impl MiddlewarePlan for ParametersMiddleware {
-    fn handle(
-        &self,
-        context: MiddlewareContext,
-        request: MiddlewareRequest,
-        next: MiddlewareNext,
-    ) -> BoxFuture<'static, Result<MiddlewareResponse, MiddlewareError>> {
-        assert_eq!(context.mount(), MiddlewareMount::Attempt);
-        assert!(request.provider_parameters().unwrap()["installation_id"].is_string());
-        next.run(request.with_provider_parameters(self.0.clone()))
-    }
-}
-
-#[tokio::test]
-async fn request_parameters_drive_native_identity_and_derivation_across_http_and_websocket() {
-    let store = Arc::new(MemoryAccountStore::default());
-    create_account(&store, "acct_provider_contract").await;
-    let identities = [
-        "f77b9b8e-563a-4d84-a66f-f2a0c98d5a8e",
-        "f6e974b5-708d-4940-b619-1ab2c58c2f2c",
-    ];
-    let mut captures = Vec::new();
-    for identity in identities {
-        for websocket in [false, true] {
-            let (base_url, capture): (
-                String,
-                BoxFuture<'static, (reqwest::header::HeaderMap, Value)>,
-            ) = if websocket {
-                let listener = TcpListener::bind("127.0.0.1:0").await.unwrap();
-                let url = format!("http://{}", listener.local_addr().unwrap());
-                let task = tokio::spawn(async move {
-                    let (socket, _) = listener.accept().await.unwrap();
-                    let mut headers = None;
-                    let mut socket =
-                        crate::transport::accept_codex_test_websocket_with(socket, |request, _| {
-                            headers = Some(request.headers().clone())
-                        })
-                        .await;
-                    let frame = socket.next().await.unwrap().unwrap();
-                    let body = serde_json::from_str(frame.to_text().unwrap()).unwrap();
-                    socket.send(Message::Text(json!({"type":"response.completed", "response":{
-                            "id":"resp_parameters", "model":"gpt-5.4", "status":"completed", "output":[]
-                        }}).to_string().into())).await.unwrap();
-                    (headers.unwrap(), body)
-                });
-                (url, Box::pin(async { task.await.unwrap() }))
-            } else {
-                let server = MockServer::start().await;
-                Mock::given(method("POST"))
-                    .and(path("/codex/responses"))
-                    .respond_with(
-                        ResponseTemplate::new(200)
-                            .insert_header("content-type", "text/event-stream")
-                            .set_body_string(CAPTURE_COMPLETED_SSE),
-                    )
-                    .expect(1)
-                    .mount(&server)
-                    .await;
-                (
-                    server.uri(),
-                    Box::pin(async move {
-                        let requests = server.received_requests().await.unwrap();
-                        (
-                            requests[0].headers.clone(),
-                            captured_request_body(&requests[0]),
-                        )
-                    }),
-                )
-            };
-            let payload = payload(websocket);
-            let mut request_context = payload.context().clone();
-            let mut turn_metadata = metadata();
-            turn_metadata["installation_id"] = json!("client-installation");
-            request_context.insert("turn_metadata".into(), json!(turn_metadata.to_string()));
-            let mut stream = provider_with_base_url(&store, base_url)
-                .execute(
-                    planned_request(
-                        "openai",
-                        Operation::Generate(GenerateRequest::from_protocol_payload(
-                            payload.with_context(request_context),
-                        )),
-                    ),
-                    context_with_middleware(
-                        "req_parameters",
-                        Arc::new(ParametersMiddleware(Map::from_iter([(
-                            "installation_id".into(),
-                            json!(identity),
-                        )]))),
-                        FastMode::Default,
-                    ),
-                )
-                .await
-                .unwrap();
-            assert_eq!(
-                stream.metadata().provider_account_id().as_str(),
-                "acct_provider_contract"
-            );
-            while let Some(event) = stream.next().await {
-                event.unwrap();
-            }
-            let (headers, body) = capture.await;
-            assert_eq!(body["client_metadata"]["x-codex-installation-id"], identity);
-            let metadata: Value =
-                serde_json::from_str(headers["x-codex-turn-metadata"].to_str().unwrap()).unwrap();
-            assert_eq!(metadata["installation_id"], identity);
-            assert_eq!(
-                headers["session-id"].to_str().unwrap(),
-                body["client_metadata"]["session_id"]
-            );
-            captures.push((
-                body["client_metadata"]["session_id"].clone(),
-                body["prompt_cache_key"].clone(),
-            ));
-        }
-    }
-    assert_eq!(captures[0], captures[1]);
-    assert_eq!(captures[2], captures[3]);
-    assert_ne!(captures[0].0, captures[2].0);
-    assert_ne!(captures[0].1, captures[2].1);
-}
-
-#[tokio::test]
-async fn request_parameters_partition_new_websocket_chains_without_preventing_reuse() {
-    let store = Arc::new(MemoryAccountStore::default());
-    create_account(&store, "acct_provider_contract").await;
-    let listener = TcpListener::bind("127.0.0.1:0").await.unwrap();
-    let url = format!("http://{}", listener.local_addr().unwrap());
-    let identities = ["parameters-first", "parameters-second"];
-    let server = tokio::spawn(async move {
-        let mut retained = Vec::new();
-        for (index, identity) in identities.into_iter().enumerate() {
-            let (socket, _) = tokio::time::timeout(Duration::from_secs(3), listener.accept())
-                .await
-                .unwrap()
-                .unwrap();
-            let mut socket =
-                crate::transport::accept_codex_test_websocket_with(socket, |request, _| {
-                    let metadata: Value = serde_json::from_str(
-                        request.headers()["x-codex-turn-metadata"].to_str().unwrap(),
-                    )
-                    .unwrap();
-                    assert_eq!(metadata["installation_id"], identity);
-                })
-                .await;
-            for turn in 0..=index {
-                let text = tokio::time::timeout(Duration::from_secs(3), async {
-                    loop {
-                        match socket.next().await.unwrap().unwrap() {
-                            Message::Text(text) => break text,
-                            Message::Ping(payload) => {
-                                socket.send(Message::Pong(payload)).await.unwrap()
-                            }
-                            message => panic!("unexpected websocket frame: {message:?}"),
-                        }
-                    }
-                })
-                .await
-                .unwrap();
-                let body: Value = serde_json::from_str(&text).unwrap();
-                assert_eq!(body["client_metadata"]["x-codex-installation-id"], identity);
-                socket.send(Message::Text(json!({"type":"response.completed", "response":{
-                    "id":format!("resp_parameters_{index}_{turn}"), "model":"gpt-5.4", "status":"completed", "output":[]
-                }}).to_string().into())).await.unwrap();
-            }
-            // 保持旧连接可复用，证明新身份的隔离不是由测试服务端断开触发
-            retained.push(socket);
-        }
-    });
-    let provider = provider_with_base_url(&store, url);
-    for identity in [identities[0], identities[1], identities[1]] {
-        let payload = payload(true);
-        let mut request_context = payload.context().clone();
-        request_context.insert(
-            "turn_metadata".into(),
-            json!(json!({"installation_id":"client-installation"}).to_string()),
-        );
-        let mut stream = Arc::clone(&provider)
-            .execute(
-                planned_request(
-                    "openai",
-                    Operation::Generate(
-                        GenerateRequest::from_protocol_payload(
-                            payload.with_context(request_context),
-                        )
-                        .with_provider_session_state(
-                            ProviderSessionState::new(
-                                "openai",
-                                Map::from_iter([
-                                    ("account_id".into(), json!("acct_provider_contract")),
-                                    ("conversation_id".into(), json!("parameters-conversation")),
-                                    ("continuation_scope".into(), json!("persisted")),
-                                ]),
-                            )
-                            .unwrap(),
-                        ),
-                    ),
-                ),
-                context_with_middleware(
-                    "req_parameters_pool",
-                    Arc::new(ParametersMiddleware(Map::from_iter([(
-                        "installation_id".into(),
-                        json!(identity),
-                    )]))),
-                    FastMode::Default,
-                ),
-            )
-            .await
-            .unwrap();
-        tokio::time::timeout(Duration::from_secs(5), async {
-            while let Some(event) = stream.next().await {
-                event.unwrap();
-            }
-        })
-        .await
-        .unwrap();
-    }
-    server.await.unwrap();
-}
-
-#[tokio::test]
-async fn request_parameters_apply_to_images_and_search_without_reencoding_opaque_bodies() {
-    let store = Arc::new(MemoryAccountStore::default());
-    create_account(&store, "acct_provider_contract").await;
-    let server = MockServer::start().await;
-    Mock::given(method("POST"))
-        .respond_with(ResponseTemplate::new(200).set_body_json(json!({"data":[]})))
-        .expect(3)
-        .mount(&server)
-        .await;
-    let provider = provider_with_base_url(&store, server.uri());
-    let body = Bytes::from_static(br#"{ "future":1, "future":2 }"#);
-    let raw = RawJsonPayload::new("openai", body.clone())
-        .unwrap()
-        .with_context(Map::from_iter([(
-            "turn_metadata".into(),
-            json!(json!({"installation_id":"client-installation"}).to_string()),
-        )]));
-    for operation in [
-        Operation::GenerateImage(ImageRequest::from_raw_json(
-            ImageRequestKind::Generation,
-            raw.clone(),
-        )),
-        Operation::GenerateImage(ImageRequest::from_raw_json(
-            ImageRequestKind::Edit,
-            raw.clone(),
-        )),
-        Operation::Search(StandaloneSearchRequest::from_raw_json(raw)),
-    ] {
-        let mut stream = Arc::clone(&provider)
-            .execute(
-                planned_provider_endpoint_request("openai", operation),
-                context_with_middleware(
-                    "req_parameters_json",
-                    Arc::new(ParametersMiddleware(Map::from_iter([(
-                        "installation_id".into(),
-                        json!("plugin-installation"),
-                    )]))),
-                    FastMode::Default,
-                ),
-            )
-            .await
-            .unwrap();
-        while let Some(event) = stream.next().await {
-            event.unwrap();
-        }
-    }
-    for request in server.received_requests().await.unwrap() {
-        assert_eq!(request.body.as_slice(), body.as_ref());
-        let metadata: Value =
-            serde_json::from_str(request.headers["x-codex-turn-metadata"].to_str().unwrap())
-                .unwrap();
-        assert_eq!(metadata["installation_id"], "plugin-installation");
-    }
-}
-
-#[tokio::test]
-async fn invalid_request_parameters_fail_without_account_identity_fallback_or_send() {
-    let store = Arc::new(MemoryAccountStore::default());
-    create_account(&store, "acct_provider_contract").await;
-    let server = MockServer::start().await;
-    let provider = provider_with_base_url(&store, server.uri());
-    for parameters in [
-        json!({}),
-        json!({"installation_id":null}),
-        json!({"installation_id":42}),
-    ] {
-        let error = provider
-            .clone()
-            .execute(
-                planned_request("openai", http_generate_operation()),
-                context_with_middleware(
-                    "req_invalid_parameters",
-                    Arc::new(ParametersMiddleware(
-                        parameters.as_object().unwrap().clone(),
-                    )),
-                    FastMode::Default,
-                ),
-            )
-            .await
-            .err()
-            .expect("invalid parameters must fail");
-        assert_eq!(error.kind(), ProviderErrorKind::InvalidRequest);
-        assert_eq!(error.send_state(), UpstreamSendState::NotSent);
-        assert!(error.retry_is_prohibited());
-    }
-    assert!(server.received_requests().await.unwrap().is_empty());
-    Mock::given(method("POST"))
-        .and(path("/codex/responses"))
-        .respond_with(
-            ResponseTemplate::new(200)
-                .insert_header("content-type", "text/event-stream")
-                .set_body_string(CAPTURE_COMPLETED_SSE),
-        )
-        .expect(1)
-        .mount(&server)
-        .await;
-    let mut stream = provider
-        .execute(
-            planned_request("openai", http_generate_operation()),
-            context("req_after_invalid_parameters", CancellationToken::new()),
-        )
-        .await
-        .unwrap();
-    while let Some(event) = stream.next().await {
-        event.unwrap();
-    }
-}
-
 fn metadata() -> Value {
     json!({"session_id":"source-session", "thread_id":"source-thread", "turn_id":"source-turn",
         "parent_thread_id":"source-session", "forked_from_thread_id":"source-session",
diff --git a/backend/crates/providers/openai/tests/provider/live.rs b/backend/crates/providers/openai/tests/provider/live.rs
index debd6f08d..aad39f4a7 100644
--- a/backend/crates/providers/openai/tests/provider/live.rs
+++ b/backend/crates/providers/openai/tests/provider/live.rs
@@ -9,8 +9,8 @@ use gateway_core::account::{
     AccountModelAccess, AccountModelAccessMode, FastMode, ProviderAccountId, ProviderAccountStore,
 };
 use gateway_core::engine::middleware::{
-    MiddlewareContext, MiddlewareError, MiddlewareNext, MiddlewarePlan, MiddlewareRequest,
-    MiddlewareResponse,
+    MiddlewareContext, MiddlewareError, MiddlewareHeader, MiddlewareNext, MiddlewarePlan,
+    MiddlewareRequest, MiddlewareResponse,
 };
 use gateway_core::engine::provider::{Provider, ProviderRequest};
 use gateway_core::lifecycle::CancellationToken;
@@ -202,28 +202,8 @@ async fn live_bootstrap_preserves_model_through_middleware_and_metadata() {
     upstream.verify().await;
 }
 
-#[derive(Debug)]
-struct ParametersMiddleware;
-
-impl MiddlewarePlan for ParametersMiddleware {
-    fn handle(
-        &self,
-        _context: MiddlewareContext,
-        request: MiddlewareRequest,
-        next: MiddlewareNext,
-    ) -> BoxFuture<'static, Result<MiddlewareResponse, MiddlewareError>> {
-        assert!(request.provider_parameters().unwrap()["installation_id"].is_string());
-        next.run(
-            request.with_provider_parameters(serde_json::Map::from_iter([(
-                "installation_id".into(),
-                json!("live-plugin-installation"),
-            )])),
-        )
-    }
-}
-
 #[tokio::test]
-async fn live_create_uses_request_parameters_without_changing_call_ownership() {
+async fn live_create_uses_outbound_rewrite_without_changing_call_ownership() {
     let store = Arc::new(MemoryAccountStore::default());
     create_account(&store, ACCOUNT).await;
     let server = MockServer::start().await;
@@ -247,11 +227,16 @@ async fn live_create_uses_request_parameters_without_changing_call_ownership() {
     let mut stream = provider
         .execute(
             request,
-            context_with_middleware(
-                "req_live_parameters",
-                Arc::new(ParametersMiddleware),
-                FastMode::Default,
-            ),
+            super::contract::outbound_context("req_live_outbound", |request| {
+                request
+                    .headers
+                    .retain(|header| header.name() != "x-codex-turn-metadata");
+                request.headers.push(MiddlewareHeader::new(
+                    "x-codex-turn-metadata",
+                    Bytes::from(json!({"installation_id":"live-plugin-installation"}).to_string()),
+                ));
+                Ok(())
+            }),
         )
         .await
         .unwrap();
diff --git a/backend/crates/providers/xai/src/provider/mod.rs b/backend/crates/providers/xai/src/provider/mod.rs
index adebc33eb..bbe1e16ff 100644
--- a/backend/crates/providers/xai/src/provider/mod.rs
+++ b/backend/crates/providers/xai/src/provider/mod.rs
@@ -296,8 +296,7 @@ impl GrokBuildProvider {
                 provider_kind,
                 Some(model),
                 account_id,
-                None,
-                Box::new(move |operation, middleware_headers, _| {
+                Box::new(move |operation, middleware_headers| {
                     Box::pin(async move {
                         if let Some(adapter) = adapter {
                             return provider.execute_upstream_adapter(
diff --git a/docs/api.md b/docs/api.md
index 7c09f8d03..624b892b2 100644
--- a/docs/api.md
+++ b/docs/api.md
@@ -316,8 +316,8 @@ Responses 也不透传 `x-stainless-*`、`Origin`、`Referer`、`sec-ch-ua*` 和
 Images 的 `x-codex-image-turn-id` 和 Desktop 自动 Git 上下文的 `clientUserMessageId`。
 输入项元数据保持不变。Search 的会话 `id` 按同一安装身份域映射，只替换该值的原始字节，其余正文保持不变。
 `prompt_cache_key` 同样按安装身份映射，保留同一身份内的缓存共享关系；未提供时不补造。
-受信任插件可通过 attempt 构造参数选择本次安装身份；参数只影响出站构造，不改变实际选号与计费归属，
-详见 [SDK 请求构造参数](../backend/crates/gateway-plugin/sdk/docs/capabilities.md#模型请求与-attempt)。
+受信任插件可读取原始请求，自行生成身份并在 `outbound` 改写完整请求与关联字段；宿主不重新派生或补回业务字段，
+实际选号与计费归属保持不变，详见 [SDK 出站请求准备](../backend/crates/gateway-plugin/sdk/docs/capabilities.md#上游出站准备)。
 续接 response ID、历史 item/call ID、业务正文和未知扩展不参与映射，
 该处理减少显式追踪标识的跨账号复用，不保证会话内容或业务 metadata 无法关联
 
@@ -475,7 +475,7 @@ Images 排除已知为 Free 套餐的 OAuth 账号；套餐缺失或未知时不
 
 `/v1/alpha/search` 使用相同的 OpenAI Provider 原生端点边界：模型不映射，正文除会话 `id` 的账号归一及显式请求策略外原样转发，
 Provider 旁路读取请求中的 `model`，按[账号模型限制](#账号模型限制)选号。
-`x-codex-turn-metadata` 在移除客户端账号身份并按本次构造参数重写 installation ID 后转发；上游账号
+`x-codex-turn-metadata` 在移除客户端账号身份并按选中账号重写 installation ID 后转发；上游账号
 Authorization、Cookie、account ID、originator 和 User-Agent 均由代理安全重建。
 Images 与 Search 保留通过现有过滤规则的普通业务请求头及多值字节；Responses 原连接的 turn state
 不随独立端点转发，turn metadata 仍由所属端点按当前账号处理。
diff --git a/docs/architecture.md b/docs/architecture.md
index cbfb0cea1..ae0837aa1 100644
--- a/docs/architecture.md
+++ b/docs/architecture.md
@@ -172,8 +172,6 @@ flowchart LR
   握手、socket 与断连由 API 持有，会话处理通过原 RPC 资源流保活；HTTP 返回链替换响应时释放未提交的会话。
   原生与插件接管的下游 WebSocket 共用消息组合和取消入口，在默认解析前和实际写入前处理完整消息；读写并发进行，插件调用期间不占用 transport 写锁。
   `request` 包裹逻辑模型请求，`attempt` 包裹每次已选号的执行；请求顺序进入、响应逆序返回。
-  attempt 可携带 Provider 的本次构造参数，Core / Runtime 只传递完整替换后的对象，解释和缺失校验由 Provider 负责；
-  参数不改变真实租约、凭据版本和计费归属，也不承载宿主对插件策略的推断、补值或持久化。
   `outbound` 在原生默认值、隐私处理、序列化及内容压缩之后组合完整请求，续体只准备值，Provider 在整条返回链结束后发送。
   无绑定或未命中当前请求范围时保留原生请求构造，不进入出站准备链。
   它复用本次 attempt 的冻结计划、取消、期限和副作用水位；Provider 不再次应用业务默认值或重写正文，插件负责报文与内容编码的一致性。
@@ -467,7 +465,7 @@ OpenAI 模型目录用于发现，不因目录缺项拒绝请求；管理员配
 - OpenAI 是透明边界。正文兼容、身份归一和显式请求策略之外的业务字段保留原始语义；
   业务响应按原始字节转发，客户端错误兼容与原生续写额度恢复按明确例外处理，见 [OpenAI 透传](api.md#openai-透传)。
   `transport/correlation` 在出站副本上按本次安装身份统一映射关联标识并剥离客户端 trace；
-  安装身份默认取自账号，可由 attempt 的构造参数改写，缺失或非法结果不回退默认值。
+  原生安装身份取自账号；插件的身份生成、持久化及关联字段改写通过既有中间件链路自行完成。
   内部选号、亲和、连接池与本地诊断继续读取原始身份；具体字段边界见 [API 协议](api.md#请求头与身份)
   canonical facts 从同一数据旁路提取，用于路由、恢复判断、观测和计费。
   WebSocket transport 按完整文本消息交付，wire 同时保留原文与可选解析视图；同协议出口使用原文，