diff --git a/contracts/agents-api/sessions-events.md b/contracts/agents-api/sessions-events.md
index 1f5fda736..2d4d4323f 100644
--- a/contracts/agents-api/sessions-events.md
+++ b/contracts/agents-api/sessions-events.md
@@ -48,7 +48,7 @@ A Session stays usable after a Turn fails: new input starts a new Turn. Later re
 - **Limits.** The request body is at most 1 MiB, and the stored input of one request at most 512 KiB.
 - **Null batch.** An explicit `null` for `events` is invalid.
 - **Empty batch.** `{"events": []}` checks that the Session exists and returns 202. It creates no Turn, Item or retry identity.
-- **Retries.** An `Idempotency-Key` of up to 128 bytes identifies the whole ordered batch. The same key and batch return 202 again without admitting anything twice; the same key with another batch returns 409 `idempotency_conflict`. A request without a key is always new.
+- **Retries.** An `Idempotency-Key` of 1–256 bytes identifies the whole ordered batch; an empty or longer key returns 400. The same key and batch return 202 again without admitting anything twice; the same key with another batch returns 409 `idempotency_conflict`. A request without a key is always new.
 - **Messages.** On an idle Session a message batch starts a queued Turn. While a Turn runs, messages join it (steering); they never start a parallel Turn. Each message stays its own user Item, even when the Harness receives several as one prompt.
 - **Cancellation.** A queued Turn is cancelled without a live Runtime. A running Turn is cancelled when the Runtime confirms it; completion can win that race. The Turn has stopped when it reads `cancelled`, not when the request returns. A Turn that waits for a function result keeps the Session at `requires_action` with its `required_actions` until then, and the request emits no Session event. A cancellation on an idle Session with no pending input is accepted and has no effect; while an input reservation is pending, it returns 409.
 - **Function results.** `turn_id`, `call_id` and `success` are required; `output` and `error` are optional and nullable ([content rules](./message-content.md#function-results)). An identical repeated result returns 202 without another application or event. The result Item appears when the Harness applies the result; a result that cancellation prevents from being applied stays stored but produces no Item.
diff --git a/contracts/agents-api/wire-semantics.md b/contracts/agents-api/wire-semantics.md
index cf7147995..e18303bd9 100644
--- a/contracts/agents-api/wire-semantics.md
+++ b/contracts/agents-api/wire-semantics.md
@@ -239,7 +239,7 @@ Creation validates the body and metadata types, the request fields and initial i
 
 ### Creation retries
 
-Send an `Idempotency-Key` of 1–128 bytes that is not only whitespace; a longer or whitespace-only key returns 400 `invalid_request`. An empty header counts as no key. Without a key, every request creates a new Session. The official service creates a new Session for each request even with the same key; Core returns the original one.
+Send an `Idempotency-Key` of 1–256 bytes; a longer key returns 400 `invalid_request`. An empty header counts as no key. Without a key, every request creates a new Session. The official service creates a new Session for each request even with the same key; Core returns the original one.
 
 | Case | Response |
 | --- | --- |
diff --git a/contracts/agents-api/zh/sessions-events.md b/contracts/agents-api/zh/sessions-events.md
index ff512094e..00d3637cc 100644
--- a/contracts/agents-api/zh/sessions-events.md
+++ b/contracts/agents-api/zh/sessions-events.md
@@ -1,7 +1,7 @@
 ---
 title: "Session、事件和历史"
 source: contracts/agents-api/sessions-events.md
-source_hash: 180e08dbdd9c85ae85005cc202f73316f2b1b04828cca67df13b804206f49f02
+source_hash: 1c6e57bbd212f7155906d68bbbcb2e976170512a2aca907e024104667419d720
 ---
 
 本契约涵盖 Session 内部发生的事情：发送输入、实时事件流，以及读取 Turn、Item 和使用量的持久化历史。Session 资源本身（创建配置、重试标识、更新、列出和删除）见 [API 行为](wire-semantics.md)。消息和函数结果内容见[消息内容](message-content.md)。[Agents API 指南](../../../docs/zh/api/public-agent-api.md)展示了使用 SDK 和 HTTP 的调用方式。
@@ -50,7 +50,7 @@ Turn 失败后 Session 仍可使用：新输入会启动一个新 Turn。后来
 - **限制。** 请求正文最多为 1 MiB，单次请求存储的输入最多为 512 KiB。
 - **空值批次。** 将 `events` 显式设为 `null` 无效。
 - **空批次。** `{"events": []}` 会检查 Session 是否存在并返回 202。它不会创建 Turn、Item 或重试标识。
-- **重试。** 最长 128 字节的 `Idempotency-Key` 标识整个有序批次。相同密钥和批次会再次返回 202，而不会重复接纳任何内容；相同密钥搭配另一个批次会返回 409 `idempotency_conflict`。不带密钥的请求始终是新请求。
+- **重试。** 1–256 字节的 `Idempotency-Key` 标识整个有序批次；空键或更长的键返回 400。相同密钥和批次会再次返回 202，而不会重复接纳任何内容；相同密钥搭配另一个批次会返回 409 `idempotency_conflict`。不带密钥的请求始终是新请求。
 - **消息。** 在空闲 Session 上，消息批次会启动一个排队的 Turn。Turn 运行时，消息会加入其中（引导）；它们绝不会启动并行 Turn。每条消息都保留为独立的用户 Item，即使 Harness 将多条消息作为同一个提示接收。
 - **取消。** 排队的 Turn 无需活动 Runtime 即可取消。正在运行的 Turn 只有在 Runtime 确认后才会取消；完成操作可能赢得该竞争。读取到 `cancelled` 时才表示该 Turn 已停止，而不是请求返回时。正在等待函数结果的 Turn 在此之前会让 Session 保持 `requires_action` 及其 `required_actions`，且该请求不会发出 Session 事件。在没有待处理输入的情况下，对空闲 Session 执行的取消会被接受且不产生任何效果；而在输入预留待处理期间，取消会返回 409。
 - **函数结果。** `turn_id`、`call_id` 和 `success` 为必填项；`output` 和 `error` 为可选项且可为空（[内容规则](message-content.md#function-results)）。重复提交完全相同的结果会返回 202，不会再次应用或发出事件。Harness 应用结果时才会出现结果 Item；如果取消操作导致结果无法应用，结果仍会存储，但不会产生 Item。
diff --git a/contracts/agents-api/zh/wire-semantics.md b/contracts/agents-api/zh/wire-semantics.md
index 0de791bb5..ad653897c 100644
--- a/contracts/agents-api/zh/wire-semantics.md
+++ b/contracts/agents-api/zh/wire-semantics.md
@@ -1,7 +1,7 @@
 ---
 title: "API 行为"
 source: contracts/agents-api/wire-semantics.md
-source_hash: 29a928dc41487b9e5a11cdeff7305d2f006040822caf66b299e504cb8eab9662
+source_hash: abb76393a7bc5669970b2fd7156f6293143b12949f0517fc8061737f51c73d32
 ---
 
 已锁定版本的 OpenAI Python SDK（[upstream.json](https://github.com/MiniMax-AI/OpenAgentCore/blob/main/contracts/agents-api/upstream.json)）定义了 `/v1` 路由、字段和类型。本页面说明这些类型未作规定之处 Core 的行为，例如状态码、错误字段、默认值和列表边界，以及 Core 与官方服务存在差异的地方。[OpenAI 兼容性](index.md) 列出了这些差异和尚存缺口；[Sessions, events and history](sessions-events.md)、[message content](message-content.md)、[Vaults](vaults.md)、[source Files and Skills](source-files.md) 和 [Environment files and Artifacts](environment-files.md) 分别负责各自资源的规则。
@@ -241,7 +241,7 @@ Session 创建会将 Agent 的有效配置复制到不可变快照中。使用 `
 
 ### 创建重试 {#creation-retries}
 
-发送一个 1–128 字节且不只包含空白字符的 `Idempotency-Key`；更长或仅包含空白字符的键会返回 400 `invalid_request`。空标头视为未提供键。没有键时，每个请求都会创建一个新的 Session。官方服务即使收到相同的键，也会为每个请求创建新的 Session；Core 则返回原有 Session。
+发送一个 1–256 字节的 `Idempotency-Key`；更长的键会返回 400 `invalid_request`。空标头视为未提供键。没有键时，每个请求都会创建一个新的 Session。官方服务即使收到相同的键，也会为每个请求创建新的 Session；Core 则返回原有 Session。
 
 | 情况 | 响应 |
 | --- | --- |
diff --git a/docs/api/public-agent-api.md b/docs/api/public-agent-api.md
index fa7764420..6fe6be650 100644
--- a/docs/api/public-agent-api.md
+++ b/docs/api/public-agent-api.md
@@ -109,7 +109,7 @@ Two lists differ: `GET /files` returns up to 10,000 files at once, and workspace
 
 ### Idempotency
 
-Send an `Idempotency-Key` (up to 128 bytes) when creating a Session or sending input. A retry with the same key and body returns the original result instead of doing the work twice. The same key with a different body fails with 409 `idempotency_conflict`.
+Send an `Idempotency-Key` (1–256 bytes) when creating a Session or sending input. A retry with the same key and body returns the original result instead of doing the work twice. The same key with a different body fails with 409 `idempotency_conflict`.
 
 ```python
 import uuid
diff --git a/docs/zh/api/public-agent-api.md b/docs/zh/api/public-agent-api.md
index 73e3f4ecd..4d850bb19 100644
--- a/docs/zh/api/public-agent-api.md
+++ b/docs/zh/api/public-agent-api.md
@@ -1,7 +1,7 @@
 ---
 title: "Agents API 指南"
 source: docs/api/public-agent-api.md
-source_hash: 1db2045ded2e2bf523dd94a3db08c5ac6078bf76489f7cb09de092164e89aa8c
+source_hash: bd942f9e71b26493c6d1c3b0dc6fd57e6781a34a6d8597d8559acfdc6c7b8a2a
 ---
 
 Core 在 `/v1` 提供 OpenAI Agents API。本指南用官方 OpenAI SDK 和普通 HTTP 两种方式演示每项常见任务，并说明 Core 与 OpenAI 的差异。如果尚未启动过 Session，请先阅读[运行第一个 Session](../getting-started/quickstart.md)。
@@ -111,7 +111,7 @@ agents "/agents/sessions?limit=100&after=$LAST_ID"
 
 ### 幂等性 {#idempotency}
 
-创建 Session 或发送输入时，请发送 `Idempotency-Key`（最长 128 字节）。使用相同密钥和正文重试时，会返回原始结果，而不会重复执行工作。相同密钥搭配不同正文会失败，并返回 409 `idempotency_conflict`。
+创建 Session 或发送输入时，请发送 `Idempotency-Key`（1–256 字节）。使用相同密钥和正文重试时，会返回原始结果，而不会重复执行工作。相同密钥搭配不同正文会失败，并返回 409 `idempotency_conflict`。
 
 ```python
 import uuid
diff --git a/services/core/internal/api/inputs.go b/services/core/internal/api/inputs.go
index b17bd5d38..ef552cb7e 100644
--- a/services/core/internal/api/inputs.go
+++ b/services/core/internal/api/inputs.go
@@ -29,10 +29,10 @@ func (h *Handler) createEvents(w http.ResponseWriter, r *http.Request) {
 	}
 	_ = json.Unmarshal(raw, &request)
 	key := r.Header.Get("Idempotency-Key")
-	if key == "" {
+	if len(r.Header.Values("Idempotency-Key")) == 0 {
 		key = uuid.NewString()
 	}
-	if err := sessions.ValidateInputKey(key); err != nil {
+	if err := sessions.ValidateIdempotencyKey(key); err != nil {
 		writeSessionsError(w, r, err)
 		return
 	}
diff --git a/services/core/internal/api/session_semantics_test.go b/services/core/internal/api/session_semantics_test.go
index 2cb5b1ceb..2e0562386 100644
--- a/services/core/internal/api/session_semantics_test.go
+++ b/services/core/internal/api/session_semantics_test.go
@@ -60,7 +60,7 @@ func TestEmptyEventBatchAuthorizesWithoutExecutionEffects(t *testing.T) {
 				}
 			}
 			reads := sessions.reads
-			for _, key := range []string{" ", strings.Repeat("x", 129)} {
+			for _, key := range []string{"", strings.Repeat("x", 257)} {
 				if w := request("owned", "test-api-key", key); w.Code != http.StatusBadRequest || sessions.reads != reads {
 					t.Fatalf("invalid identity reached resource: %d %s", w.Code, w.Body)
 				}
diff --git a/services/core/internal/sessions/creation.go b/services/core/internal/sessions/creation.go
index bea48eddd..1bd27eaa1 100644
--- a/services/core/internal/sessions/creation.go
+++ b/services/core/internal/sessions/creation.go
@@ -332,7 +332,7 @@ func prepareCreation(input CreateSession, fingerprint func(string) (string, erro
 		return NewSession{}, nil, nil, fmt.Errorf("%w: %v", ErrInvalidInput, err)
 	}
 	engine := strings.TrimSpace(input.Engine)
-	if !ValidEngine(engine) || !validCreationKey(input.IdempotencyKey) {
+	if !ValidEngine(engine) || ValidateIdempotencyKey(input.IdempotencyKey) != nil {
 		return NewSession{}, nil, nil, fmt.Errorf("%w: engine and idempotency key are required", ErrInvalidInput)
 	}
 	labels := input.Metadata
@@ -417,10 +417,6 @@ func prepareCreation(input CreateSession, fingerprint func(string) (string, erro
 	}, batch, encodedInput, nil
 }
 
-func validCreationKey(key string) bool {
-	return strings.TrimSpace(key) != "" && len(key) <= 128
-}
-
 // fingerprintedProvider replaces a bundle's key with its keyed fingerprint.
 func fingerprintedProvider(provider *v1.ModelProviderInput, fingerprint func(string) (string, error)) (*v1.ModelProviderInput, error) {
 	if provider == nil {
@@ -505,8 +501,8 @@ func (s *Service) FindSessionCreation(ctx context.Context, tenant, key string, r
 	if err := creator.Validate(); err != nil {
 		return Creation{}, fmt.Errorf("%w: %v", ErrInvalidInput, err)
 	}
-	if !validCreationKey(key) {
-		return Creation{}, ErrInvalidInput
+	if err := ValidateIdempotencyKey(key); err != nil {
+		return Creation{}, err
 	}
 	hash, err := intentHash(request, s.storage.FingerprintProviderKey)
 	if err != nil {
diff --git a/services/core/internal/sessions/creation_test.go b/services/core/internal/sessions/creation_test.go
index 48b2bb70a..10e21d25d 100644
--- a/services/core/internal/sessions/creation_test.go
+++ b/services/core/internal/sessions/creation_test.go
@@ -218,8 +218,8 @@ func TestPrepareCreation(t *testing.T) {
 	}{
 		"invalid creator": {func(input *CreateSession) { input.Creator = identity.Subject{} }, fingerprints, ErrInvalidInput},
 		"invalid engine":  {func(input *CreateSession) { input.Engine = "Codex" }, fingerprints, ErrInvalidInput},
-		"blank key":       {func(input *CreateSession) { input.IdempotencyKey = " " }, fingerprints, ErrInvalidInput},
-		"long key":        {func(input *CreateSession) { input.IdempotencyKey = strings.Repeat("k", 129) }, fingerprints, ErrInvalidInput},
+		"empty key":       {func(input *CreateSession) { input.IdempotencyKey = "" }, fingerprints, ErrInvalidInput},
+		"long key":        {func(input *CreateSession) { input.IdempotencyKey = strings.Repeat("k", 257) }, fingerprints, ErrInvalidInput},
 		"configuration over 512K": {func(input *CreateSession) {
 			input.Configuration = json.RawMessage(`"` + strings.Repeat("x", 512*1024) + `"`)
 		}, fingerprints, ErrInvalidInput},
@@ -604,7 +604,7 @@ func TestFindSessionCreation(t *testing.T) {
 		{"missing creation", "create", request, creator, fingerprints, func() (CreationRecord, error) { return CreationRecord{}, ErrNotFound }, ErrNotFound, []string{"FindCreation tenant create"}},
 		{"another creator", "create", request, identity.Subject{Kind: "user", ID: "stranger"}, fingerprints, found, ErrIdempotencyConflict, []string{"FindCreation tenant create"}},
 		{"no intent", "create", nil, creator, nil, nil, ErrInvalidInput, nil},
-		{"invalid key", " ", request, creator, nil, nil, ErrInvalidInput, nil},
+		{"invalid key", "", request, creator, nil, nil, ErrInvalidInput, nil},
 		{"invalid creator", "create", request, identity.Subject{}, nil, nil, ErrInvalidInput, nil},
 	} {
 		t.Run(test.name, func(t *testing.T) {
diff --git a/services/core/internal/sessions/environment_creation.go b/services/core/internal/sessions/environment_creation.go
index 0023c0c66..7e056a701 100644
--- a/services/core/internal/sessions/environment_creation.go
+++ b/services/core/internal/sessions/environment_creation.go
@@ -153,8 +153,8 @@ func (s *Service) environmentIdentity(key string, creator identity.Subject, requ
 	if err := creator.Validate(); err != nil {
 		return EnvironmentIdentity{}, fmt.Errorf("%w: %v", ErrInvalidInput, err)
 	}
-	if key == "" || len(key) > 256 {
-		return EnvironmentIdentity{}, ErrInvalidInput
+	if err := ValidateIdempotencyKey(key); err != nil {
+		return EnvironmentIdentity{}, err
 	}
 	hash, err := intentHash(request, s.storage.FingerprintProviderKey)
 	if err != nil {
diff --git a/services/core/internal/sessions/environment_inputs.go b/services/core/internal/sessions/environment_inputs.go
index 12842af11..2619963cd 100644
--- a/services/core/internal/sessions/environment_inputs.go
+++ b/services/core/internal/sessions/environment_inputs.go
@@ -37,7 +37,7 @@ func joinsActiveTurn(turn Turn, active bool) bool {
 // passed, or the receipts the batch was admitted with. The checks of
 // SubmitInputs apply, and a failed or expired Environment rejects new input.
 func (s *Service) ReserveEnvironmentInput(ctx context.Context, tenant, session, key string, inputs []Input) (EnvironmentInputReservation, error) {
-	if err := ValidateInputKey(key); err != nil {
+	if err := ValidateIdempotencyKey(key); err != nil {
 		return EnvironmentInputReservation{}, err
 	}
 	batch, encoded, err := validateMessageInputs(inputs)
diff --git a/services/core/internal/sessions/inputs.go b/services/core/internal/sessions/inputs.go
index 458d78230..47dcf7dd8 100644
--- a/services/core/internal/sessions/inputs.go
+++ b/services/core/internal/sessions/inputs.go
@@ -5,7 +5,6 @@ import (
 	"encoding/json"
 	"fmt"
 	"slices"
-	"strings"
 	"time"
 
 	"github.com/MiniMax-AI/OpenAgentCore/services/core/internal/jsonobject"
@@ -31,10 +30,11 @@ type TurnInput struct {
 	CreatedAt time.Time
 }
 
-// ValidateInputKey enforces the shared request identity limit, including no-op requests.
-func ValidateInputKey(key string) error {
-	if strings.TrimSpace(key) == "" || len(key) > 128 {
-		return fmt.Errorf("%w: idempotency key is required and limited to 128 bytes", ErrInvalidInput)
+// ValidateIdempotencyKey enforces the pinned Idempotency-Key bound of 1 to 256
+// bytes on every request identity, including no-op requests.
+func ValidateIdempotencyKey(key string) error {
+	if key == "" || len(key) > 256 {
+		return fmt.Errorf("%w: idempotency key must be 1 to 256 bytes", ErrInvalidInput)
 	}
 	return nil
 }
@@ -331,7 +331,7 @@ type InputReader interface {
 // (ErrInputPending). Internal receipts are not the response body of the
 // public events endpoint.
 func (s *Service) SubmitInputs(ctx context.Context, tenant, session, key string, inputs []Input) ([]InputReceipt, error) {
-	if err := ValidateInputKey(key); err != nil {
+	if err := ValidateIdempotencyKey(key); err != nil {
 		return nil, err
 	}
 	batch, encoded, err := ValidateInputs(inputs)
diff --git a/services/core/internal/sessions/inputs_test.go b/services/core/internal/sessions/inputs_test.go
index 7006692bc..ffbf958cc 100644
--- a/services/core/internal/sessions/inputs_test.go
+++ b/services/core/internal/sessions/inputs_test.go
@@ -326,7 +326,7 @@ func TestSubmitInputs(t *testing.T) {
 	})
 	t.Run("an invalid request touches no storage", func(t *testing.T) {
 		service := deviceService(t, &fakeStorage{t: t})
-		if _, err := service.SubmitInputs(t.Context(), testTenant, testSession, " ", inputs); !errors.Is(err, ErrInvalidInput) {
+		if _, err := service.SubmitInputs(t.Context(), testTenant, testSession, "", inputs); !errors.Is(err, ErrInvalidInput) {
 			t.Fatal(err)
 		}
 		if _, err := service.SubmitInputs(t.Context(), testTenant, testSession, inputKey, nil); !errors.Is(err, ErrInvalidInput) {
@@ -334,3 +334,11 @@ func TestSubmitInputs(t *testing.T) {
 		}
 	})
 }
+
+func TestIdempotencyKeyIsOneTo256Bytes(t *testing.T) {
+	for key, valid := range map[string]bool{"": false, "k": true, strings.Repeat("k", 256): true, strings.Repeat("k", 257): false} {
+		if (ValidateIdempotencyKey(key) == nil) != valid {
+			t.Error("key length", len(key))
+		}
+	}
+}