fix(openai-ws): share immutable replay bodies to stop O(T²) copying

OpenAI Responses WS/HTTP-bridge 的 replay 历史此前每轮对全部正文做多次
深拷贝（构建、双份序列、保存点各一遍），长会话累计分配 O(T²)，实测
128 turn x 10KiB 达 160MB+，是 #6382 内存持续增长直至 OOM 的主因。

改为共享不可变正文所有权：
- extract 经零拷贝 string 视图 + gjson Index 直接切 payload 子切片，
  并以 json.Valid 保持对断裂数组的既有错误语义
- 序列构建/sanitize/collector/保存点全部只传引用；跨持有者保存经
  combineOpenAIWSReplayItems 新建头数组，正文不复制
- bridge 每轮一次解析，正常 replay 与 account-failover 序列共享正文
- 前缀比较增加字节级快路径，避免逐轮全历史 decode+encode
- strict 状态可用时不再整包保留上一轮 payload

新增 128 turn 分配回归测试锚定上界（实测 2.5MB，深拷贝回归会击穿），
以及正文共享的所有权断言。

backend/internal/service/openai_ws_forwarder_ingress.go

@@ -586,24 +586,27 @@ func (s *OpenAIGatewayService) ProxyResponsesWebSocketFromClient(
 			toolOutputCoverage := AnalyzeToolCallOutputContextCoverageBytes(currentBridgePayload.payloadRaw)
 			needsBridgeReplay := currentBridgePayload.previousResponseID != "" ||
 				(toolOutputCoverage.HasFunctionCallOutput && !toolOutputCoverage.ContextCoversAllCallIDs)
-			turnReplayInput, turnReplayInputExists, replayInputErr := buildOpenAIWSReplayInputSequence(
+			// 一次解析当前 input，正常 replay 与 account-failover 两份序列共享同一批正文。
+			bridgeCurrentItems, bridgeCurrentItemsExist, extractErr := openAIWSExtractNormalizedInputSequence(
+				currentBridgePayload.payloadRaw,
+			)
+			if extractErr != nil {
+				return fmt.Errorf("build websocket http bridge replay input: %w", extractErr)
+			}
+			turnReplayInput, turnReplayInputExists := buildOpenAIWSReplayInputSequenceFromItems(
 				bridgeReplayInput,
 				bridgeReplayInputExists,
-				currentBridgePayload.payloadRaw,
+				bridgeCurrentItems,
+				bridgeCurrentItemsExist,
 				needsBridgeReplay,
 			)
-			if replayInputErr != nil {
-				return fmt.Errorf("build websocket http bridge replay input: %w", replayInputErr)
-			}
-			turnAccountFailoverInput, turnAccountFailoverInputExists, failoverInputErr := buildOpenAIWSReplayInputSequence(
+			turnAccountFailoverInput, turnAccountFailoverInputExists := buildOpenAIWSReplayInputSequenceFromItems(
 				bridgeAccountFailoverInput,
 				bridgeAccountFailoverInputExists,
-				currentBridgePayload.payloadRaw,
+				bridgeCurrentItems,
+				bridgeCurrentItemsExist,
 				needsBridgeReplay,
 			)
-			if failoverInputErr != nil {
-				return fmt.Errorf("build websocket account failover input: %w", failoverInputErr)
-			}
 			if needsBridgeReplay && turnReplayInputExists {
 				updatedPayload, setInputErr := setOpenAIWSPayloadInputSequence(
 					currentBridgePayload.payloadRaw,
@@ -680,18 +683,20 @@ func (s *OpenAIGatewayService) ProxyResponsesWebSocketFromClient(
 			if result == nil {
 				return errors.New("websocket http bridge turn result is nil")
 			}
-			bridgeReplayInput = cloneOpenAIWSRawMessages(turnReplayInput)
+			// turnReplayInput/turnAccountFailoverInput 可能共享同一头数组（转移自
+			// bridgeCurrentItems），保存历史必须经 combine 新建头，禁止就地 append。
+			bridgeReplayInput = turnReplayInput
 			bridgeReplayInputExists = turnReplayInputExists
 			if result.wsReplayInputExists {
-				bridgeReplayInput = append(bridgeReplayInput, cloneOpenAIWSRawMessages(result.wsReplayInput)...)
+				bridgeReplayInput = combineOpenAIWSReplayItems(bridgeReplayInput, result.wsReplayInput)
 				bridgeReplayInputExists = true
 			}
-			bridgeAccountFailoverInput = cloneOpenAIWSRawMessages(turnAccountFailoverInput)
+			bridgeAccountFailoverInput = turnAccountFailoverInput
 			bridgeAccountFailoverInputExists = turnAccountFailoverInputExists
 			if len(result.wsAccountFailoverReplayInput) > 0 {
-				bridgeAccountFailoverInput = append(
+				bridgeAccountFailoverInput = combineOpenAIWSReplayItems(
 					bridgeAccountFailoverInput,
-					cloneOpenAIWSRawMessages(result.wsAccountFailoverReplayInput)...,
+					result.wsAccountFailoverReplayInput,
 				)
 				bridgeAccountFailoverInputExists = true
 			}
@@ -1744,16 +1749,19 @@ func (s *OpenAIGatewayService) ProxyResponsesWebSocketFromClient(
 		}
 		responseID := strings.TrimSpace(result.RequestID)
 		lastTurnResponseID = responseID
-		lastTurnPayload = cloneOpenAIWSPayloadBytes(currentPayload)
-		lastTurnReplayInput = cloneOpenAIWSRawMessages(currentTurnReplayInput)
+		// 正文共享：currentPayload/currentTurnReplayInput 均不可变，历史直接引用；
+		// collector 增量经 combine 合并（新头数组）。
+		lastTurnReplayInput = currentTurnReplayInput
 		lastTurnReplayInputExists = currentTurnReplayInputExists
 		if result.wsReplayInputExists {
-			lastTurnReplayInput = append(lastTurnReplayInput, cloneOpenAIWSRawMessages(result.wsReplayInput)...)
+			lastTurnReplayInput = combineOpenAIWSReplayItems(lastTurnReplayInput, result.wsReplayInput)
 			lastTurnReplayInputExists = true
 		}
 		nextStrictState, strictStateErr := buildOpenAIWSIngressPreviousTurnStrictState(currentPayload)
 		if strictStateErr != nil {
 			lastTurnStrictState = nil
+			// strict 状态不可用时保留整份上一轮 payload 供慢路径比较。
+			lastTurnPayload = currentPayload
 			logOpenAIWSModeInfo(
 				"ingress_ws_prev_response_strict_state_skip account_id=%d turn=%d conn_id=%s reason=build_error cause=%s",
 				account.ID,
@@ -1763,6 +1771,7 @@ func (s *OpenAIGatewayService) ProxyResponsesWebSocketFromClient(
 			)
 		} else {
 			lastTurnStrictState = nextStrictState
+			lastTurnPayload = nil
 		}
 
 		if responseID != "" && stateStore != nil {

backend/internal/service/openai_ws_forwarder_ingress_test.go

@@ -1,6 +1,7 @@
 package service
 
 import (
+	"bytes"
 	"context"
 	"encoding/json"
 	"errors"
@@ -1007,18 +1008,79 @@ func TestSetOpenAIWSPayloadInputSequence(t *testing.T) {
 	})
 }
 
-func TestCloneOpenAIWSRawMessages(t *testing.T) {
+func TestCombineOpenAIWSReplayItems(t *testing.T) {
 	t.Parallel()
 
-	t.Run("nil_slice", func(t *testing.T) {
-		cloned := cloneOpenAIWSRawMessages(nil)
-		require.Nil(t, cloned)
+	t.Run("empty_delta_returns_history", func(t *testing.T) {
+		history := []json.RawMessage{json.RawMessage(`{"a":1}`)}
+		require.Nil(t, combineOpenAIWSReplayItems(nil, nil))
+		combined := combineOpenAIWSReplayItems(history, nil)
+		require.Len(t, combined, 1)
 	})
 
-	t.Run("empty_slice", func(t *testing.T) {
-		items := make([]json.RawMessage, 0)
-		cloned := cloneOpenAIWSRawMessages(items)
-		require.NotNil(t, cloned)
-		require.Len(t, cloned, 0)
+	t.Run("new_header_shares_bodies", func(t *testing.T) {
+		history := []json.RawMessage{json.RawMessage(`{"a":1}`)}
+		delta := []json.RawMessage{json.RawMessage(`{"b":2}`)}
+		combined := combineOpenAIWSReplayItems(history, delta)
+		require.Len(t, combined, 2)
+		// 头数组必须是新建的：对 combined 追加不影响 history。
+		require.NotSame(t, &history[0], &combined[0])
+		// 正文共享：不发生字节级深拷贝。
+		require.Same(t, &history[0][0], &combined[0][0])
+		require.Same(t, &delta[0][0], &combined[1][0])
+	})
+}
+
+func TestOpenAIWSReplaySequenceSharesBodies(t *testing.T) {
+	t.Parallel()
+
+	t.Run("extract_shares_payload_backing_array", func(t *testing.T) {
+		payload := []byte(`{"input":[{"type":"input_text","text":"hello"},{"type":"input_text","text":"world"}]}`)
+		items, exists, err := openAIWSExtractNormalizedInputSequence(payload)
+		require.NoError(t, err)
+		require.True(t, exists)
+		require.Len(t, items, 2)
+		for _, item := range items {
+			start := bytes.Index(payload, []byte(item))
+			require.GreaterOrEqual(t, start, 0)
+			require.Same(t, &payload[start], &item[0], "extract 应零拷贝共享 payload 底层数组")
+		}
+	})
+
+	t.Run("build_transfers_current_items_ownership", func(t *testing.T) {
+		payload := []byte(`{"input":[{"type":"input_text","text":"hello"}]}`)
+		items, exists, err := buildOpenAIWSReplayInputSequence(nil, false, payload, false)
+		require.NoError(t, err)
+		require.True(t, exists)
+		require.Len(t, items, 1)
+		start := bytes.Index(payload, []byte(items[0]))
+		require.GreaterOrEqual(t, start, 0)
+		require.Same(t, &payload[start], &items[0][0])
+	})
+
+	t.Run("build_merge_shares_history_bodies", func(t *testing.T) {
+		history := []json.RawMessage{json.RawMessage(`{"type":"input_text","text":"hello"}`)}
+		items, exists, err := buildOpenAIWSReplayInputSequence(
+			history,
+			true,
+			[]byte(`{"previous_response_id":"resp_1","input":[{"type":"input_text","text":"world"}]}`),
+			true,
+		)
+		require.NoError(t, err)
+		require.True(t, exists)
+		require.Len(t, items, 2)
+		require.Same(t, &history[0][0], &items[0][0], "历史正文应共享而非深拷贝")
+	})
+
+	t.Run("build_prefix_hit_transfers_current_items", func(t *testing.T) {
+		history := []json.RawMessage{json.RawMessage(`{"type":"input_text","text":"hello"}`)}
+		payload := []byte(`{"previous_response_id":"resp_1","input":[{"type":"input_text","text":"hello"},{"type":"input_text","text":"world"}]}`)
+		items, exists, err := buildOpenAIWSReplayInputSequence(history, true, payload, true)
+		require.NoError(t, err)
+		require.True(t, exists)
+		require.Len(t, items, 2)
+		start := bytes.Index(payload, []byte(items[1]))
+		require.GreaterOrEqual(t, start, 0)
+		require.Same(t, &payload[start], &items[1][0], "prefix 命中应转移当前 items 所有权并共享 payload 底层数组")
 	})
 }

backend/internal/service/openai_ws_forwarder_payload.go

@@ -9,6 +9,7 @@ import (
 	"net/http"
 	"net/url"
 	"strings"
+	"unsafe"
 
 	"github.com/gin-gonic/gin"
 	"github.com/tidwall/gjson"
@@ -431,24 +432,37 @@ func alignStoreDisabledPreviousResponseID(
 	return updated, true, nil
 }
 
-func cloneOpenAIWSPayloadBytes(payload []byte) []byte {
-	if len(payload) == 0 {
-		return nil
+// Replay 状态所有权不变式：replay 序列中的 json.RawMessage 正文一经放入即视为
+// 不可变，所有持有者共享同一份字节，任何修改都必须整体替换元素或重建 payload。
+// 序列头数组在跨持有者保存时必须新建（combineOpenAIWSReplayItems），禁止通过
+// 共享头 append，否则会写入其他持有者可见的底层数组。
+
+// combineOpenAIWSReplayItems 合并历史与增量为新头数组，正文共享不复制。
+func combineOpenAIWSReplayItems(history, delta []json.RawMessage) []json.RawMessage {
+	if len(delta) == 0 {
+		return history
 	}
-	cloned := make([]byte, len(payload))
-	copy(cloned, payload)
-	return cloned
+	combined := make([]json.RawMessage, 0, len(history)+len(delta))
+	combined = append(combined, history...)
+	return append(combined, delta...)
 }
 
-func cloneOpenAIWSRawMessages(items []json.RawMessage) []json.RawMessage {
-	if items == nil {
-		return nil
+// openAIWSPayloadStringView 返回与 payload 共享底层数组的零拷贝 string 视图，
+// 供 gjson.Get 使用（gjson.GetBytes 会整段复制结果 Raw，对 input 这类占
+// payload 主体的字段是每次 O(payload) 分配）。调用方必须保证 payload 在结果
+// 存活期间不可变（replay 所有权不变式）。
+func openAIWSPayloadStringView(payload []byte) string {
+	return unsafe.String(unsafe.SliceData(payload), len(payload))
+}
+
+// openAIWSRawMessageFromResult 优先返回 parent 的子切片（gjson 值零拷贝共享），
+// Index 不可用时回退为复制。共享要求 parent 遵守上面的不可变约定。
+func openAIWSRawMessageFromResult(parent []byte, value gjson.Result) json.RawMessage {
+	idx := value.Index
+	if idx > 0 && idx+len(value.Raw) <= len(parent) && string(parent[idx:idx+len(value.Raw)]) == value.Raw {
+		return json.RawMessage(parent[idx : idx+len(value.Raw)])
 	}
-	cloned := make([]json.RawMessage, 0, len(items))
-	for idx := range items {
-		cloned = append(cloned, json.RawMessage(cloneOpenAIWSPayloadBytes(items[idx])))
-	}
-	return cloned
+	return json.RawMessage(value.Raw)
 }
 
 func normalizeOpenAIWSJSONForCompare(raw []byte) ([]byte, error) {
@@ -495,30 +509,38 @@ func normalizeOpenAIWSPayloadWithoutInputAndPreviousResponseID(payload []byte) (
 	return json.Marshal(decoded)
 }
 
+// openAIWSExtractNormalizedInputSequence 拆出 input 序列。返回的正文尽可能与
+// payload 共享底层数组（零拷贝），受 replay 所有权不变式保护。
 func openAIWSExtractNormalizedInputSequence(payload []byte) ([]json.RawMessage, bool, error) {
 	if len(payload) == 0 {
 		return nil, false, nil
 	}
-	inputValue := gjson.GetBytes(payload, "input")
+	inputValue := gjson.Get(openAIWSPayloadStringView(payload), "input")
 	if !inputValue.Exists() {
 		return nil, false, nil
 	}
 	if inputValue.Type == gjson.JSON {
-		raw := strings.TrimSpace(inputValue.Raw)
-		if strings.HasPrefix(raw, "[") {
-			var items []json.RawMessage
-			if err := json.Unmarshal([]byte(raw), &items); err != nil {
-				return nil, true, err
+		if inputValue.IsArray() {
+			// gjson 宽容解析；数组整体先做零分配合法性校验，避免把断裂
+			// JSON 塞进 replay 历史。
+			arrayRaw := openAIWSRawMessageFromResult(payload, inputValue)
+			if !json.Valid(arrayRaw) {
+				return nil, true, errors.New("input array json is invalid")
+			}
+			elems := inputValue.Array()
+			items := make([]json.RawMessage, 0, len(elems))
+			for _, elem := range elems {
+				items = append(items, openAIWSRawMessageFromResult(payload, elem))
 			}
 			return items, true, nil
 		}
-		return []json.RawMessage{json.RawMessage(raw)}, true, nil
+		return []json.RawMessage{openAIWSRawMessageFromResult(payload, inputValue)}, true, nil
 	}
 	if inputValue.Type == gjson.String {
 		encoded, _ := json.Marshal(inputValue.String())
 		return []json.RawMessage{encoded}, true, nil
 	}
-	return []json.RawMessage{json.RawMessage(inputValue.Raw)}, true, nil
+	return []json.RawMessage{openAIWSRawMessageFromResult(payload, inputValue)}, true, nil
 }
 
 func openAIWSInputIsPrefixExtended(previousPayload, currentPayload []byte) (bool, error) {
@@ -561,6 +583,10 @@ func openAIWSRawItemsHasPrefix(items []json.RawMessage, prefix []json.RawMessage
 		return false
 	}
 	for idx := range prefix {
+		// 快路径：客户端逐字节重发历史时直接比较，避免整轮历史的解码/再编码。
+		if bytes.Equal(bytes.TrimSpace(prefix[idx]), bytes.TrimSpace(items[idx])) {
+			continue
+		}
 		previousNormalized := normalizeOpenAIWSJSONForCompareOrRaw(prefix[idx])
 		currentNormalized := normalizeOpenAIWSJSONForCompareOrRaw(items[idx])
 		if !bytes.Equal(previousNormalized, currentNormalized) {
@@ -611,12 +637,13 @@ func openAIWSRawItemsHaveToolCallContextForOutputs(items []json.RawMessage) bool
 	return true
 }
 
+// sanitizeOpenAIWSHistoricalReplayToolCalls 返回的新头数组与 previousItems 共享正文。
 func sanitizeOpenAIWSHistoricalReplayToolCalls(
 	previousItems []json.RawMessage,
 	currentItems []json.RawMessage,
 ) []json.RawMessage {
 	if len(previousItems) == 0 {
-		return cloneOpenAIWSRawMessages(previousItems)
+		return previousItems
 	}
 	outputCallIDs := make(map[string]struct{})
 	collectOutputCallIDs := func(items []json.RawMessage) {
@@ -640,7 +667,7 @@ func sanitizeOpenAIWSHistoricalReplayToolCalls(
 				continue
 			}
 		}
-		sanitized = append(sanitized, append(json.RawMessage(nil), item...))
+		sanitized = append(sanitized, item)
 	}
 	return sanitized
 }
@@ -649,7 +676,7 @@ func openAIWSRawPayloadHasToolCallOutput(payload []byte) bool {
 	if len(payload) == 0 {
 		return false
 	}
-	input := gjson.GetBytes(payload, "input")
+	input := gjson.Get(openAIWSPayloadStringView(payload), "input")
 	if !input.Exists() {
 		return false
 	}
@@ -667,6 +694,33 @@ func openAIWSRawPayloadHasToolCallOutput(payload []byte) bool {
 	return false
 }
 
+// buildOpenAIWSReplayInputSequenceFromItems 基于已解析的当前 turn input 构建
+// replay 序列。返回序列的正文与 previousFullInput/currentItems 共享所有权
+// （见 combineOpenAIWSReplayItems 上方的所有权不变式），头数组可能直接转移自
+// currentItems。
+func buildOpenAIWSReplayInputSequenceFromItems(
+	previousFullInput []json.RawMessage,
+	previousFullInputExists bool,
+	currentItems []json.RawMessage,
+	currentExists bool,
+	hasPreviousResponseID bool,
+) ([]json.RawMessage, bool) {
+	if !hasPreviousResponseID || !previousFullInputExists {
+		return currentItems, currentExists
+	}
+	previousFullInput = sanitizeOpenAIWSHistoricalReplayToolCalls(previousFullInput, currentItems)
+	if !currentExists || len(currentItems) == 0 {
+		return previousFullInput, true
+	}
+	if openAIWSRawItemsHasPrefix(currentItems, previousFullInput) {
+		return currentItems, true
+	}
+	merged := make([]json.RawMessage, 0, len(previousFullInput)+len(currentItems))
+	merged = append(merged, previousFullInput...)
+	merged = append(merged, currentItems...)
+	return merged, true
+}
+
 func buildOpenAIWSReplayInputSequence(
 	previousFullInput []json.RawMessage,
 	previousFullInputExists bool,
@@ -677,23 +731,14 @@ func buildOpenAIWSReplayInputSequence(
 	if currentErr != nil {
 		return nil, false, currentErr
 	}
-	if !hasPreviousResponseID {
-		return cloneOpenAIWSRawMessages(currentItems), currentExists, nil
-	}
-	if !previousFullInputExists {
-		return cloneOpenAIWSRawMessages(currentItems), currentExists, nil
-	}
-	previousFullInput = sanitizeOpenAIWSHistoricalReplayToolCalls(previousFullInput, currentItems)
-	if !currentExists || len(currentItems) == 0 {
-		return cloneOpenAIWSRawMessages(previousFullInput), true, nil
-	}
-	if openAIWSRawItemsHasPrefix(currentItems, previousFullInput) {
-		return cloneOpenAIWSRawMessages(currentItems), true, nil
-	}
-	merged := make([]json.RawMessage, 0, len(previousFullInput)+len(currentItems))
-	merged = append(merged, cloneOpenAIWSRawMessages(previousFullInput)...)
-	merged = append(merged, cloneOpenAIWSRawMessages(currentItems)...)
-	return merged, true, nil
+	items, exists := buildOpenAIWSReplayInputSequenceFromItems(
+		previousFullInput,
+		previousFullInputExists,
+		currentItems,
+		currentExists,
+		hasPreviousResponseID,
+	)
+	return items, exists, nil
 }
 
 func setOpenAIWSPayloadInputSequence(

backend/internal/service/openai_ws_http_bridge.go

@@ -8,6 +8,7 @@ import (
 	"fmt"
 	"io"
 	"net/http"
+	"slices"
 	"strings"
 	"time"
 
@@ -156,12 +157,14 @@ func (c *openAIWSToolCallReplayCollector) AddEvent(eventType string, message []b
 	}
 }
 
+// Items/AllItems 返回浅拷贝头数组；正文由 collector 独立分配且此后不可变，
+// 调用方按 replay 所有权不变式共享持有。
 func (c *openAIWSToolCallReplayCollector) Items() []json.RawMessage {
-	return cloneOpenAIWSRawMessages(c.items)
+	return slices.Clone(c.items)
 }
 
 func (c *openAIWSToolCallReplayCollector) AllItems() []json.RawMessage {
-	return cloneOpenAIWSRawMessages(c.allItems)
+	return slices.Clone(c.allItems)
 }
 
 func (c *openAIWSToolCallReplayCollector) addAllItem(item gjson.Result) {

backend/internal/service/openai_ws_replay_allocation_test.go

@@ -0,0 +1,80 @@
+package service
+
+import (
+	"encoding/json"
+	"fmt"
+	"runtime"
+	"strings"
+	"testing"
+
+	"github.com/stretchr/testify/require"
+)
+
+// buildReplayTurnPayload 构造第 turn 轮的全量重发 payload：客户端历史逐轮追加
+// itemBytes 大小的项（Codex store=false 模式的真实形态）。
+func buildReplayTurnPayload(turn, itemBytes int) []byte {
+	var b strings.Builder
+	_, _ = b.WriteString(`{"type":"response.create","model":"gpt-5.5","stream":true,"input":[`)
+	filler := strings.Repeat("x", itemBytes)
+	for i := 1; i <= turn; i++ {
+		if i > 1 {
+			_, _ = b.WriteString(",")
+		}
+		_, _ = fmt.Fprintf(&b, `{"type":"input_text","text":"turn-%d-%s"}`, i, filler)
+	}
+	_, _ = b.WriteString(`]}`)
+	return []byte(b.String())
+}
+
+// TestOpenAIWSReplayStateBuildAllocationBounded 长会话分配回归：128 turn、每轮
+// ~10KiB 增量，全量历史逐轮重发。replay 状态构建（build + 历史保存）必须共享
+// 正文而非逐轮深拷贝，否则累计分配为 O(T²)（本场景 >160MB）；共享实现的累计
+// 分配与客户端重发总量同阶（~85MB payload 本身之外仅头数组与解析开销）。
+func TestOpenAIWSReplayStateBuildAllocationBounded(t *testing.T) {
+	const (
+		turns     = 128
+		itemBytes = 10 * 1024
+	)
+
+	payloads := make([][]byte, 0, turns)
+	for turn := 1; turn <= turns; turn++ {
+		payloads = append(payloads, buildReplayTurnPayload(turn, itemBytes))
+	}
+
+	var history []json.RawMessage
+	historyExists := false
+	delta := []json.RawMessage{json.RawMessage(`{"type":"function_call","id":"item_1","call_id":"call_1","name":"exec","arguments":"{}"}`)}
+
+	runtime.GC()
+	var before runtime.MemStats
+	runtime.ReadMemStats(&before)
+
+	for turn := 1; turn <= turns; turn++ {
+		items, exists, err := buildOpenAIWSReplayInputSequence(history, historyExists, payloads[turn-1], turn > 1)
+		require.NoError(t, err)
+		require.True(t, exists)
+		require.Len(t, items, turn)
+		// 保存历史 + collector 增量合并（与 ingress/bridge 保存点同构）。
+		history = combineOpenAIWSReplayItems(items, delta)
+		historyExists = true
+		// 下一轮 payload 含全部用户项但不含 collector 项，触发 sanitize+merge 路径中
+		// 最常见的 prefix 分支比较。
+		history = history[:len(history)-1]
+	}
+
+	var after runtime.MemStats
+	runtime.ReadMemStats(&after)
+	allocated := after.TotalAlloc - before.TotalAlloc
+
+	// 正文共享实现全程约 2.5MB（头数组与 gjson 解析开销）。任何逐轮 O(H) 的
+	// 字节级复制（extract 拷贝、正文 clone、保存点深拷贝）都会叠加 ≥84MB
+	// （sum(t×10KiB)）的量级，直接击穿此上界。
+	const maxAllocatedBytes = 32 * 1024 * 1024
+	require.Lessf(
+		t,
+		allocated,
+		uint64(maxAllocatedBytes),
+		"replay 状态构建累计分配 %d bytes 超出上界，疑似回归为逐轮深拷贝",
+		allocated,
+	)
+}