diff --git a/README_CN.md b/README_CN.md
index b8a818b3..41d399d5 100644
--- a/README_CN.md
+++ b/README_CN.md
@@ -57,6 +57,13 @@ Sub2API 是一个 AI API 网关平台，用于分发和管理 AI 产品订阅（
 
 ---
 
+## OpenAI Responses 兼容注意事项
+
+- 当请求包含 `function_call_output` 时，需要携带 `previous_response_id`，或在 `input` 中包含带 `call_id` 的 `tool_call`/`function_call`，或带非空 `id` 且与 `function_call_output.call_id` 匹配的 `item_reference`。
+- 若依赖上游历史记录，网关会强制 `store=true` 并需要复用 `previous_response_id`，以避免出现 “No tool call found for function call output” 错误。
+
+---
+
 ## 部署方式
 
 ### 方式一：脚本安装（推荐）
diff --git a/backend/internal/handler/openai_gateway_handler.go b/backend/internal/handler/openai_gateway_handler.go
index 3011b97d..c4cfabc3 100644
--- a/backend/internal/handler/openai_gateway_handler.go
+++ b/backend/internal/handler/openai_gateway_handler.go
@@ -114,6 +114,26 @@ func (h *OpenAIGatewayHandler) Responses(c *gin.Context) {
 
 	setOpsRequestContext(c, reqModel, reqStream, body)
 
+	// 提前校验 function_call_output 是否具备可关联上下文，避免上游 400。
+	// 要求 previous_response_id，或 input 内存在带 call_id 的 tool_call/function_call，
+	// 或带 id 且与 call_id 匹配的 item_reference。
+	if service.HasFunctionCallOutput(reqBody) {
+		previousResponseID, _ := reqBody["previous_response_id"].(string)
+		if strings.TrimSpace(previousResponseID) == "" && !service.HasToolCallContext(reqBody) {
+			if service.HasFunctionCallOutputMissingCallID(reqBody) {
+				log.Printf("[OpenAI Handler] function_call_output 缺少 call_id: model=%s", reqModel)
+				h.errorResponse(c, http.StatusBadRequest, "invalid_request_error", "function_call_output requires call_id or previous_response_id; if relying on history, ensure store=true and reuse previous_response_id")
+				return
+			}
+			callIDs := service.FunctionCallOutputCallIDs(reqBody)
+			if !service.HasItemReferenceForCallIDs(reqBody, callIDs) {
+				log.Printf("[OpenAI Handler] function_call_output 缺少匹配的 item_reference: model=%s", reqModel)
+				h.errorResponse(c, http.StatusBadRequest, "invalid_request_error", "function_call_output requires item_reference ids matching each call_id, or previous_response_id/tool_call context; if relying on history, ensure store=true and reuse previous_response_id")
+				return
+			}
+		}
+	}
+
 	// Track if we've started streaming (for error handling)
 	streamStarted := false
 
diff --git a/backend/internal/middleware/rate_limiter.go b/backend/internal/middleware/rate_limiter.go
index 13b71683..819d74c2 100644
--- a/backend/internal/middleware/rate_limiter.go
+++ b/backend/internal/middleware/rate_limiter.go
@@ -2,7 +2,10 @@ package middleware
 
 import (
 	"context"
+	"fmt"
+	"log"
 	"net/http"
+	"strconv"
 	"time"
 
 	"github.com/gin-gonic/gin"
@@ -25,15 +28,34 @@ type RateLimitOptions struct {
 var rateLimitScript = redis.NewScript(`
 local current = redis.call('INCR', KEYS[1])
 local ttl = redis.call('PTTL', KEYS[1])
-if current == 1 or ttl == -1 then
+local repaired = 0
+if current == 1 then
   redis.call('PEXPIRE', KEYS[1], ARGV[1])
+elseif ttl == -1 then
+  redis.call('PEXPIRE', KEYS[1], ARGV[1])
+  repaired = 1
 end
-return current
+return {current, repaired}
 `)
 
 // rateLimitRun 允许测试覆写脚本执行逻辑
-var rateLimitRun = func(ctx context.Context, client *redis.Client, key string, windowMillis int64) (int64, error) {
-	return rateLimitScript.Run(ctx, client, []string{key}, windowMillis).Int64()
+var rateLimitRun = func(ctx context.Context, client *redis.Client, key string, windowMillis int64) (int64, bool, error) {
+	values, err := rateLimitScript.Run(ctx, client, []string{key}, windowMillis).Slice()
+	if err != nil {
+		return 0, false, err
+	}
+	if len(values) < 2 {
+		return 0, false, fmt.Errorf("rate limit script returned %d values", len(values))
+	}
+	count, err := parseInt64(values[0])
+	if err != nil {
+		return 0, false, err
+	}
+	repaired, err := parseInt64(values[1])
+	if err != nil {
+		return 0, false, err
+	}
+	return count, repaired == 1, nil
 }
 
 // RateLimiter Redis 速率限制器
@@ -74,8 +96,9 @@ func (r *RateLimiter) LimitWithOptions(key string, limit int, window time.Durati
 		windowMillis := windowTTLMillis(window)
 
 		// 使用 Lua 脚本原子操作增加计数并设置过期
-		count, err := rateLimitRun(ctx, r.redis, redisKey, windowMillis)
+		count, repaired, err := rateLimitRun(ctx, r.redis, redisKey, windowMillis)
 		if err != nil {
+			log.Printf("[RateLimit] redis error: key=%s mode=%s err=%v", redisKey, failureModeLabel(failureMode), err)
 			if failureMode == RateLimitFailClose {
 				abortRateLimit(c)
 				return
@@ -84,6 +107,9 @@ func (r *RateLimiter) LimitWithOptions(key string, limit int, window time.Durati
 			c.Next()
 			return
 		}
+		if repaired {
+			log.Printf("[RateLimit] ttl repaired: key=%s window_ms=%d", redisKey, windowMillis)
+		}
 
 		// 超过限制
 		if count > int64(limit) {
@@ -109,3 +135,27 @@ func abortRateLimit(c *gin.Context) {
 		"message": "Too many requests, please try again later",
 	})
 }
+
+func failureModeLabel(mode RateLimitFailureMode) string {
+	if mode == RateLimitFailClose {
+		return "fail-close"
+	}
+	return "fail-open"
+}
+
+func parseInt64(value any) (int64, error) {
+	switch v := value.(type) {
+	case int64:
+		return v, nil
+	case int:
+		return int64(v), nil
+	case string:
+		parsed, err := strconv.ParseInt(v, 10, 64)
+		if err != nil {
+			return 0, err
+		}
+		return parsed, nil
+	default:
+		return 0, fmt.Errorf("unexpected value type %T", value)
+	}
+}
diff --git a/backend/internal/middleware/rate_limiter_test.go b/backend/internal/middleware/rate_limiter_test.go
index 7c72e5be..0c379c0f 100644
--- a/backend/internal/middleware/rate_limiter_test.go
+++ b/backend/internal/middleware/rate_limiter_test.go
@@ -66,13 +66,13 @@ func TestRateLimiterSuccessAndLimit(t *testing.T) {
 	originalRun := rateLimitRun
 	counts := []int64{1, 2}
 	callIndex := 0
-	rateLimitRun = func(ctx context.Context, client *redis.Client, key string, windowMillis int64) (int64, error) {
+	rateLimitRun = func(ctx context.Context, client *redis.Client, key string, windowMillis int64) (int64, bool, error) {
 		if callIndex >= len(counts) {
-			return counts[len(counts)-1], nil
+			return counts[len(counts)-1], false, nil
 		}
 		value := counts[callIndex]
 		callIndex++
-		return value, nil
+		return value, false, nil
 	}
 	t.Cleanup(func() {
 		rateLimitRun = originalRun
diff --git a/backend/internal/service/openai_codex_transform.go b/backend/internal/service/openai_codex_transform.go
index 97b405b2..dcc30fc1 100644
--- a/backend/internal/service/openai_codex_transform.go
+++ b/backend/internal/service/openai_codex_transform.go
@@ -74,6 +74,8 @@ type opencodeCacheMetadata struct {
 
 func applyCodexOAuthTransform(reqBody map[string]any) codexTransformResult {
 	result := codexTransformResult{}
+	// 工具续链需求会影响存储策略与 input 过滤逻辑。
+	needsToolContinuation := NeedsToolContinuation(reqBody)
 
 	model := ""
 	if v, ok := reqBody["model"].(string); ok {
@@ -88,9 +90,17 @@ func applyCodexOAuthTransform(reqBody map[string]any) codexTransformResult {
 		result.NormalizedModel = normalizedModel
 	}
 
-	if v, ok := reqBody["store"].(bool); !ok || v {
-		reqBody["store"] = false
-		result.Modified = true
+	// 续链场景强制启用 store；非续链仍按原策略强制关闭存储。
+	if needsToolContinuation {
+		if v, ok := reqBody["store"].(bool); !ok || !v {
+			reqBody["store"] = true
+			result.Modified = true
+		}
+	} else {
+		if v, ok := reqBody["store"].(bool); !ok || v {
+			reqBody["store"] = false
+			result.Modified = true
+		}
 	}
 	if v, ok := reqBody["stream"].(bool); !ok || !v {
 		reqBody["stream"] = true
@@ -124,7 +134,7 @@ func applyCodexOAuthTransform(reqBody map[string]any) codexTransformResult {
 			result.Modified = true
 		}
 	} else if existingInstructions == "" {
-		// If no opencode instructions available, try codex CLI instructions
+		// 未获取到 opencode 指令时，回退使用 Codex CLI 指令。
 		codexInstructions := strings.TrimSpace(getCodexCLIInstructions())
 		if codexInstructions != "" {
 			reqBody["instructions"] = codexInstructions
@@ -132,8 +142,9 @@ func applyCodexOAuthTransform(reqBody map[string]any) codexTransformResult {
 		}
 	}
 
+	// 续链场景保留 item_reference 与 id，避免 call_id 上下文丢失。
 	if input, ok := reqBody["input"].([]any); ok {
-		input = filterCodexInput(input)
+		input = filterCodexInput(input, needsToolContinuation)
 		reqBody["input"] = input
 		result.Modified = true
 	}
@@ -246,15 +257,15 @@ func getOpenCodeCachedPrompt(url, cacheFileName, metaFileName string) string {
 }
 
 func getOpenCodeCodexHeader() string {
-	// Try to get from opencode repository first
+	// 优先从 opencode 仓库缓存获取指令。
 	opencodeInstructions := getOpenCodeCachedPrompt(opencodeCodexHeaderURL, "opencode-codex-header.txt", "opencode-codex-header-meta.json")
 
-	// If opencode instructions are available, return them
+	// 若 opencode 指令可用，直接返回。
 	if opencodeInstructions != "" {
 		return opencodeInstructions
 	}
 
-	// Fallback to local codex CLI instructions
+	// 否则回退使用本地 Codex CLI 指令。
 	return getCodexCLIInstructions()
 }
 
@@ -266,10 +277,12 @@ func GetOpenCodeInstructions() string {
 	return getOpenCodeCodexHeader()
 }
 
+// GetCodexCLIInstructions 返回内置的 Codex CLI 指令内容。
 func GetCodexCLIInstructions() string {
 	return getCodexCLIInstructions()
 }
 
+// ReplaceWithCodexInstructions 将请求 instructions 替换为内置 Codex 指令（必要时）。
 func ReplaceWithCodexInstructions(reqBody map[string]any) bool {
 	codexInstructions := strings.TrimSpace(getCodexCLIInstructions())
 	if codexInstructions == "" {
@@ -285,6 +298,7 @@ func ReplaceWithCodexInstructions(reqBody map[string]any) bool {
 	return false
 }
 
+// IsInstructionError 判断错误信息是否与指令格式/系统提示相关。
 func IsInstructionError(errorMessage string) bool {
 	if errorMessage == "" {
 		return false
@@ -309,7 +323,9 @@ func IsInstructionError(errorMessage string) bool {
 	return false
 }
 
-func filterCodexInput(input []any) []any {
+// filterCodexInput 按需过滤 item_reference 与 id。
+// preserveReferences 为 true 时保持引用与 id，以满足续链请求对上下文的依赖。
+func filterCodexInput(input []any, preserveReferences bool) []any {
 	filtered := make([]any, 0, len(input))
 	for _, item := range input {
 		m, ok := item.(map[string]any)
@@ -319,23 +335,49 @@ func filterCodexInput(input []any) []any {
 		}
 		typ, _ := m["type"].(string)
 		if typ == "item_reference" {
-			filtered = append(filtered, m)
+			if !preserveReferences {
+				continue
+			}
+			newItem := make(map[string]any, len(m))
+			for key, value := range m {
+				newItem[key] = value
+			}
+			filtered = append(filtered, newItem)
 			continue
 		}
-		// Strip per-item ids; keep call_id only for tool call items so outputs can match.
+
+		newItem := m
+		copied := false
+		// 仅在需要修改字段时创建副本，避免直接改写原始输入。
+		ensureCopy := func() {
+			if copied {
+				return
+			}
+			newItem = make(map[string]any, len(m))
+			for key, value := range m {
+				newItem[key] = value
+			}
+			copied = true
+		}
+
 		if isCodexToolCallItemType(typ) {
-			callID, _ := m["call_id"].(string)
-			if strings.TrimSpace(callID) == "" {
+			if callID, ok := m["call_id"].(string); !ok || strings.TrimSpace(callID) == "" {
 				if id, ok := m["id"].(string); ok && strings.TrimSpace(id) != "" {
-					m["call_id"] = id
+					ensureCopy()
+					newItem["call_id"] = id
 				}
 			}
 		}
-		delete(m, "id")
-		if !isCodexToolCallItemType(typ) {
-			delete(m, "call_id")
+
+		if !preserveReferences {
+			ensureCopy()
+			delete(newItem, "id")
+			if !isCodexToolCallItemType(typ) {
+				delete(newItem, "call_id")
+			}
 		}
-		filtered = append(filtered, m)
+
+		filtered = append(filtered, newItem)
 	}
 	return filtered
 }
diff --git a/backend/internal/service/openai_codex_transform_test.go b/backend/internal/service/openai_codex_transform_test.go
new file mode 100644
index 00000000..9663229f
--- /dev/null
+++ b/backend/internal/service/openai_codex_transform_test.go
@@ -0,0 +1,147 @@
+package service
+
+import (
+	"encoding/json"
+	"os"
+	"path/filepath"
+	"testing"
+	"time"
+
+	"github.com/stretchr/testify/require"
+)
+
+func TestApplyCodexOAuthTransform_ToolContinuationPreservesInput(t *testing.T) {
+	// 续链场景：保留 item_reference 与 id，并启用 store。
+	setupCodexCache(t)
+
+	reqBody := map[string]any{
+		"model": "gpt-5.2",
+		"input": []any{
+			map[string]any{"type": "item_reference", "id": "ref1", "text": "x"},
+			map[string]any{"type": "function_call_output", "call_id": "call_1", "output": "ok", "id": "o1"},
+		},
+		"tool_choice": "auto",
+	}
+
+	applyCodexOAuthTransform(reqBody)
+
+	store, ok := reqBody["store"].(bool)
+	require.True(t, ok)
+	require.True(t, store)
+
+	input, ok := reqBody["input"].([]any)
+	require.True(t, ok)
+	require.Len(t, input, 2)
+
+	// 校验 input[0] 为 map，避免断言失败导致测试中断。
+	first, ok := input[0].(map[string]any)
+	require.True(t, ok)
+	require.Equal(t, "item_reference", first["type"])
+	require.Equal(t, "ref1", first["id"])
+
+	// 校验 input[1] 为 map，确保后续字段断言安全。
+	second, ok := input[1].(map[string]any)
+	require.True(t, ok)
+	require.Equal(t, "o1", second["id"])
+}
+
+func TestApplyCodexOAuthTransform_ToolContinuationForcesStoreTrue(t *testing.T) {
+	// 续链场景：显式 store=false 也会被强制为 true。
+	setupCodexCache(t)
+
+	reqBody := map[string]any{
+		"model": "gpt-5.1",
+		"store": false,
+		"input": []any{
+			map[string]any{"type": "function_call_output", "call_id": "call_1"},
+		},
+		"tool_choice": "auto",
+	}
+
+	applyCodexOAuthTransform(reqBody)
+
+	store, ok := reqBody["store"].(bool)
+	require.True(t, ok)
+	require.True(t, store)
+}
+
+func TestApplyCodexOAuthTransform_NonContinuationForcesStoreFalseAndStripsIDs(t *testing.T) {
+	// 非续链场景：强制 store=false，并移除 input 中的 id。
+	setupCodexCache(t)
+
+	reqBody := map[string]any{
+		"model": "gpt-5.1",
+		"store": true,
+		"input": []any{
+			map[string]any{"type": "text", "id": "t1", "text": "hi"},
+		},
+	}
+
+	applyCodexOAuthTransform(reqBody)
+
+	store, ok := reqBody["store"].(bool)
+	require.True(t, ok)
+	require.False(t, store)
+
+	input, ok := reqBody["input"].([]any)
+	require.True(t, ok)
+	require.Len(t, input, 1)
+	// 校验 input[0] 为 map，避免类型不匹配触发 errcheck。
+	item, ok := input[0].(map[string]any)
+	require.True(t, ok)
+	_, hasID := item["id"]
+	require.False(t, hasID)
+}
+
+func TestFilterCodexInput_RemovesItemReferenceWhenNotPreserved(t *testing.T) {
+	input := []any{
+		map[string]any{"type": "item_reference", "id": "ref1"},
+		map[string]any{"type": "text", "id": "t1", "text": "hi"},
+	}
+
+	filtered := filterCodexInput(input, false)
+	require.Len(t, filtered, 1)
+	// 校验 filtered[0] 为 map，确保字段检查可靠。
+	item, ok := filtered[0].(map[string]any)
+	require.True(t, ok)
+	require.Equal(t, "text", item["type"])
+	_, hasID := item["id"]
+	require.False(t, hasID)
+}
+
+func TestApplyCodexOAuthTransform_EmptyInput(t *testing.T) {
+	// 空 input 应保持为空且不触发异常。
+	setupCodexCache(t)
+
+	reqBody := map[string]any{
+		"model": "gpt-5.1",
+		"input": []any{},
+	}
+
+	applyCodexOAuthTransform(reqBody)
+
+	input, ok := reqBody["input"].([]any)
+	require.True(t, ok)
+	require.Len(t, input, 0)
+}
+
+func setupCodexCache(t *testing.T) {
+	t.Helper()
+
+	// 使用临时 HOME 避免触发网络拉取 header。
+	tempDir := t.TempDir()
+	t.Setenv("HOME", tempDir)
+
+	cacheDir := filepath.Join(tempDir, ".opencode", "cache")
+	require.NoError(t, os.MkdirAll(cacheDir, 0o755))
+	require.NoError(t, os.WriteFile(filepath.Join(cacheDir, "opencode-codex-header.txt"), []byte("header"), 0o644))
+
+	meta := map[string]any{
+		"etag":        "",
+		"lastFetch":   time.Now().UTC().Format(time.RFC3339),
+		"lastChecked": time.Now().UnixMilli(),
+	}
+	data, err := json.Marshal(meta)
+	require.NoError(t, err)
+	require.NoError(t, os.WriteFile(filepath.Join(cacheDir, "opencode-codex-header-meta.json"), data, 0o644))
+}
diff --git a/backend/internal/service/openai_gateway_service.go b/backend/internal/service/openai_gateway_service.go
index ffd42d2f..bac117b8 100644
--- a/backend/internal/service/openai_gateway_service.go
+++ b/backend/internal/service/openai_gateway_service.go
@@ -546,7 +546,7 @@ func (s *OpenAIGatewayService) Forward(ctx context.Context, c *gin.Context, acco
 
 	isCodexCLI := openai.IsCodexCLIRequest(c.GetHeader("User-Agent"))
 
-	// Apply model mapping for all requests (including Codex CLI)
+	// 对所有请求执行模型映射（包含 Codex CLI）。
 	mappedModel := account.GetMappedModel(reqModel)
 	if mappedModel != reqModel {
 		log.Printf("[OpenAI] Model mapping applied: %s -> %s (account: %s, isCodexCLI: %v)", reqModel, mappedModel, account.Name, isCodexCLI)
@@ -554,7 +554,7 @@ func (s *OpenAIGatewayService) Forward(ctx context.Context, c *gin.Context, acco
 		bodyModified = true
 	}
 
-	// Apply Codex model normalization for all OpenAI accounts
+	// 针对所有 OpenAI 账号执行 Codex 模型名规范化，确保上游识别一致。
 	if model, ok := reqBody["model"].(string); ok {
 		normalizedModel := normalizeCodexModel(model)
 		if normalizedModel != "" && normalizedModel != model {
@@ -566,7 +566,7 @@ func (s *OpenAIGatewayService) Forward(ctx context.Context, c *gin.Context, acco
 		}
 	}
 
-	// Normalize reasoning.effort parameter (minimal -> none)
+	// 规范化 reasoning.effort 参数（minimal -> none），与上游允许值对齐。
 	if reasoning, ok := reqBody["reasoning"].(map[string]any); ok {
 		if effort, ok := reasoning["effort"].(string); ok && effort == "minimal" {
 			reasoning["effort"] = "none"
diff --git a/backend/internal/service/openai_tool_continuation.go b/backend/internal/service/openai_tool_continuation.go
new file mode 100644
index 00000000..e59082b2
--- /dev/null
+++ b/backend/internal/service/openai_tool_continuation.go
@@ -0,0 +1,213 @@
+package service
+
+import "strings"
+
+// NeedsToolContinuation 判定请求是否需要工具调用续链处理。
+// 满足以下任一信号即视为续链：previous_response_id、input 内包含 function_call_output/item_reference、
+// 或显式声明 tools/tool_choice。
+func NeedsToolContinuation(reqBody map[string]any) bool {
+	if reqBody == nil {
+		return false
+	}
+	if hasNonEmptyString(reqBody["previous_response_id"]) {
+		return true
+	}
+	if hasToolsSignal(reqBody) {
+		return true
+	}
+	if hasToolChoiceSignal(reqBody) {
+		return true
+	}
+	if inputHasType(reqBody, "function_call_output") {
+		return true
+	}
+	if inputHasType(reqBody, "item_reference") {
+		return true
+	}
+	return false
+}
+
+// HasFunctionCallOutput 判断 input 是否包含 function_call_output，用于触发续链校验。
+func HasFunctionCallOutput(reqBody map[string]any) bool {
+	if reqBody == nil {
+		return false
+	}
+	return inputHasType(reqBody, "function_call_output")
+}
+
+// HasToolCallContext 判断 input 是否包含带 call_id 的 tool_call/function_call，
+// 用于判断 function_call_output 是否具备可关联的上下文。
+func HasToolCallContext(reqBody map[string]any) bool {
+	if reqBody == nil {
+		return false
+	}
+	input, ok := reqBody["input"].([]any)
+	if !ok {
+		return false
+	}
+	for _, item := range input {
+		itemMap, ok := item.(map[string]any)
+		if !ok {
+			continue
+		}
+		itemType, _ := itemMap["type"].(string)
+		if itemType != "tool_call" && itemType != "function_call" {
+			continue
+		}
+		if callID, ok := itemMap["call_id"].(string); ok && strings.TrimSpace(callID) != "" {
+			return true
+		}
+	}
+	return false
+}
+
+// FunctionCallOutputCallIDs 提取 input 中 function_call_output 的 call_id 集合。
+// 仅返回非空 call_id，用于与 item_reference.id 做匹配校验。
+func FunctionCallOutputCallIDs(reqBody map[string]any) []string {
+	if reqBody == nil {
+		return nil
+	}
+	input, ok := reqBody["input"].([]any)
+	if !ok {
+		return nil
+	}
+	ids := make(map[string]struct{})
+	for _, item := range input {
+		itemMap, ok := item.(map[string]any)
+		if !ok {
+			continue
+		}
+		itemType, _ := itemMap["type"].(string)
+		if itemType != "function_call_output" {
+			continue
+		}
+		if callID, ok := itemMap["call_id"].(string); ok && strings.TrimSpace(callID) != "" {
+			ids[callID] = struct{}{}
+		}
+	}
+	if len(ids) == 0 {
+		return nil
+	}
+	result := make([]string, 0, len(ids))
+	for id := range ids {
+		result = append(result, id)
+	}
+	return result
+}
+
+// HasFunctionCallOutputMissingCallID 判断是否存在缺少 call_id 的 function_call_output。
+func HasFunctionCallOutputMissingCallID(reqBody map[string]any) bool {
+	if reqBody == nil {
+		return false
+	}
+	input, ok := reqBody["input"].([]any)
+	if !ok {
+		return false
+	}
+	for _, item := range input {
+		itemMap, ok := item.(map[string]any)
+		if !ok {
+			continue
+		}
+		itemType, _ := itemMap["type"].(string)
+		if itemType != "function_call_output" {
+			continue
+		}
+		callID, _ := itemMap["call_id"].(string)
+		if strings.TrimSpace(callID) == "" {
+			return true
+		}
+	}
+	return false
+}
+
+// HasItemReferenceForCallIDs 判断 item_reference.id 是否覆盖所有 call_id。
+// 用于仅依赖引用项完成续链场景的校验。
+func HasItemReferenceForCallIDs(reqBody map[string]any, callIDs []string) bool {
+	if reqBody == nil || len(callIDs) == 0 {
+		return false
+	}
+	input, ok := reqBody["input"].([]any)
+	if !ok {
+		return false
+	}
+	referenceIDs := make(map[string]struct{})
+	for _, item := range input {
+		itemMap, ok := item.(map[string]any)
+		if !ok {
+			continue
+		}
+		itemType, _ := itemMap["type"].(string)
+		if itemType != "item_reference" {
+			continue
+		}
+		idValue, _ := itemMap["id"].(string)
+		idValue = strings.TrimSpace(idValue)
+		if idValue == "" {
+			continue
+		}
+		referenceIDs[idValue] = struct{}{}
+	}
+	if len(referenceIDs) == 0 {
+		return false
+	}
+	for _, callID := range callIDs {
+		if _, ok := referenceIDs[callID]; !ok {
+			return false
+		}
+	}
+	return true
+}
+
+// inputHasType 判断 input 中是否存在指定类型的 item。
+func inputHasType(reqBody map[string]any, want string) bool {
+	input, ok := reqBody["input"].([]any)
+	if !ok {
+		return false
+	}
+	for _, item := range input {
+		itemMap, ok := item.(map[string]any)
+		if !ok {
+			continue
+		}
+		itemType, _ := itemMap["type"].(string)
+		if itemType == want {
+			return true
+		}
+	}
+	return false
+}
+
+// hasNonEmptyString 判断字段是否为非空字符串。
+func hasNonEmptyString(value any) bool {
+	stringValue, ok := value.(string)
+	return ok && strings.TrimSpace(stringValue) != ""
+}
+
+// hasToolsSignal 判断 tools 字段是否显式声明（存在且不为空）。
+func hasToolsSignal(reqBody map[string]any) bool {
+	raw, exists := reqBody["tools"]
+	if !exists || raw == nil {
+		return false
+	}
+	if tools, ok := raw.([]any); ok {
+		return len(tools) > 0
+	}
+	return false
+}
+
+// hasToolChoiceSignal 判断 tool_choice 是否显式声明（非空或非 nil）。
+func hasToolChoiceSignal(reqBody map[string]any) bool {
+	raw, exists := reqBody["tool_choice"]
+	if !exists || raw == nil {
+		return false
+	}
+	switch value := raw.(type) {
+	case string:
+		return strings.TrimSpace(value) != ""
+	case map[string]any:
+		return len(value) > 0
+	default:
+		return false
+	}
+}
diff --git a/backend/internal/service/openai_tool_continuation_test.go b/backend/internal/service/openai_tool_continuation_test.go
new file mode 100644
index 00000000..fe737ad6
--- /dev/null
+++ b/backend/internal/service/openai_tool_continuation_test.go
@@ -0,0 +1,98 @@
+package service
+
+import (
+	"testing"
+
+	"github.com/stretchr/testify/require"
+)
+
+func TestNeedsToolContinuationSignals(t *testing.T) {
+	// 覆盖所有触发续链的信号来源，确保判定逻辑完整。
+	cases := []struct {
+		name string
+		body map[string]any
+		want bool
+	}{
+		{name: "nil", body: nil, want: false},
+		{name: "previous_response_id", body: map[string]any{"previous_response_id": "resp_1"}, want: true},
+		{name: "previous_response_id_blank", body: map[string]any{"previous_response_id": "  "}, want: false},
+		{name: "function_call_output", body: map[string]any{"input": []any{map[string]any{"type": "function_call_output"}}}, want: true},
+		{name: "item_reference", body: map[string]any{"input": []any{map[string]any{"type": "item_reference"}}}, want: true},
+		{name: "tools", body: map[string]any{"tools": []any{map[string]any{"type": "function"}}}, want: true},
+		{name: "tools_empty", body: map[string]any{"tools": []any{}}, want: false},
+		{name: "tools_invalid", body: map[string]any{"tools": "bad"}, want: false},
+		{name: "tool_choice", body: map[string]any{"tool_choice": "auto"}, want: true},
+		{name: "tool_choice_object", body: map[string]any{"tool_choice": map[string]any{"type": "function"}}, want: true},
+		{name: "tool_choice_empty_object", body: map[string]any{"tool_choice": map[string]any{}}, want: false},
+		{name: "none", body: map[string]any{"input": []any{map[string]any{"type": "text", "text": "hi"}}}, want: false},
+	}
+
+	for _, tt := range cases {
+		t.Run(tt.name, func(t *testing.T) {
+			require.Equal(t, tt.want, NeedsToolContinuation(tt.body))
+		})
+	}
+}
+
+func TestHasFunctionCallOutput(t *testing.T) {
+	// 仅当 input 中存在 function_call_output 才视为续链输出。
+	require.False(t, HasFunctionCallOutput(nil))
+	require.True(t, HasFunctionCallOutput(map[string]any{
+		"input": []any{map[string]any{"type": "function_call_output"}},
+	}))
+	require.False(t, HasFunctionCallOutput(map[string]any{
+		"input": "text",
+	}))
+}
+
+func TestHasToolCallContext(t *testing.T) {
+	// tool_call/function_call 必须包含 call_id，才能作为可关联上下文。
+	require.False(t, HasToolCallContext(nil))
+	require.True(t, HasToolCallContext(map[string]any{
+		"input": []any{map[string]any{"type": "tool_call", "call_id": "call_1"}},
+	}))
+	require.True(t, HasToolCallContext(map[string]any{
+		"input": []any{map[string]any{"type": "function_call", "call_id": "call_2"}},
+	}))
+	require.False(t, HasToolCallContext(map[string]any{
+		"input": []any{map[string]any{"type": "tool_call"}},
+	}))
+}
+
+func TestFunctionCallOutputCallIDs(t *testing.T) {
+	// 仅提取非空 call_id，去重后返回。
+	require.Empty(t, FunctionCallOutputCallIDs(nil))
+	callIDs := FunctionCallOutputCallIDs(map[string]any{
+		"input": []any{
+			map[string]any{"type": "function_call_output", "call_id": "call_1"},
+			map[string]any{"type": "function_call_output", "call_id": ""},
+			map[string]any{"type": "function_call_output", "call_id": "call_1"},
+		},
+	})
+	require.ElementsMatch(t, []string{"call_1"}, callIDs)
+}
+
+func TestHasFunctionCallOutputMissingCallID(t *testing.T) {
+	require.False(t, HasFunctionCallOutputMissingCallID(nil))
+	require.True(t, HasFunctionCallOutputMissingCallID(map[string]any{
+		"input": []any{map[string]any{"type": "function_call_output"}},
+	}))
+	require.False(t, HasFunctionCallOutputMissingCallID(map[string]any{
+		"input": []any{map[string]any{"type": "function_call_output", "call_id": "call_1"}},
+	}))
+}
+
+func TestHasItemReferenceForCallIDs(t *testing.T) {
+	// item_reference 需要覆盖所有 call_id 才视为可关联上下文。
+	require.False(t, HasItemReferenceForCallIDs(nil, []string{"call_1"}))
+	require.False(t, HasItemReferenceForCallIDs(map[string]any{}, []string{"call_1"}))
+	req := map[string]any{
+		"input": []any{
+			map[string]any{"type": "item_reference", "id": "call_1"},
+			map[string]any{"type": "item_reference", "id": "call_2"},
+		},
+	}
+	require.True(t, HasItemReferenceForCallIDs(req, []string{"call_1"}))
+	require.True(t, HasItemReferenceForCallIDs(req, []string{"call_1", "call_2"}))
+	require.False(t, HasItemReferenceForCallIDs(req, []string{"call_1", "call_3"}))
+}