fix(openai): 增强 OpenCode 兼容性和模型规范化

## 主要改动

1. **模型规范化扩展到所有账号**
   - 将 Codex 模型规范化（如 gpt-5-nano → gpt-5.1）应用到所有 OpenAI 账号类型
   - 不再仅限于 OAuth 非 CLI 请求
   - 解决 Codex CLI 使用 ChatGPT 账号时的模型兼容性问题

2. **reasoning.effort 参数规范化**
   - 自动将 `minimal` 转换为 `none`
   - 解决 gpt-5.1 模型不支持 `minimal` 值的问题

3. **Session/Conversation ID fallback 机制**
   - 从请求体多个字段提取 session_id/conversation_id
   - 优先级：prompt_cache_key → session_id → conversation_id → previous_response_id
   - 支持 Codex CLI 的会话保持

4. **Tool Call ID fallback**
   - 当 call_id 为空时使用 id 字段作为 fallback
   - 确保 tool call 输出能正确匹配
   - 保留 item_reference 类型的 items

5. **Header 优化**
   - 添加 conversation_id 到允许的 headers
   - 移除删除 session headers 的逻辑

## 相关 Issue
- 参考 OpenCode issue #3118 关于 item_reference 的讨论

backend/internal/handler/openai_gateway_handler.go

@@ -96,6 +96,8 @@ func (h *OpenAIGatewayHandler) Responses(c *gin.Context) {
 		return
 	}
 
+	seedOpenAISessionHeaders(c, reqBody)
+
 	userAgent := c.GetHeader("User-Agent")
 	if !openai.IsCodexCLIRequest(userAgent) {
 		existingInstructions, _ := reqBody["instructions"].(string)
@@ -299,6 +301,37 @@ func (h *OpenAIGatewayHandler) handleFailoverExhausted(c *gin.Context, statusCod
 	h.handleStreamingAwareError(c, status, errType, errMsg, streamStarted)
 }
 
+func seedOpenAISessionHeaders(c *gin.Context, reqBody map[string]any) {
+	if c.GetHeader("session_id") == "" {
+		if v := firstNonEmptyString(
+			reqBody["prompt_cache_key"],
+			reqBody["session_id"],
+			reqBody["conversation_id"],
+			reqBody["previous_response_id"],
+		); v != "" {
+			c.Request.Header.Set("session_id", v)
+		}
+	}
+	if c.GetHeader("conversation_id") == "" {
+		if v := firstNonEmptyString(reqBody["prompt_cache_key"], reqBody["conversation_id"]); v != "" {
+			c.Request.Header.Set("conversation_id", v)
+		}
+	}
+}
+
+func firstNonEmptyString(values ...any) string {
+	for _, value := range values {
+		s, ok := value.(string)
+		if ok {
+			s = strings.TrimSpace(s)
+			if s != "" {
+				return s
+			}
+		}
+	}
+	return ""
+}
+
 func (h *OpenAIGatewayHandler) mapUpstreamError(statusCode int) (int, string, string) {
 	switch statusCode {
 	case 401:

backend/internal/service/openai_codex_transform.go

@@ -317,15 +317,36 @@ func filterCodexInput(input []any) []any {
 			filtered = append(filtered, item)
 			continue
 		}
-		if typ, ok := m["type"].(string); ok && typ == "item_reference" {
+		typ, _ := m["type"].(string)
+		if typ == "item_reference" {
+			filtered = append(filtered, m)
 			continue
 		}
+		// Strip per-item ids; keep call_id only for tool call items so outputs can match.
+		if isCodexToolCallItemType(typ) {
+			callID, _ := m["call_id"].(string)
+			if strings.TrimSpace(callID) == "" {
+				if id, ok := m["id"].(string); ok && strings.TrimSpace(id) != "" {
+					m["call_id"] = id
+				}
+			}
+		}
 		delete(m, "id")
+		if !isCodexToolCallItemType(typ) {
+			delete(m, "call_id")
+		}
 		filtered = append(filtered, m)
 	}
 	return filtered
 }
 
+func isCodexToolCallItemType(typ string) bool {
+	if typ == "" {
+		return false
+	}
+	return strings.HasSuffix(typ, "_call") || strings.HasSuffix(typ, "_call_output")
+}
+
 func normalizeCodexTools(reqBody map[string]any) bool {
 	rawTools, ok := reqBody["tools"]
 	if !ok || rawTools == nil {

backend/internal/service/openai_gateway_service.go

@@ -42,6 +42,7 @@ var openaiSSEDataRe = regexp.MustCompile(`^data:\s*`)
 var openaiAllowedHeaders = map[string]bool{
 	"accept-language": true,
 	"content-type":    true,
+	"conversation_id": true,
 	"user-agent":      true,
 	"originator":      true,
 	"session_id":      true,
@@ -553,6 +554,27 @@ func (s *OpenAIGatewayService) Forward(ctx context.Context, c *gin.Context, acco
 		bodyModified = true
 	}
 
+	// Apply Codex model normalization for all OpenAI accounts
+	if model, ok := reqBody["model"].(string); ok {
+		normalizedModel := normalizeCodexModel(model)
+		if normalizedModel != "" && normalizedModel != model {
+			log.Printf("[OpenAI] Codex model normalization: %s -> %s (account: %s, type: %s, isCodexCLI: %v)",
+				model, normalizedModel, account.Name, account.Type, isCodexCLI)
+			reqBody["model"] = normalizedModel
+			mappedModel = normalizedModel
+			bodyModified = true
+		}
+	}
+
+	// Normalize reasoning.effort parameter (minimal -> none)
+	if reasoning, ok := reqBody["reasoning"].(map[string]any); ok {
+		if effort, ok := reasoning["effort"].(string); ok && effort == "minimal" {
+			reasoning["effort"] = "none"
+			bodyModified = true
+			log.Printf("[OpenAI] Normalized reasoning.effort: minimal -> none (account: %s)", account.Name)
+		}
+	}
+
 	if account.Type == AccountTypeOAuth && !isCodexCLI {
 		codexResult := applyCodexOAuthTransform(reqBody)
 		if codexResult.Modified {
@@ -783,9 +805,6 @@ func (s *OpenAIGatewayService) buildUpstreamRequest(ctx context.Context, c *gin.
 		if promptCacheKey != "" {
 			req.Header.Set("conversation_id", promptCacheKey)
 			req.Header.Set("session_id", promptCacheKey)
-		} else {
-			req.Header.Del("conversation_id")
-			req.Header.Del("session_id")
 		}
 	}