fix: use Responses-compatible function tool_choice format

backend/internal/service/openai_codex_transform.go

@@ -141,9 +141,7 @@ func applyCodexOAuthTransform(reqBody map[string]any, isCodexCLI bool, isCompact
 			if name, ok := fcObj["name"].(string); ok && strings.TrimSpace(name) != "" {
 				reqBody["tool_choice"] = map[string]any{
 					"type": "function",
-					"function": map[string]any{
-						"name": name,
-					},
+					"name": name,
 				}
 			}
 		}
@@ -219,9 +217,38 @@ func normalizeCodexToolChoice(reqBody map[string]any) bool {
 		return false
 	}
 	choiceType := strings.TrimSpace(firstNonEmptyString(choiceMap["type"]))
-	if choiceType == "" || codexToolsContainType(reqBody["tools"], choiceType) {
+	if choiceType == "" {
 		return false
 	}
+	modified := false
+	if choiceType == "function" {
+		name := strings.TrimSpace(firstNonEmptyString(choiceMap["name"]))
+		if name == "" {
+			if function, ok := choiceMap["function"].(map[string]any); ok {
+				name = strings.TrimSpace(firstNonEmptyString(function["name"]))
+			}
+		}
+		if name == "" {
+			reqBody["tool_choice"] = "auto"
+			return true
+		}
+		if strings.TrimSpace(firstNonEmptyString(choiceMap["name"])) != name {
+			choiceMap["name"] = name
+			modified = true
+		}
+		if _, ok := choiceMap["function"]; ok {
+			delete(choiceMap, "function")
+			modified = true
+		}
+		if !codexToolsContainFunctionName(reqBody["tools"], name) {
+			reqBody["tool_choice"] = "auto"
+			return true
+		}
+		return modified
+	}
+	if codexToolsContainType(reqBody["tools"], choiceType) {
+		return modified
+	}
 	reqBody["tool_choice"] = "auto"
 	return true
 }
@@ -243,6 +270,33 @@ func codexToolsContainType(rawTools any, toolType string) bool {
 	return false
 }
 
+func codexToolsContainFunctionName(rawTools any, name string) bool {
+	tools, ok := rawTools.([]any)
+	if !ok || strings.TrimSpace(name) == "" {
+		return false
+	}
+	normalizedName := strings.TrimSpace(name)
+	for _, rawTool := range tools {
+		tool, ok := rawTool.(map[string]any)
+		if !ok {
+			continue
+		}
+		if strings.TrimSpace(firstNonEmptyString(tool["type"])) != "function" {
+			continue
+		}
+		toolName := strings.TrimSpace(firstNonEmptyString(tool["name"]))
+		if toolName == "" {
+			if function, ok := tool["function"].(map[string]any); ok {
+				toolName = strings.TrimSpace(firstNonEmptyString(function["name"]))
+			}
+		}
+		if toolName == normalizedName {
+			return true
+		}
+	}
+	return false
+}
+
 func normalizeCodexToolRoleMessages(input []any) ([]any, bool) {
 	if len(input) == 0 {
 		return input, false