修复缺失日志标识格式

避免没有请求日志标识时输出 %!s(<nil>)，并补充日志格式化回归测试。

backend/config/config.go

@@ -153,7 +153,9 @@ func (l *logFormatter) Format(entry *log.Entry) ([]byte, error) {
 	if entry.Context != nil {
 		ctx, ok := entry.Context.(*context.Context)
 		if ok && ctx != nil {
-			b.WriteString(fmt.Sprintf("[%s]", ctx.GetValue(context.LogID)))
+			if logID := ctx.GetValue(context.LogID); logID != nil {
+				b.WriteString(fmt.Sprintf("[%v]", logID))
+			}
 		}
 	}
 	if entry.Caller != nil {

backend/config/config_security_test.go

@@ -2,12 +2,48 @@ package config
 
 import (
 	"bytes"
+	stdcontext "context"
 	"encoding/json"
 	"os"
 	"path/filepath"
 	"testing"
+
+	appcontext "git.pcux.cn/xuans/Smail/utils/context"
+	log "github.com/sirupsen/logrus"
 )
 
+func TestLogFormatterHandlesMissingLogID(t *testing.T) {
+	entry := &log.Entry{
+		Context: &appcontext.Context{Context: stdcontext.Background()},
+		Message: "配置操作",
+	}
+
+	output, err := (&logFormatter{}).Format(entry)
+	if err != nil {
+		t.Fatal(err)
+	}
+	if bytes.Contains(output, []byte("%!s(<nil>)")) {
+		t.Fatalf("log output contains a formatting error: %q", output)
+	}
+	if !bytes.Contains(output, []byte("配置操作")) {
+		t.Fatalf("log output lost the message: %q", output)
+	}
+}
+
+func TestLogFormatterIncludesLogID(t *testing.T) {
+	ctx := &appcontext.Context{Context: stdcontext.Background()}
+	ctx.SetValue(appcontext.LogID, "request-123")
+	entry := &log.Entry{Context: ctx, Message: "配置操作"}
+
+	output, err := (&logFormatter{}).Format(entry)
+	if err != nil {
+		t.Fatal(err)
+	}
+	if !bytes.Contains(output, []byte("[request-123]")) {
+		t.Fatalf("log output lost the log ID: %q", output)
+	}
+}
+
 func TestConfigCredentialsAreEncryptedAtRest(t *testing.T) {
 	oldRoot := ROOT_PATH
 	root := t.TempDir()