chore(logging): 完成后端日志审计与结构化迁移

- 将高密度服务与处理器日志迁移到新日志系统（LegacyPrintf/结构化日志）
- 增加 stdlog bridge 与兼容测试，保留旧日志捕获能力
- 将 OpenAI 断流告警改为结构化 Warn 并改造对应测试为 sink 捕获
- 补齐后端相关文件 logger 引用并通过全量 go test

backend/internal/pkg/logger/stdlog_bridge_test.go

@@ -0,0 +1,165 @@
+package logger
+
+import (
+	"io"
+	"log"
+	"os"
+	"strings"
+	"testing"
+)
+
+func TestInferStdLogLevel(t *testing.T) {
+	cases := []struct {
+		msg  string
+		want Level
+	}{
+		{msg: "Warning: queue full", want: LevelWarn},
+		{msg: "Forward request failed: timeout", want: LevelError},
+		{msg: "[ERROR] upstream unavailable", want: LevelError},
+		{msg: "service started", want: LevelInfo},
+		{msg: "debug: cache miss", want: LevelDebug},
+	}
+
+	for _, tc := range cases {
+		got := inferStdLogLevel(tc.msg)
+		if got != tc.want {
+			t.Fatalf("inferStdLogLevel(%q)=%v want=%v", tc.msg, got, tc.want)
+		}
+	}
+}
+
+func TestNormalizeStdLogMessage(t *testing.T) {
+	raw := "  [TokenRefresh]  cycle complete \n total=1   failed=0 \n"
+	got := normalizeStdLogMessage(raw)
+	want := "[TokenRefresh] cycle complete total=1 failed=0"
+	if got != want {
+		t.Fatalf("normalizeStdLogMessage()=%q want=%q", got, want)
+	}
+}
+
+func TestStdLogBridgeRoutesLevels(t *testing.T) {
+	origStdout := os.Stdout
+	origStderr := os.Stderr
+	stdoutR, stdoutW, err := os.Pipe()
+	if err != nil {
+		t.Fatalf("create stdout pipe: %v", err)
+	}
+	stderrR, stderrW, err := os.Pipe()
+	if err != nil {
+		t.Fatalf("create stderr pipe: %v", err)
+	}
+	os.Stdout = stdoutW
+	os.Stderr = stderrW
+	t.Cleanup(func() {
+		os.Stdout = origStdout
+		os.Stderr = origStderr
+		_ = stdoutR.Close()
+		_ = stdoutW.Close()
+		_ = stderrR.Close()
+		_ = stderrW.Close()
+	})
+
+	if err := Init(InitOptions{
+		Level:       "debug",
+		Format:      "json",
+		ServiceName: "sub2api",
+		Environment: "test",
+		Output: OutputOptions{
+			ToStdout: true,
+			ToFile:   false,
+		},
+		Sampling: SamplingOptions{Enabled: false},
+	}); err != nil {
+		t.Fatalf("Init() error: %v", err)
+	}
+
+	log.Printf("service started")
+	log.Printf("Warning: queue full")
+	log.Printf("Forward request failed: timeout")
+	Sync()
+
+	_ = stdoutW.Close()
+	_ = stderrW.Close()
+	stdoutBytes, _ := io.ReadAll(stdoutR)
+	stderrBytes, _ := io.ReadAll(stderrR)
+	stdoutText := string(stdoutBytes)
+	stderrText := string(stderrBytes)
+
+	if !strings.Contains(stdoutText, "service started") {
+		t.Fatalf("stdout missing info log: %s", stdoutText)
+	}
+	if !strings.Contains(stderrText, "Warning: queue full") {
+		t.Fatalf("stderr missing warn log: %s", stderrText)
+	}
+	if !strings.Contains(stderrText, "Forward request failed: timeout") {
+		t.Fatalf("stderr missing error log: %s", stderrText)
+	}
+	if !strings.Contains(stderrText, "\"legacy_stdlog\":true") {
+		t.Fatalf("stderr missing legacy_stdlog marker: %s", stderrText)
+	}
+}
+
+func TestLegacyPrintfRoutesLevels(t *testing.T) {
+	origStdout := os.Stdout
+	origStderr := os.Stderr
+	stdoutR, stdoutW, err := os.Pipe()
+	if err != nil {
+		t.Fatalf("create stdout pipe: %v", err)
+	}
+	stderrR, stderrW, err := os.Pipe()
+	if err != nil {
+		t.Fatalf("create stderr pipe: %v", err)
+	}
+	os.Stdout = stdoutW
+	os.Stderr = stderrW
+	t.Cleanup(func() {
+		os.Stdout = origStdout
+		os.Stderr = origStderr
+		_ = stdoutR.Close()
+		_ = stdoutW.Close()
+		_ = stderrR.Close()
+		_ = stderrW.Close()
+	})
+
+	if err := Init(InitOptions{
+		Level:       "debug",
+		Format:      "json",
+		ServiceName: "sub2api",
+		Environment: "test",
+		Output: OutputOptions{
+			ToStdout: true,
+			ToFile:   false,
+		},
+		Sampling: SamplingOptions{Enabled: false},
+	}); err != nil {
+		t.Fatalf("Init() error: %v", err)
+	}
+
+	LegacyPrintf("service.test", "request started")
+	LegacyPrintf("service.test", "Warning: queue full")
+	LegacyPrintf("service.test", "forward failed: timeout")
+	Sync()
+
+	_ = stdoutW.Close()
+	_ = stderrW.Close()
+	stdoutBytes, _ := io.ReadAll(stdoutR)
+	stderrBytes, _ := io.ReadAll(stderrR)
+	stdoutText := string(stdoutBytes)
+	stderrText := string(stderrBytes)
+
+	if !strings.Contains(stdoutText, "request started") {
+		t.Fatalf("stdout missing info log: %s", stdoutText)
+	}
+	if !strings.Contains(stderrText, "Warning: queue full") {
+		t.Fatalf("stderr missing warn log: %s", stderrText)
+	}
+	if !strings.Contains(stderrText, "forward failed: timeout") {
+		t.Fatalf("stderr missing error log: %s", stderrText)
+	}
+	if !strings.Contains(stderrText, "\"legacy_printf\":true") {
+		t.Fatalf("stderr missing legacy_printf marker: %s", stderrText)
+	}
+	if !strings.Contains(stderrText, "\"component\":\"service.test\"") {
+		t.Fatalf("stderr missing component field: %s", stderrText)
+	}
+}