feat: persist diagnostic logs with daily rotation and retention

internal/logger/logger.go

@@ -11,7 +11,7 @@ type Logger struct {
 	*zap.Logger
 }
 
-func New(level, output string) *Logger {
+func New(level, output string, diagnostics ...DiagnosticOptions) *Logger {
 	var zapLevel zapcore.Level
 	switch level {
 	case "debug":
@@ -34,6 +34,8 @@ func New(level, output string) *Logger {
 	var writeSyncer zapcore.WriteSyncer
 	if output == "stdout" {
 		writeSyncer = zapcore.AddSync(os.Stdout)
+	} else if output == "stderr" {
+		writeSyncer = zapcore.AddSync(os.Stderr)
 	} else {
 		file, err := os.OpenFile(output, os.O_CREATE|os.O_WRONLY|os.O_APPEND, 0666)
 		if err != nil {
@@ -49,6 +51,18 @@ func New(level, output string) *Logger {
 		zapLevel,
 	)
 
+	options := DiagnosticOptions{}
+	if len(diagnostics) > 0 {
+		options = diagnostics[0]
+	}
+	if !options.Disabled {
+		// The diagnostic threshold is independent of the primary output level.
+		core = zapcore.NewTee(core, zapcore.NewCore(
+			zapcore.NewJSONEncoder(config.EncoderConfig),
+			newDailyWriter(options), zapcore.WarnLevel,
+		))
+	}
+
 	logger := zap.New(core, zap.AddCaller(), zap.AddStacktrace(zapcore.ErrorLevel))
 
 	return &Logger{Logger: logger}