diff --git a/internal/api/server.go b/internal/api/server.go
index a7aef0aa..7f44d085 100644
--- a/internal/api/server.go
+++ b/internal/api/server.go
@@ -59,10 +59,8 @@ type ServerOption func(*serverOptionConfig)
 
 func defaultRequestLoggerFactory(cfg *config.Config, configPath string) logging.RequestLogger {
 	configDir := filepath.Dir(configPath)
-	if base := util.WritablePath(); base != "" {
-		return logging.NewFileRequestLogger(cfg.RequestLog, filepath.Join(base, "logs"), configDir, cfg.ErrorLogsMaxFiles)
-	}
-	return logging.NewFileRequestLogger(cfg.RequestLog, "logs", configDir, cfg.ErrorLogsMaxFiles)
+	logsDir := logging.ResolveLogDirectory(cfg)
+	return logging.NewFileRequestLogger(cfg.RequestLog, logsDir, configDir, cfg.ErrorLogsMaxFiles)
 }
 
 // WithMiddleware appends additional Gin middleware during server construction.
diff --git a/internal/api/server_test.go b/internal/api/server_test.go
index 06653210..f5c18aa1 100644
--- a/internal/api/server_test.go
+++ b/internal/api/server_test.go
@@ -7,9 +7,11 @@ import (
 	"path/filepath"
 	"strings"
 	"testing"
+	"time"
 
 	gin "github.com/gin-gonic/gin"
 	proxyconfig "github.com/router-for-me/CLIProxyAPI/v6/internal/config"
+	internallogging "github.com/router-for-me/CLIProxyAPI/v6/internal/logging"
 	sdkaccess "github.com/router-for-me/CLIProxyAPI/v6/sdk/access"
 	"github.com/router-for-me/CLIProxyAPI/v6/sdk/cliproxy/auth"
 	sdkconfig "github.com/router-for-me/CLIProxyAPI/v6/sdk/config"
@@ -109,3 +111,100 @@ func TestAmpProviderModelRoutes(t *testing.T) {
 		})
 	}
 }
+
+func TestDefaultRequestLoggerFactory_UsesResolvedLogDirectory(t *testing.T) {
+	t.Setenv("WRITABLE_PATH", "")
+	t.Setenv("writable_path", "")
+
+	originalWD, errGetwd := os.Getwd()
+	if errGetwd != nil {
+		t.Fatalf("failed to get current working directory: %v", errGetwd)
+	}
+
+	tmpDir := t.TempDir()
+	if errChdir := os.Chdir(tmpDir); errChdir != nil {
+		t.Fatalf("failed to switch working directory: %v", errChdir)
+	}
+	defer func() {
+		if errChdirBack := os.Chdir(originalWD); errChdirBack != nil {
+			t.Fatalf("failed to restore working directory: %v", errChdirBack)
+		}
+	}()
+
+	// Force ResolveLogDirectory to fallback to auth-dir/logs by making ./logs not a writable directory.
+	if errWriteFile := os.WriteFile(filepath.Join(tmpDir, "logs"), []byte("not-a-directory"), 0o644); errWriteFile != nil {
+		t.Fatalf("failed to create blocking logs file: %v", errWriteFile)
+	}
+
+	configDir := filepath.Join(tmpDir, "config")
+	if errMkdirConfig := os.MkdirAll(configDir, 0o755); errMkdirConfig != nil {
+		t.Fatalf("failed to create config dir: %v", errMkdirConfig)
+	}
+	configPath := filepath.Join(configDir, "config.yaml")
+
+	authDir := filepath.Join(tmpDir, "auth")
+	if errMkdirAuth := os.MkdirAll(authDir, 0o700); errMkdirAuth != nil {
+		t.Fatalf("failed to create auth dir: %v", errMkdirAuth)
+	}
+
+	cfg := &proxyconfig.Config{
+		SDKConfig: proxyconfig.SDKConfig{
+			RequestLog: false,
+		},
+		AuthDir:           authDir,
+		ErrorLogsMaxFiles: 10,
+	}
+
+	logger := defaultRequestLoggerFactory(cfg, configPath)
+	fileLogger, ok := logger.(*internallogging.FileRequestLogger)
+	if !ok {
+		t.Fatalf("expected *FileRequestLogger, got %T", logger)
+	}
+
+	errLog := fileLogger.LogRequestWithOptions(
+		"/v1/chat/completions",
+		http.MethodPost,
+		map[string][]string{"Content-Type": []string{"application/json"}},
+		[]byte(`{"input":"hello"}`),
+		http.StatusBadGateway,
+		map[string][]string{"Content-Type": []string{"application/json"}},
+		[]byte(`{"error":"upstream failure"}`),
+		nil,
+		nil,
+		nil,
+		true,
+		"issue-1711",
+		time.Now(),
+		time.Now(),
+	)
+	if errLog != nil {
+		t.Fatalf("failed to write forced error request log: %v", errLog)
+	}
+
+	authLogsDir := filepath.Join(authDir, "logs")
+	authEntries, errReadAuthDir := os.ReadDir(authLogsDir)
+	if errReadAuthDir != nil {
+		t.Fatalf("failed to read auth logs dir %s: %v", authLogsDir, errReadAuthDir)
+	}
+	foundErrorLogInAuthDir := false
+	for _, entry := range authEntries {
+		if strings.HasPrefix(entry.Name(), "error-") && strings.HasSuffix(entry.Name(), ".log") {
+			foundErrorLogInAuthDir = true
+			break
+		}
+	}
+	if !foundErrorLogInAuthDir {
+		t.Fatalf("expected forced error log in auth fallback dir %s, got entries: %+v", authLogsDir, authEntries)
+	}
+
+	configLogsDir := filepath.Join(configDir, "logs")
+	configEntries, errReadConfigDir := os.ReadDir(configLogsDir)
+	if errReadConfigDir != nil && !os.IsNotExist(errReadConfigDir) {
+		t.Fatalf("failed to inspect config logs dir %s: %v", configLogsDir, errReadConfigDir)
+	}
+	for _, entry := range configEntries {
+		if strings.HasPrefix(entry.Name(), "error-") && strings.HasSuffix(entry.Name(), ".log") {
+			t.Fatalf("unexpected forced error log in config dir %s", configLogsDir)
+		}
+	}
+}