fix: allow empty config file bootstrap before provisioning

Treat an empty CONFIG_FILE as initial state instead of failing JSON parse, so provisioning can proceed and credentials can be saved. Ref: fosrl/pangolin#2812

websocket/config.go

@@ -71,6 +71,11 @@ func (c *Client) loadConfig() error {
 		}
 		return err
 	}
+	if len(bytes.TrimSpace(data)) == 0 {
+		logger.Info("Config file at %s is empty, will initialize it with provided values", configPath)
+		c.configNeedsSave = true
+		return nil
+	}
 
 	var config Config
 	if err := json.Unmarshal(data, &config); err != nil {

websocket/config_test.go

@@ -0,0 +1,35 @@
+package websocket
+
+import (
+	"os"
+	"path/filepath"
+	"testing"
+)
+
+func TestLoadConfig_EmptyFileMarksConfigForSave(t *testing.T) {
+	t.Setenv("CONFIG_FILE", "")
+
+	tmpDir := t.TempDir()
+	configPath := filepath.Join(tmpDir, "config.json")
+	if err := os.WriteFile(configPath, []byte(""), 0o644); err != nil {
+		t.Fatalf("failed to create empty config file: %v", err)
+	}
+
+	client := &Client{
+		config: &Config{
+			Endpoint:        "https://example.com",
+			ProvisioningKey: "spk-test",
+		},
+		clientType:     "newt",
+		configFilePath: configPath,
+	}
+
+	if err := client.loadConfig(); err != nil {
+		t.Fatalf("loadConfig returned error for empty file: %v", err)
+	}
+
+	if !client.configNeedsSave {
+		t.Fatal("expected empty config file to mark configNeedsSave")
+	}
+}
+