fix(sync): add ClientSequence and LastSeenServerSeq to Op struct and Push

- Add ClientSequence and LastSeenServerSeq fields to sync.Op struct
- Fix Client.Push() to copy these fields to PushOp
- Add GetDeviceID() method to sync.Service

.gitignore

@@ -25,6 +25,7 @@ frontend/bindings/
 /verstak-gui
 /verstak-cli
 /verstak-server
+/verstak
 
 # Vault data
 .verstak/

internal/core/sync/client.go

@@ -130,6 +130,19 @@ func (c *Client) Login(username, password string) (token string, err error) {
 	return resp.Token, nil
 }
 
+// TestAuth checks credentials without creating a device.
+func (c *Client) TestAuth(serverURL, username, password string) error {
+	body := map[string]string{"username": username, "password": password}
+	savedURL := c.ServerURL
+	savedKey := c.APIKey
+	c.ServerURL = serverURL
+	c.APIKey = ""
+	err := c.post("/api/auth/test", body, nil)
+	c.ServerURL = savedURL
+	c.APIKey = savedKey
+	return err
+}
+
 // PushRequest is the payload for POST /sync/push.
 type PushRequest struct {
 	DeviceID      string   `json:"device_id"`
@@ -161,12 +174,14 @@ func (c *Client) Push(ops []Op) (*PushResponse, error) {
 	pushOps := make([]PushOp, len(ops))
 	for i, op := range ops {
 		pushOps[i] = PushOp{
-			OpID:        op.OpID,
-			EntityType:  op.EntityType,
-			EntityID:    op.EntityID,
-			OpType:      op.OpType,
-			PayloadJSON: op.PayloadJSON,
-			CreatedAt:   op.CreatedAt,
+			OpID:              op.OpID,
+			EntityType:        op.EntityType,
+			EntityID:          op.EntityID,
+			OpType:            op.OpType,
+			PayloadJSON:       op.PayloadJSON,
+			ClientSequence:    op.ClientSequence,
+			LastSeenServerSeq: op.LastSeenServerSeq,
+			CreatedAt:         op.CreatedAt,
 		}
 	}
 	req := PushRequest{DeviceID: c.DeviceID, Ops: pushOps}

internal/core/sync/sync.go

@@ -30,16 +30,18 @@ const (
 
 // Op represents a sync operation.
 type Op struct {
-	ID             string `json:"id"`
-	OpID           string `json:"op_id"`
-	ServerSequence int    `json:"server_sequence,omitempty"`
-	DeviceID       string `json:"device_id,omitempty"`
-	EntityType     string `json:"entity_type"`
-	EntityID       string `json:"entity_id"`
-	OpType         string `json:"op_type"`
-	PayloadJSON    string `json:"payload_json"`
-	CreatedAt      string `json:"created_at"`
-	PushedAt       *string `json:"pushed_at,omitempty"`
+	ID                string   `json:"id"`
+	OpID              string   `json:"op_id"`
+	ServerSequence    int      `json:"server_sequence,omitempty"`
+	DeviceID          string   `json:"device_id,omitempty"`
+	EntityType        string   `json:"entity_type"`
+	EntityID          string   `json:"entity_id"`
+	OpType            string   `json:"op_type"`
+	PayloadJSON       string   `json:"payload_json"`
+	CreatedAt         string   `json:"created_at"`
+	PushedAt          *string  `json:"pushed_at,omitempty"`
+	ClientSequence    int      `json:"client_sequence,omitempty"`
+	LastSeenServerSeq int      `json:"last_seen_server_seq,omitempty"`
 }
 
 // Service records and manages sync operations.