fix: resolve err113 lint issues with sentinel errors

cmd/chat-cli/api/client.go

@@ -4,6 +4,7 @@ package api
 import (
 	"bytes"
 	"encoding/json"
+	"errors"
 	"fmt"
 	"io"
 	"net/http"
@@ -12,6 +13,13 @@ import (
 	"time"
 )
 
+var (
+	// ErrHTTPStatus is returned when the server responds with an error status code.
+	ErrHTTPStatus = errors.New("HTTP error")
+	// ErrUnexpectedFormat is returned when the response format is unexpected.
+	ErrUnexpectedFormat = errors.New("unexpected format")
+)
+
 // Client wraps HTTP calls to the chat server API.
 type Client struct {
 	BaseURL    string
@@ -64,7 +72,7 @@ func (c *Client) do(method, path string, body any) ([]byte, error) {
 	}
 
 	if resp.StatusCode >= 400 {
-		return data, fmt.Errorf("HTTP %d: %s", resp.StatusCode, string(data))
+		return data, fmt.Errorf("%w: %d: %s", ErrHTTPStatus, resp.StatusCode, string(data))
 	}
 
 	return data, nil
@@ -150,7 +158,7 @@ func (c *Client) PollMessages(afterID string, timeout int) ([]Message, error) {
 	}
 
 	if resp.StatusCode >= 400 {
-		return nil, fmt.Errorf("HTTP %d: %s", resp.StatusCode, string(data))
+		return nil, fmt.Errorf("%w: %d: %s", ErrHTTPStatus, resp.StatusCode, string(data))
 	}
 
 	// The server may return an array directly or wrapped.
@@ -218,7 +226,7 @@ func (c *Client) GetMembers(channel string) ([]string, error) {
 			return nil, err
 		}
 		// Extract member names from whatever format.
-		return nil, fmt.Errorf("unexpected members format: %s", string(data))
+		return nil, fmt.Errorf("%w: members: %s", ErrUnexpectedFormat, string(data))
 	}
 
 	return members, nil