refactor(copilot): address PR review feedback

- Simplify error type checking in oauth.go using errors.As directly
- Remove redundant errors.As call in GetUserFriendlyMessage
- Remove unused CachedAPIToken and TokenManager types (dead code)

internal/auth/copilot/copilot_auth.go

@@ -208,77 +208,6 @@ func (c *CopilotAuth) MakeAuthenticatedRequest(ctx context.Context, method, url
 	return req, nil
 }
 
-// CachedAPIToken manages caching of Copilot API tokens.
-type CachedAPIToken struct {
-	Token     *CopilotAPIToken
-	ExpiresAt time.Time
-}
-
-// IsExpired checks if the cached token has expired.
-func (c *CachedAPIToken) IsExpired() bool {
-	if c.Token == nil {
-		return true
-	}
-	// Add a 5-minute buffer before expiration
-	return time.Now().Add(5 * time.Minute).After(c.ExpiresAt)
-}
-
-// TokenManager handles caching and refreshing of Copilot API tokens.
-type TokenManager struct {
-	auth        *CopilotAuth
-	githubToken string
-	cachedToken *CachedAPIToken
-}
-
-// NewTokenManager creates a new token manager for handling Copilot API tokens.
-func NewTokenManager(auth *CopilotAuth, githubToken string) *TokenManager {
-	return &TokenManager{
-		auth:        auth,
-		githubToken: githubToken,
-	}
-}
-
-// GetToken returns a valid Copilot API token, refreshing if necessary.
-func (tm *TokenManager) GetToken(ctx context.Context) (*CopilotAPIToken, error) {
-	if tm.cachedToken != nil && !tm.cachedToken.IsExpired() {
-		return tm.cachedToken.Token, nil
-	}
-
-	// Fetch a new API token
-	apiToken, err := tm.auth.GetCopilotAPIToken(ctx, tm.githubToken)
-	if err != nil {
-		return nil, err
-	}
-
-	// Cache the token
-	expiresAt := time.Now().Add(30 * time.Minute) // Default 30 min cache
-	if apiToken.ExpiresAt > 0 {
-		expiresAt = time.Unix(apiToken.ExpiresAt, 0)
-	}
-
-	tm.cachedToken = &CachedAPIToken{
-		Token:     apiToken,
-		ExpiresAt: expiresAt,
-	}
-
-	return apiToken, nil
-}
-
-// GetAuthorizationHeader returns the authorization header value for API requests.
-func (tm *TokenManager) GetAuthorizationHeader(ctx context.Context) (string, error) {
-	token, err := tm.GetToken(ctx)
-	if err != nil {
-		return "", err
-	}
-	return "Bearer " + token.Token, nil
-}
-
-// UpdateGitHubToken updates the GitHub access token used for getting API tokens.
-func (tm *TokenManager) UpdateGitHubToken(githubToken string) {
-	tm.githubToken = githubToken
-	tm.cachedToken = nil // Invalidate cache
-}
-
 // BuildChatCompletionURL builds the URL for chat completions API.
 func BuildChatCompletionURL() string {
 	return copilotAPIEndpoint + "/chat/completions"

internal/auth/copilot/errors.go

@@ -140,10 +140,8 @@ func IsOAuthError(err error) bool {
 
 // GetUserFriendlyMessage returns a user-friendly error message based on the error type.
 func GetUserFriendlyMessage(err error) string {
-	switch {
-	case IsAuthenticationError(err):
-		var authErr *AuthenticationError
-		errors.As(err, &authErr)
+	var authErr *AuthenticationError
+	if errors.As(err, &authErr) {
 		switch authErr.Type {
 		case "device_code_failed":
 			return "Failed to start GitHub authentication. Please check your network connection and try again."
@@ -164,9 +162,10 @@ func GetUserFriendlyMessage(err error) string {
 		default:
 			return "Authentication failed. Please try again."
 		}
-	case IsOAuthError(err):
-		var oauthErr *OAuthError
-		errors.As(err, &oauthErr)
+	}
+
+	var oauthErr *OAuthError
+	if errors.As(err, &oauthErr) {
 		switch oauthErr.Code {
 		case "access_denied":
 			return "Authentication was cancelled or denied."
@@ -177,7 +176,7 @@ func GetUserFriendlyMessage(err error) string {
 		default:
 			return fmt.Sprintf("Authentication failed: %s", oauthErr.Description)
 		}
-	default:
-		return "An unexpected error occurred. Please try again."
 	}
+
+	return "An unexpected error occurred. Please try again."
 }

internal/auth/copilot/oauth.go

@@ -3,6 +3,7 @@ package copilot
 import (
 	"context"
 	"encoding/json"
+	"errors"
 	"fmt"
 	"io"
 	"net/http"
@@ -118,12 +119,7 @@ func (c *DeviceFlowClient) PollForToken(ctx context.Context, deviceCode *DeviceC
 			token, err := c.exchangeDeviceCode(ctx, deviceCode.DeviceCode)
 			if err != nil {
 				var authErr *AuthenticationError
-				if IsAuthenticationError(err) {
-					if ok := (err.(*AuthenticationError)); ok != nil {
-						authErr = ok
-					}
-				}
-				if authErr != nil {
+				if errors.As(err, &authErr) {
 					switch authErr.Type {
 					case ErrAuthorizationPending.Type:
 						// Continue polling