fix: address review findings from reviews #2955 and #2958

- Convert handleResponse to package-level function (unused receiver) [#17955]
- Add clarifying comment for nil resp on transport error [#17956]
- Use consistent %w wrapping in dual-unmarshal error path [#17957]
- Add SafeError() method to APIError for safe logging [#17964]
- Enforce safe CheckRedirect policy in SetHTTPClient [#17965]
- Add tests for SafeError and SetHTTPClient enforcement

github/client.go

@@ -47,6 +47,13 @@ func (e *APIError) Error() string {
 	return fmt.Sprintf("HTTP %d: %s", e.StatusCode, body)
 }
 
+// SafeError returns the error string without response body content,
+// suitable for logging in contexts where upstream response data should
+// not be exposed.
+func (e *APIError) SafeError() string {
+	return fmt.Sprintf("HTTP %d", e.StatusCode)
+}
+
 // IsNotFound reports whether an error is an API 404 response.
 func IsNotFound(err error) bool {
 	if apiErr, ok := asAPIError(err); ok {
@@ -172,6 +179,12 @@ func (c *Client) SetHTTPClient(hc *http.Client) {
 			Timeout:       30 * time.Second,
 			CheckRedirect: defaultCheckRedirect,
 		}
+	} else if hc.CheckRedirect == nil {
+		// Enforce safe redirect policy when caller provides a client without one.
+		// The default net/http behavior follows up to 10 redirects and forwards
+		// all headers (including Authorization) to any host, which can leak
+		// credentials on cross-host redirects.
+		hc.CheckRedirect = defaultCheckRedirect
 	}
 	c.httpClient = hc
 }
@@ -252,10 +265,11 @@ func (c *Client) doRequest(ctx context.Context, method, reqURL string, accept st
 
 		resp, err := c.httpClient.Do(req)
 		if err != nil {
+			// Transport errors (DNS, TLS, timeout) yield nil resp; no body to close.
 			return nil, fmt.Errorf("do request: %w", err)
 		}
 
-		body, done, err := c.handleResponse(resp, maxResponseBytes, maxErrorBodyBytes)
+		body, done, err := handleResponse(resp, maxResponseBytes, maxErrorBodyBytes)
 		if done {
 			return body, err
 		}
@@ -300,7 +314,7 @@ func (c *Client) doRequest(ctx context.Context, method, reqURL string, accept st
 // handleResponse reads and closes the response body, returning the result.
 // It uses defer to ensure the body is always closed regardless of code path.
 // Returns (body, done, err) where done=true means the caller should return immediately.
-func (c *Client) handleResponse(resp *http.Response, maxRespBytes int, maxErrBytes int) ([]byte, bool, error) {
+func handleResponse(resp *http.Response, maxRespBytes int, maxErrBytes int) ([]byte, bool, error) {
 	defer resp.Body.Close()
 
 	if resp.StatusCode >= 200 && resp.StatusCode < 300 {