Log original error before wrapping as APIError

When DoWithRetry fails, log the underlying error at ERROR level before
replacing it with the generic "Internal API unreachable" APIError. This
preserves the sanitised user-facing message while keeping the root cause
visible in logs for debugging.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

Author: e_forbes

internal/clients/gitlab/client.go

@@ -11,12 +11,14 @@ import (
 	"errors"
 	"fmt"
 	"io"
+	"log/slog"
 	"net/http"
 	"path"
 	"strings"
 	"time"
 
 	"gitlab.com/gitlab-org/labkit/correlation"
+	lablog "gitlab.com/gitlab-org/labkit/v2/log"
 	"gitlab.com/gitlab-org/labkit/v2/httpclient"
 
 	"gitlab.com/gitlab-org/gitlab-shell/v14/client"
@@ -161,6 +163,7 @@ func (c *Client) do(ctx context.Context, method, apiPath string, data any) (*htt
 
 	resp, err := c.inner.DoWithRetry(req, nil)
 	if err != nil {
+		slog.ErrorContext(ctx, "Internal API unreachable", lablog.ErrorMessage(err.Error()))
 		return nil, &client.APIError{Msg: "Internal API unreachable"}
 	}
 	return resp, nil