fix: fail fast in register and honor GITEA_MAX_REG_ATTEMPTS (#1197)

`gitea-runner register` pinged the instance in an unbounded loop, so a permanent failure like an untrusted certificate or a wrong URL never returned. It now pings once and returns the error, like other one-shot commands.

The image entrypoint keeps retrying registration indefinitely by default, like the daemon, so a container without a restart policy still recovers once Gitea is reachable. `GITEA_MAX_REG_ATTEMPTS` had no effect because its counter was incremented outside the loop. When set, it now caps the attempts, after which the entrypoint exits non-zero.

Fixes: https://gitea.com/gitea/runner/issues/1195
Co-authored-by: silverwind <[email protected]>
Reviewed-on: https://gitea.com/gitea/runner/pulls/1197
Reviewed-by: Lunny Xiao <[email protected]>
Reviewed-by: silverwind <[email protected]>
Co-authored-by: bircni <[email protected]>

internal/app/cmd/register_test.go

@@ -4,7 +4,11 @@
 package cmd
 
 import (
+	"net/http"
+	"net/http/httptest"
 	"os"
+	"path/filepath"
+	"sync/atomic"
 	"testing"
 
 	"gitea.com/gitea/runner/internal/pkg/config"
@@ -246,3 +250,18 @@ func TestInitInputs(t *testing.T) {
 		require.Nil(t, inputs.Labels)
 	})
 }
+
+func TestDoRegisterReturnsPingErrorWithoutRetrying(t *testing.T) {
+	var requests atomic.Int32
+	server := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, _ *http.Request) {
+		requests.Add(1)
+		w.WriteHeader(http.StatusServiceUnavailable)
+	}))
+	defer server.Close()
+
+	cfg := &config.Config{}
+	cfg.Runner.File = filepath.Join(t.TempDir(), ".runner")
+	err := doRegister(t.Context(), cfg, &registerInputs{InstanceAddr: server.URL, RunnerName: "runner"})
+	assert.ErrorContains(t, err, "cannot ping the Gitea instance server")
+	assert.Equal(t, int32(1), requests.Load())
+}