fix: clear consumed ephemeral registration state (#1256)

Ephemeral registrations are single-use, but the daemon kept `.runner` after the task, so a restarted container failed `Declare` with `unregistered runner` forever.

An ephemeral runner now removes its registration file as soon as it fetches a task, so a container killed mid-job registers afresh on restart. It also removes the file when Gitea answers `unregistered runner` at startup or while polling. A proxy's 401 does not count. Persistent runners keep their file, because Gitea sends the same reply for a token mismatch.

Closes https://gitea.com/gitea/runner/issues/818

---------

Co-authored-by: silverwind <[email protected]>
Reviewed-on: https://gitea.com/gitea/runner/pulls/1256
Reviewed-by: silverwind <[email protected]>

internal/pkg/client/client.go

@@ -5,6 +5,7 @@ package client
 
 import (
 	"context"
+	"errors"
 
 	"connectrpc.com/connect"
 	"gitea.dev/actionslib/runner/v1"
@@ -18,3 +19,10 @@ type Client interface {
 	UpdateLog(context.Context, *connect.Request[runnerv1.UpdateLogRequest]) (*connect.Response[runnerv1.UpdateLogResponse], error)
 	UpdateTask(context.Context, *connect.Request[runnerv1.UpdateTaskRequest]) (*connect.Response[runnerv1.UpdateTaskResponse], error)
 }
+
+// IsRegistrationRejected reports whether Gitea itself answered "unregistered runner", unlike a proxy's bare 401.
+func IsRegistrationRejected(err error) bool {
+	var connectErr *connect.Error
+	return errors.As(err, &connectErr) && connectErr.Code() == connect.CodeUnknown && connect.IsWireError(err) &&
+		connectErr.Message() == "rpc error: code = Unauthenticated desc = unregistered runner"
+}