agent: command.update handler + updater package (Linux + Windows)

cmd/agent/main.go

@@ -148,6 +148,7 @@ func run() error {
 		resticBin:                 resticBin,
 		resticVer:                 snap.ResticVersion,
 		resticSupportsNoOwnership: resticSupportsNoOwnership,
+		serverURL:                 cfg.ServerURL,
 		secrets:                   sec,
 		scheduler:                 scheduler.New(),
 	}
@@ -214,6 +215,7 @@ type dispatcher struct {
 	resticBin                 string
 	resticVer                 string // e.g. "0.17.1"; empty if restic isn't installed yet
 	resticSupportsNoOwnership bool   // captured at startup from `restic restore --help`
+	serverURL                 string // base URL of the server (used by the self-update fetch)
 	secrets                   *secrets.Store
 	scheduler                 *scheduler.Scheduler
 
@@ -395,10 +397,12 @@ func (d *dispatcher) handle(ctx context.Context, env api.Envelope, tx wsclient.S
 				"up_kbps", up, "down_kbps", down)
 		}
 
-	case api.MsgAgentUpdateAvail:
-		var p api.AgentUpdateAvailablePayload
-		_ = env.UnmarshalPayload(&p)
-		slog.Info("ws agent: update available", "version", p.LatestVersion, "url", p.PackageURL)
+	case api.MsgCommandUpdate:
+		var p api.CommandUpdatePayload
+		if err := env.UnmarshalPayload(&p); err != nil {
+			return fmt.Errorf("command.update: %w", err)
+		}
+		go d.runUpdate(ctx, p, tx)
 
 	default:
 		slog.Debug("ws agent: ignored message", "type", env.Type)