@yegor256, regarding introducing a new variable. Do you like introduce a new field requestURI and use it as below

    RtRelease(final Request req, final Coordinates coords, final int nmbr) {
        this.release = nmbr;
        this.request = req.uri()
            .path("/repos")
            .path(coords.user())
            .path(coords.repo())
            .path("/releases")
            .path(String.valueOf(this.release))
            .back();
        this.requestURI = this.request.uri();
    }

  @Override
    public Request iterate(final Request req,  final Coordinates coords) {
        return this.requestURI
            .path("/assets")
            .back();
    }