auto variable promotion in model piping append isn't working correctly

[mattfidler]

  mod <- function() {
    ini({
      tka <- 0.45
      label("Ka")
      tcl <- 1
      label("Cl")
      tv <- 3.45
      label("V")
      add.sd <- c(0, 0.7)
      eta.cl ~ 0.3
      eta.v ~ 0.1
    })
    model({
      ka <- exp(tka)
      cl <- exp(tcl + eta.cl)
      v <- exp(tv + eta.v)
      d/dt(depot) = -ka * depot
      d/dt(center) = ka * depot - cl/v * center
      cp = center/v
      cp ~ add(add.sd)
    })
  }

  mod5 <- mod |>
    model({
      PD <- 1-emax*cp/(ec50+cp)
      ##
      effect(0) <- e0
      kin <- e0*kout
      d/dt(effect) <- kin*PD -kout*effect
    }, append=d/dt(center))

  expect_equal(mod5$theta, c(tka = 0.45, tcl = 1, tv = 3.45, add.sd = 0.7))

  mod6 <- mod5 |>
    model({
      emax <- exp(temax)
      e0 <- exp(te0 + eta.e0)
      ec50 <- exp(tec50)
      kin <- exp(tkin)
      kout <- exp(tkout)
    }, append=NA)

  expect_equal(mod6$theta,
               c(tka = 0.45, tcl = 1, tv = 3.45, add.sd = 0.7, temax = 1, te0 = 1, tec50 = 1, tkin = 1, tkout = 1))

  expect_equal(
    mod6$omega,
    lotri({
      eta.cl ~ 0.3
      eta.v ~ 0.1
      eta.e0 ~ 1
    }))