fix(coverage): production show-page crash and stale device on PubSub refresh

- show.html.heex: `@coverage.device_id and ...` raised BadBooleanError
  in production because device_id is a UUID string, not a boolean. Use
  is_nil/1 checks instead.
- show.ex: handle_info/2 was reloading the coverage without preloading
  :device, so the device row vanished from the UI on every status
  broadcast. Preload :device alongside the reload.
- coverage_worker: thread the precomputed tx_height through the pixel
  loop instead of re-deriving `coverage.height_agl_m + ...` per pixel
  with inconsistent nil-safety vs. compute_pixels/6.

lib/towerops/workers/coverage_worker.ex

@@ -140,18 +140,11 @@ defmodule Towerops.Workers.CoverageWorker do
         fn r ->
           row_lat = max_lat - (r + 0.5) * cell_lat
 
+          tx = {{lat, lon}, tx_z, tx_height}
+
           for c <- 0..(ncols - 1) do
             pixel_lon = min_lon + (c + 0.5) * cell_lon
-
-            compute_pixel(
-              coverage,
-              antenna,
-              {lat, lon},
-              tx_z,
-              {row_lat, pixel_lon},
-              grid,
-              eirp
-            )
+            compute_pixel(coverage, antenna, tx, {row_lat, pixel_lon}, grid, eirp)
           end
         end,
         ordered: true,
@@ -173,7 +166,7 @@ defmodule Towerops.Workers.CoverageWorker do
      }}
   end
 
-  defp compute_pixel(coverage, antenna, tx_latlon, tx_z, rx_latlon, grid, eirp) do
+  defp compute_pixel(coverage, antenna, {tx_latlon, _tx_z, _tx_height} = tx, rx_latlon, grid, eirp) do
     distance_m = Profile.great_circle_distance_m(tx_latlon, rx_latlon)
 
     cond do
@@ -184,15 +177,14 @@ defmodule Towerops.Workers.CoverageWorker do
         :nan
 
       true ->
-        do_compute_pixel(coverage, antenna, tx_latlon, tx_z, rx_latlon, grid, eirp, distance_m)
+        do_compute_pixel(coverage, antenna, tx, rx_latlon, grid, eirp, distance_m)
     end
   end
 
   defp do_compute_pixel(
          coverage,
          antenna,
-         {tx_lat, tx_lon} = tx_latlon,
-         tx_z,
+         {{tx_lat, tx_lon} = tx_latlon, tx_z, tx_height},
          {rx_lat, rx_lon} = rx_latlon,
          grid,
          eirp,
@@ -202,10 +194,10 @@ defmodule Towerops.Workers.CoverageWorker do
     samples = max(3, min(@profile_samples, ceil(distance_m / coverage.cell_size_m) + 2))
     profile = Profile.sample(grid, tx_latlon, rx_latlon, samples)
 
-    # Replace TX endpoint with the absolute Z (so diffraction sees the correct
-    # antenna height). The receiver height is added inside Propagation.
+    # Replace TX endpoint with the ground elevation under the antenna (so the
+    # path loss model sees the correct antenna height above terrain).
     [_old_first | rest] = profile
-    profile = [tx_z - (coverage.height_agl_m + (coverage.height_above_rooftop_m || 0.0)) | rest]
+    profile = [tx_z - tx_height | rest]
 
     # 2. Antenna pattern attenuation at this bearing/elevation.
     bearing_offset = bearing_offset_deg(tx_lat, tx_lon, rx_lat, rx_lon, coverage.azimuth_deg)
@@ -218,7 +210,7 @@ defmodule Towerops.Workers.CoverageWorker do
         distance_m,
         coverage.frequency_mhz * 1.0,
         profile,
-        coverage.height_agl_m + (coverage.height_above_rooftop_m || 0.0),
+        tx_height,
         coverage.receiver_height_m || 3.0
       )
 

lib/towerops_web/live/coverage_live/show.ex

@@ -61,7 +61,9 @@ defmodule ToweropsWeb.CoverageLive.Show do
   @impl true
   def handle_info({:coverage_status, _status, _extra}, socket) do
     coverage =
-      Coverages.get_coverage!(socket.assigns.organization.id, socket.assigns.coverage.id)
+      socket.assigns.organization.id
+      |> Coverages.get_coverage!(socket.assigns.coverage.id)
+      |> Towerops.Repo.preload(:device)
 
     eirp =
       Coverage.eirp_dbm(

lib/towerops_web/live/coverage_live/show.html.heex

@@ -199,7 +199,8 @@
           />
           <.param_row
             :if={
-              @coverage.device_id and Ecto.assoc_loaded?(@coverage.device) and @coverage.device
+              not is_nil(@coverage.device_id) and Ecto.assoc_loaded?(@coverage.device) and
+                not is_nil(@coverage.device)
             }
             label={t("Device")}
             value={@coverage.device.name || @coverage.device.ip_address}