feat(path): show buildings stacked on terrain in path elevation profile

Path calculator now queries Microsoft Building Footprints for the
tallest structure within 80m of each profile sample and renders a red
"Buildings" dataset on top of the terrain layer in the elevation chart.

Also normalize on-disk grid HRRR cells to include the legacy
:min_refractivity_gradient / :surface_refractivity / :ducting_detected
keys (mapped from :native_min_gradient and :duct_count). Path-calculator
crashed in prod with KeyError when a path's HRRR points came from the
new on-disk grid format instead of the DB profile shape.

assets/js/elevation_profile_hook.ts

@@ -8,6 +8,7 @@ interface ProfilePoint {
   elev: number
   beam: number
   r1: number
+  building_m?: number
 }
 
 interface DuctRaw {
@@ -191,6 +192,15 @@ export const ElevationProfile: ElevationProfileHook = {
       return (p.elev + bulge) * M2FT
     })
 
+    // Buildings: terrain + max nearby building height. Same earth bulge so the
+    // dataset stacks correctly on top of terrain.
+    const hasBuildings = points.some(p => (p.building_m || 0) > 0.5)
+    const buildingTops = points.map((p, i) => {
+      const f = n > 0 ? i / n : 0
+      const bulge = (f * dTotal * (1 - f) * dTotal) / (2 * k * R)
+      return (p.elev + (p.building_m || 0) + bulge) * M2FT
+    })
+
     // LOS beam: straight line from antenna A to antenna B
     const losLine = points.map(p => p.beam * M2FT)
     const fresnelLower = points.map(p => (p.beam - p.r1) * M2FT)
@@ -207,7 +217,7 @@ export const ElevationProfile: ElevationProfileHook = {
       likely: d.likely || false
     }))
 
-    const allElevs = [...elevations, ...losLine, ...earthSurface]
+    const allElevs = [...elevations, ...losLine, ...earthSurface, ...(hasBuildings ? buildingTops : [])]
     let minY = Math.min(...allElevs) - 40
     let maxY = Math.max(...allElevs) + 120
 
@@ -248,6 +258,19 @@ export const ElevationProfile: ElevationProfileHook = {
             tension: 0.1,
             order: 4
           },
+          ...(hasBuildings ? [
+            {
+              label: "Buildings",
+              data: buildingTops,
+              borderColor: "#dc2626",
+              backgroundColor: "rgba(220, 38, 38, 0.45)",
+              fill: "-1",
+              pointRadius: 0,
+              borderWidth: 1,
+              tension: 0.1,
+              order: 3
+            }
+          ] : []),
           {
             label: "Line of Sight",
             data: losLine,

lib/microwaveprop_web/live/path_live.ex

@@ -4,6 +4,8 @@ defmodule MicrowavepropWeb.PathLive do
 
   import MicrowavepropWeb.Components.SkewTChart
 
+  alias Microwaveprop.Buildings.Index, as: BuildingsIndex
+  alias Microwaveprop.Buildings.Loader, as: BuildingsLoader
   alias Microwaveprop.Ionosphere
   alias Microwaveprop.Propagation
   alias Microwaveprop.Propagation.BandConfig
@@ -531,6 +533,10 @@ defmodule MicrowavepropWeb.PathLive do
     |> Map.put_new(:lat, lat)
     |> Map.put_new(:lon, lon)
     |> Map.put_new(:valid_time, valid_time)
+    |> Map.put_new(:min_refractivity_gradient, Map.get(cell, :native_min_gradient))
+    |> Map.put_new(:surface_refractivity, nil)
+    |> Map.put_new(:ducting_detected, Map.get(cell, :duct_count, 0) > 0)
+    |> Map.put_new(:duct_characteristics, nil)
   end
 
   # Linear interpolation along the great-circle-approximate path. Good
@@ -1622,14 +1628,18 @@ defmodule MicrowavepropWeb.PathLive do
   defp factor_name(:pressure), do: "Pressure"
 
   defp elevation_data(result) do
-    # ElevationProfile hook expects: points with dist_km, elev, beam, r1
+    raw_points = result.terrain.analysis.points
+    _ = BuildingsLoader.ensure_loaded_for_bbox(profile_bbox(raw_points))
+
+    # ElevationProfile hook expects: points with dist_km, elev, beam, r1, building_m
     points =
-      Enum.map(result.terrain.analysis.points, fn p ->
+      Enum.map(raw_points, fn p ->
         %{
           dist_km: p.dist_km,
           elev: p.elev,
           beam: p[:beam] || 0,
-          r1: p[:r1] || 0
+          r1: p[:r1] || 0,
+          building_m: BuildingsIndex.max_height_near(p.lat, p.lon, 80)
         }
       end)
 
@@ -1641,4 +1651,12 @@ defmodule MicrowavepropWeb.PathLive do
       ducts: []
     }
   end
+
+  defp profile_bbox([]), do: %{"south" => 0, "north" => 0, "west" => 0, "east" => 0}
+
+  defp profile_bbox(points) do
+    lats = Enum.map(points, & &1.lat)
+    lons = Enum.map(points, & &1.lon)
+    %{"south" => Enum.min(lats), "north" => Enum.max(lats), "west" => Enum.min(lons), "east" => Enum.max(lons)}
+  end
 end