Split HRRR pressure levels for grid hot path vs per-contact profiles

The skew-T commit (30c1018) doubled @pressure_levels from 13 to 25 so
new contact fetches would cover the full troposphere. That list is
also what PropagationGridWorker pulls per forecast hour, which
doubled the GRIB footprint (~57 MB compressed + 92k points × 25
levels × 3 vars decoded through wgrib2) and pushed prod pods over
their 4 Gi OOMKill threshold. Every chain died during f00 and the
map timeline never got beyond now and now+1h because the .ntms files
for f02-f18 were never written.

Split the constant:

  * @profile_pressure_levels (25 levels, 1000-100 mb) drives the
    per-contact HrrrClient.fetch_profile path so the skew-T plot
    keeps its full-atmosphere trace.

  * @grid_pressure_levels (13 levels, 1000-700 mb) drives the grid
    hot path. That's the band SoundingParams.derive reads for
    min_refractivity_gradient, and native hybrid-sigma data
    (native_min_gradient) takes priority over the pressure-level
    fallback anyway, so upper-air levels contribute nothing to
    scoring — pure memory waste on this path.

build_profile/1 still iterates the full 25-level list; grid fetches
simply populate the 13 near-surface slots and skip the rest.

Makes HrrrClient.pressure_messages public with a :grid | :profile
variant so the split is testable from outside the module.

lib/microwaveprop/weather/hrrr_client.ex

@@ -11,11 +11,10 @@ defmodule Microwaveprop.Weather.HrrrClient do
 
   defp hrrr_base, do: Application.get_env(:microwaveprop, :hrrr_base_url, @hrrr_base_default)
 
-  # Fine-grained levels below 900mb (~1km) for duct detection, plus standard upper levels.
-  # Every 25mb from 1000-900 for ~80m vertical spacing near surface. Above 700mb
-  # the spacing loosens to 50/100mb — enough vertical resolution for the
-  # contact-detail skew-T log-P plot without ballooning byte-range fetches.
-  @pressure_levels [
+  # Per-point profile fetches (contact detail + skew-T): full troposphere +
+  # lower stratosphere. 25 levels from 1000→100 mb — fine-grained near the
+  # surface for duct detection, loosening above 700 mb for the skew-T plot.
+  @profile_pressure_levels [
     1000,
     975,
     950,
@@ -43,6 +42,30 @@ defmodule Microwaveprop.Weather.HrrrClient do
     100
   ]
 
+  # Grid-wide fetches (PropagationGridWorker hot path): narrow to the
+  # near-surface band the scorer actually reads. `SoundingParams.derive`
+  # pulls `min_refractivity_gradient` from the lowest ~1 km, and native
+  # hybrid-sigma data (when present) takes priority for that metric
+  # anyway. Anything above 700 mb is dead weight that doubled the grid
+  # worker's peak memory when 92k points × levels × vars all decode
+  # through wgrib2 — enough to OOM the pod at 4 Gi. Keep the hot path
+  # on this slimmer list.
+  @grid_pressure_levels [
+    1000,
+    975,
+    950,
+    925,
+    900,
+    875,
+    850,
+    825,
+    800,
+    775,
+    750,
+    725,
+    700
+  ]
+
   @surface_messages [
     %{var: "TMP", level: "2 m above ground"},
     %{var: "DPT", level: "2 m above ground"},
@@ -205,8 +228,12 @@ defmodule Microwaveprop.Weather.HrrrClient do
     sfc_dpt_k = parsed["DPT:2 m above ground"]
     sfc_pres_pa = parsed["PRES:surface"]
 
+    # Iterate the full profile list so per-contact fetches that include
+    # upper-air data still populate the whole skew-T trace. Grid fetches
+    # only populate the 1000→700 mb subset (see @grid_pressure_levels);
+    # the other levels just produce empty slots that this loop skips.
     profile =
-      Enum.flat_map(@pressure_levels, fn level ->
+      Enum.flat_map(@profile_pressure_levels, fn level ->
         level_str = "#{level} mb"
         tmp = parsed["TMP:#{level_str}"]
         dpt = parsed["DPT:#{level_str}"]
@@ -258,7 +285,7 @@ defmodule Microwaveprop.Weather.HrrrClient do
     wanted =
       case product do
         :surface -> @surface_messages
-        :pressure -> pressure_messages()
+        :pressure -> pressure_messages(:profile)
       end
 
     Logger.info("HRRR fetching #{product} idx from #{idx_url}")
@@ -280,7 +307,7 @@ defmodule Microwaveprop.Weather.HrrrClient do
     wanted =
       case product do
         :surface -> @surface_messages
-        :pressure -> pressure_messages()
+        :pressure -> pressure_messages(:grid)
       end
 
     Logger.info("HRRR grid fetching #{product} idx from #{idx_url}")
@@ -321,8 +348,26 @@ defmodule Microwaveprop.Weather.HrrrClient do
     end
   end
 
-  defp pressure_messages do
-    for level <- @pressure_levels, var <- ["TMP", "DPT", "HGT"] do
+  @doc """
+  Pressure-level GRIB message descriptors for a fetch variant.
+
+    * `:grid` — narrow list of 13 levels (1000→700 mb) used by the
+      propagation grid hot path. Covers the ducting band without
+      ballooning the per-forecast-hour memory footprint.
+    * `:profile` — full 25 levels (1000→100 mb) used for per-contact
+      skew-T fetches.
+  """
+  @spec pressure_messages(:grid | :profile) :: [%{var: String.t(), level: String.t()}]
+  def pressure_messages(:grid) do
+    build_pressure_messages(@grid_pressure_levels)
+  end
+
+  def pressure_messages(:profile) do
+    build_pressure_messages(@profile_pressure_levels)
+  end
+
+  defp build_pressure_messages(levels) do
+    for level <- levels, var <- ["TMP", "DPT", "HGT"] do
       %{var: var, level: "#{level} mb"}
     end
   end

test/microwaveprop/weather/hrrr_client_test.exs

@@ -279,6 +279,66 @@ defmodule Microwaveprop.Weather.HrrrClientTest do
     end
   end
 
+  describe "pressure_messages/1" do
+    test ":grid returns only the near-surface levels needed for scoring" do
+      messages = HrrrClient.pressure_messages(:grid)
+
+      # 13 levels × 3 vars (TMP/DPT/HGT)
+      assert length(messages) == 39
+
+      levels =
+        messages
+        |> Enum.map(fn m ->
+          [num_str, _] = String.split(m.level, " ")
+          String.to_integer(num_str)
+        end)
+        |> Enum.uniq()
+        |> Enum.sort()
+
+      # Narrow list: 1000 → 700 mb, every 25 mb
+      assert Enum.max(levels) == 1000
+      assert Enum.min(levels) == 700
+      assert 700 in levels
+      assert 900 in levels
+
+      # Upper-air levels must be absent — they're the whole reason the grid
+      # worker OOMs when this function returns the full profile list.
+      refute 500 in levels
+      refute 300 in levels
+      refute 100 in levels
+    end
+
+    test ":profile returns full troposphere + lower stratosphere for the skew-T" do
+      messages = HrrrClient.pressure_messages(:profile)
+
+      # 25 levels × 3 vars
+      assert length(messages) == 75
+
+      levels =
+        messages
+        |> Enum.map(fn m ->
+          [num_str, _] = String.split(m.level, " ")
+          String.to_integer(num_str)
+        end)
+        |> Enum.uniq()
+        |> Enum.sort()
+
+      assert Enum.max(levels) == 1000
+      assert Enum.min(levels) == 100
+      assert 500 in levels
+      assert 300 in levels
+      assert 100 in levels
+    end
+
+    test ":grid and :profile both request TMP, DPT and HGT at every level" do
+      for variant <- [:grid, :profile] do
+        messages = HrrrClient.pressure_messages(variant)
+        vars = messages |> Enum.map(& &1.var) |> Enum.uniq() |> Enum.sort()
+        assert vars == ["DPT", "HGT", "TMP"]
+      end
+    end
+  end
+
   describe "surface_messages/0" do
     test "returns list of surface message descriptors" do
       messages = HrrrClient.surface_messages()