perf: finish audit follow-ups (path conditions, recalibrator parallelism)

Path calculator conditions map was missing :latitude and
:best_duct_band_ghz. Scorer read them with bracket-notation so the
behaviour was defensively correct but we were leaving signal on the
floor:

- latitude: midpoint of src/dst so `score_season` picks up the right
  latitude-based seasonal shift for northern vs southern paths
- best_duct_band_ghz: queried via new Weather.nearest_native_duct_ghz/3
  at the midpoint so score_refractivity/4 applies the 1.15× boost
  when a native-resolution duct supports the target band

Recalibrator.fit/1 was serialising ~10k per-contact HRRR lookups
(5000 positives + 5000 negatives, one Weather.find_nearest_hrrr each).
Parallelised both sides with Task.async_stream at 20 concurrency —
well under the prod db pool of 30. Cuts a band recalibration from
~minutes of query round-trips to seconds.

lib/microwaveprop/propagation/recalibrator.ex

@@ -175,10 +175,23 @@ defmodule Microwaveprop.Propagation.Recalibrator do
 
     factor_band = band_mhz || 10_000
 
+    # Each contact_to_factors/2 calls `Weather.find_nearest_hrrr/3` —
+    # serial execution over ~5000 contacts burns a minute+ just on
+    # query round-trips. Parallelize at 20 concurrent queries, well
+    # under the :db pool size (30 in prod), so the recalibration
+    # finishes in seconds instead of minutes.
     factor_vectors =
       contacts
-      |> Enum.map(&contact_to_factors(&1, factor_band))
-      |> Enum.reject(&is_nil/1)
+      |> Task.async_stream(&contact_to_factors(&1, factor_band),
+        max_concurrency: 20,
+        timeout: 30_000,
+        on_timeout: :kill_task
+      )
+      |> Enum.flat_map(fn
+        {:ok, nil} -> []
+        {:ok, vec} -> [vec]
+        {:exit, _} -> []
+      end)
 
     {factor_vectors, contacts}
   end
@@ -201,13 +214,22 @@ defmodule Microwaveprop.Propagation.Recalibrator do
     factor_band = band_mhz || 10_000
 
     baselines
-    |> Enum.map(fn {lat, lon, time} ->
-      case Weather.find_nearest_hrrr(lat, lon, time) do
-        nil -> nil
-        profile -> compute_factors(profile, time, factor_band)
-      end
+    |> Task.async_stream(
+      fn {lat, lon, time} ->
+        case Weather.find_nearest_hrrr(lat, lon, time) do
+          nil -> nil
+          profile -> compute_factors(profile, time, factor_band)
+        end
+      end,
+      max_concurrency: 20,
+      timeout: 30_000,
+      on_timeout: :kill_task
+    )
+    |> Enum.flat_map(fn
+      {:ok, nil} -> []
+      {:ok, vec} -> [vec]
+      {:exit, _} -> []
     end)
-    |> Enum.reject(&is_nil/1)
   end
 
   defp run_training(positives, negatives, learning_rate, epochs) do

lib/microwaveprop/weather.ex

@@ -795,6 +795,45 @@ defmodule Microwaveprop.Weather do
     end
   end
 
+  @doc """
+  Returns the nearest `hrrr_native_profiles.best_duct_band_ghz` to
+  (`lat`, `lon`) at `timestamp`, or nil if no native profile covers
+  the cell at that time. Uses the same ±0.07° / ±1h tolerance as
+  HRRR pressure-level lookups.
+
+  The native product resolves thin trapping layers the pressure-level
+  product misses (see algo.md Part 2c), so this value is what the
+  refractivity scoring should consult when deciding whether to apply
+  the 1.15× native-duct boost.
+  """
+  @spec nearest_native_duct_ghz(float(), float(), DateTime.t()) :: float() | nil
+  def nearest_native_duct_ghz(lat, lon, %DateTime{} = timestamp) do
+    dlat = 0.07
+    dlon = 0.07
+    time_start = DateTime.add(timestamp, -3600, :second)
+    time_end = DateTime.add(timestamp, 3600, :second)
+
+    Repo.one(
+      from(h in HrrrNativeProfile,
+        where:
+          h.lat >= ^(lat - dlat) and h.lat <= ^(lat + dlat) and h.lon >= ^(lon - dlon) and h.lon <= ^(lon + dlon) and
+            h.valid_time >= ^time_start and h.valid_time <= ^time_end,
+        order_by:
+          fragment(
+            "ABS(? - ?) + ABS(? - ?) + ABS(EXTRACT(EPOCH FROM ? - ?))",
+            h.lat,
+            ^lat,
+            h.lon,
+            ^lon,
+            h.valid_time,
+            ^timestamp
+          ),
+        limit: 1,
+        select: h.best_duct_band_ghz
+      )
+    )
+  end
+
   @doc """
   Nearest sounding to (`lat`, `lon`) within `radius_km` km and a ±3-hour
   window around `timestamp`. Joins `weather_stations` to `soundings` so

lib/microwaveprop_web/live/path_live.ex

@@ -271,8 +271,15 @@ defmodule MicrowavepropWeb.PathLive do
       # surface ducts that sounding data resolves.
       sounding = build_sounding_readout(midlat, midlon, now)
 
+      # Native-resolution HRRR duct band near the midpoint. Resolves
+      # thin trapping layers HRRR's 13 pressure levels miss; feeds the
+      # 1.15× boost in Scorer.score_refractivity when the duct supports
+      # the target band.
+      native_duct_ghz = Weather.nearest_native_duct_ghz(midlat, midlon, now)
+
       # Build conditions and score
-      {conditions, scoring} = build_scoring(hrrr_profiles, src, now, band_config)
+      {conditions, scoring} =
+        build_scoring(hrrr_profiles, src, dst, now, band_config, native_duct_ghz)
 
       # Loss and power budgets
       loss_budget = compute_loss_budget(dist_km, freq_ghz, band_config, terrain_result, conditions)
@@ -436,9 +443,9 @@ defmodule MicrowavepropWeb.PathLive do
     end
   end
 
-  defp build_scoring([], _src, _now, _band_config), do: {nil, nil}
+  defp build_scoring([], _src, _dst, _now, _band_config, _native_duct_ghz), do: {nil, nil}
 
-  defp build_scoring(profiles, src, now, band_config) do
+  defp build_scoring(profiles, src, dst, now, band_config, native_duct_ghz) do
     temps = profiles |> Enum.map(& &1.surface_temp_c) |> Enum.reject(&is_nil/1)
     dewpoints = profiles |> Enum.map(& &1.surface_dewpoint_c) |> Enum.reject(&is_nil/1)
 
@@ -464,13 +471,15 @@ defmodule MicrowavepropWeb.PathLive do
         utc_hour: now.hour,
         utc_minute: now.minute,
         month: now.month,
+        latitude: (src.lat + dst.lat) / 2,
         longitude: src.lon,
         pressure_mb: if(pressures != [], do: Enum.min(pressures)),
         prev_pressure_mb: nil,
         rain_rate_mmhr: 0.0,
         min_refractivity_gradient: if(gradients != [], do: Enum.min(gradients)),
         bl_depth_m: if(bl_depths != [], do: Enum.sum(bl_depths) / length(bl_depths)),
-        pwat_mm: if(pwats != [], do: Enum.sum(pwats) / length(pwats))
+        pwat_mm: if(pwats != [], do: Enum.sum(pwats) / length(pwats)),
+        best_duct_band_ghz: native_duct_ghz
       }
 
       scoring = Scorer.composite_score(conditions, band_config)