feat(grid-rs): Rust worker for HRRR f01..f18 propagation chain

Extracts the memory-hostile HRRR fetch → decode → score pipeline for
forecast hours 1–18 into a separate Rust service (`prop-grid-rs`).
Elixir retains f00 with its native-duct + NEXRAD + commercial-link
enrichment; Rust handles the other 18 steps per hourly chain.

Hand-off via a new `grid_tasks` table (`FOR UPDATE SKIP LOCKED` claim
from Rust, Postgrex `NOTIFY propagation_ready` back to Elixir). Rust
writes the same on-disk score-grid format Elixir already uses, to the
same `/data/scores` NFS tree. Phase 1 ships in shadow mode with
PROP_SCORES_DIR=/data/scores_shadow.

Rust crate layout at `rust/prop_grid_rs/` (1:1 module parity with the
Elixir source it ports):
  - grid, region, band_config, scores_file, sounding_params
  - scorer: all 10 factors + composite. Matches the Elixir scorer
    byte-for-byte across 115 golden-fixture samples (5 scenarios
    × 23 bands).
  - decoder: wgrib2 subprocess + Fortran-record lola-binary parser
  - fetcher: HRRR URL derivation + idx cache (1h TTL) + 8-way
    parallel byte-range downloads with 429/5xx retry
  - pipeline: end-to-end chain step, f00 rejected at the boundary
  - db: sqlx grid_tasks claim/complete + propagation_ready NOTIFY
  - bin/worker: tokio main loop, JSON logs, SIGTERM-safe

91 Rust tests + clippy -D warnings clean. 2,158 Elixir tests green.

Elixir additions:
  - `GridTaskEnqueuer` seeds fh=1..18 rows from
    `PropagationGridWorker.seed_chain/0`
  - `NotifyListener` LISTEN → warm `ScoreCache` → PubSub fan-out
  - `ShadowComparator` diffs prod vs shadow `.ntms` bodies
  - `mix rust.golden` task writes the Rust-side golden fixture

k8s: new `deployment-grid-rs.yaml` pinned to talos5 (32 GB NUC) via
`prop-grid-rs=primary` nodeSelector + `workload=grid-rs:NoSchedule`
toleration, 512 Mi limit, sharing the existing NFS `/data` mount.

The plan document is at `plans/vivid-hatching-quail.md` (local to my
workstation); phases 2 (cutover) and 3 (talos5 concurrency tuning)
follow after 72h of shadow-mode parity.

k8s/deployment-grid-rs.yaml

@@ -0,0 +1,94 @@
+apiVersion: apps/v1
+kind: Deployment
+metadata:
+  name: prop-grid-rs
+  namespace: prop
+  # Phase 1 (shadow) default: write to /data/scores_shadow so Elixir keeps
+  # owning the live /data/scores tree. Flip PROP_SCORES_DIR to /data/scores
+  # at cutover after ShadowComparator shows < 0.5 mean delta for 72h.
+spec:
+  replicas: 1
+  minReadySeconds: 5
+  strategy:
+    type: RollingUpdate
+    rollingUpdate:
+      maxSurge: 0
+      maxUnavailable: 1
+  selector:
+    matchLabels:
+      app: prop-grid-rs
+  template:
+    metadata:
+      labels:
+        app: prop-grid-rs
+        tier: grid-rs
+    spec:
+      # Pin to talos5 — the 32 GB NUC with NVMe. The worker peaks at ~500 Mi
+      # steady-state but benefits from local NVMe for the NFS scores-dir
+      # writes (faster fsync) and from never sharing the node with a hot
+      # Elixir pod. Label talos5 with `prop-grid-rs=primary` and taint it
+      # `workload=grid-rs:NoSchedule` to enforce this.
+      nodeSelector:
+        prop-grid-rs: "primary"
+      tolerations:
+        - key: workload
+          operator: Equal
+          value: grid-rs
+          effect: NoSchedule
+      imagePullSecrets:
+        - name: forgejo-registry
+      securityContext:
+        runAsUser: 65534
+        runAsNonRoot: true
+        fsGroup: 65534
+        seccompProfile:
+          type: RuntimeDefault
+      containers:
+        - name: prop-grid-rs
+          # Image built by a new CI pipeline from rust/prop_grid_rs/.
+          # Multi-arch (amd64 + arm64) — reuses the repo's existing
+          # buildx wiring.
+          image: git.mcintire.me/graham/prop-grid-rs:main
+          imagePullPolicy: IfNotPresent
+          env:
+            # Elixir secrets bundle carries DATABASE_URL already. Rust
+            # reads it directly (sqlx connects with the same URL).
+            - name: HRRR_BASE_URL
+              value: "http://skippy.w5isp.com:8080"
+            - name: PROP_SCORES_DIR
+              value: "/data/scores_shadow"
+            - name: RUST_LOG
+              value: "info"
+            - name: PROP_GRID_RS_PG_CONNS
+              value: "4"
+          envFrom:
+            - secretRef:
+                name: prop-secrets
+          # No HTTP surface. Liveness is "the process is still running";
+          # let the kubelet restart us if we crash. Claiming work from
+          # grid_tasks is the implicit readiness signal — an idle pod is
+          # still healthy (the queue is simply empty).
+          resources:
+            requests:
+              cpu: 100m
+              memory: 128Mi
+            limits:
+              cpu: "4"
+              memory: 512Mi
+          securityContext:
+            allowPrivilegeEscalation: false
+            runAsNonRoot: true
+            runAsUser: 65534
+            capabilities:
+              drop:
+                - ALL
+            seccompProfile:
+              type: RuntimeDefault
+          volumeMounts:
+            - name: data
+              mountPath: /data
+      volumes:
+        - name: data
+          nfs:
+            server: 10.0.15.103
+            path: /data

k8s/kustomization.yaml

@@ -8,5 +8,6 @@ resources:
   - rbac.yaml
   - deployment.yaml
   - deployment-backfill.yaml
+  - deployment-grid-rs.yaml
   - service.yaml
   - metrics-service.yaml

lib/microwaveprop/propagation/grid_task_enqueuer.ex

@@ -0,0 +1,60 @@
+defmodule Microwaveprop.Propagation.GridTaskEnqueuer do
+  @moduledoc """
+  Seeds `grid_tasks` rows for the Rust `prop-grid-rs` worker.
+
+  Called from `PropagationGridWorker.seed_chain/0` alongside the existing
+  Elixir f00..f18 Oban fan-out. Rust only claims rows with
+  `forecast_hour > 0`; Elixir still owns the f00 analysis-hour chain
+  because of native-duct + NEXRAD + commercial-link enrichment.
+
+  Inserts are idempotent via the `(run_time, forecast_hour)` unique
+  index — re-seeding the same cycle is a no-op.
+  """
+
+  alias Microwaveprop.Repo
+
+  require Logger
+
+  @max_forecast_hour 18
+
+  @spec seed(DateTime.t()) :: {:ok, non_neg_integer()} | {:error, term()}
+  def seed(%DateTime{} = run_time) do
+    run_time = DateTime.truncate(run_time, :second)
+    now = DateTime.truncate(DateTime.utc_now(), :microsecond)
+
+    rows =
+      for fh <- 1..@max_forecast_hour do
+        %{
+          id: Ecto.UUID.bingenerate(),
+          run_time: run_time,
+          forecast_hour: fh,
+          valid_time: DateTime.add(run_time, fh * 3600, :second),
+          status: "queued",
+          attempt: 0,
+          claimed_at: nil,
+          completed_at: nil,
+          error: nil,
+          inserted_at: now,
+          updated_at: now
+        }
+      end
+
+    {count, _} =
+      Repo.insert_all("grid_tasks", rows,
+        on_conflict: :nothing,
+        conflict_target: [:run_time, :forecast_hour]
+      )
+
+    if count > 0 do
+      Logger.info("GridTaskEnqueuer: seeded #{count} grid_tasks for run_time=#{run_time}")
+    else
+      Logger.info("GridTaskEnqueuer: run_time=#{run_time} already seeded")
+    end
+
+    {:ok, count}
+  rescue
+    e ->
+      Logger.error("GridTaskEnqueuer: seed failed: #{inspect(e)}")
+      {:error, e}
+  end
+end

lib/microwaveprop/propagation/notify_listener.ex

@@ -0,0 +1,100 @@
+defmodule Microwaveprop.Propagation.NotifyListener do
+  @moduledoc """
+  Listens for `NOTIFY propagation_ready '<iso valid_time>'` from the Rust
+  `prop-grid-rs` worker. When a notification arrives, warms
+  `ScoreCache` for every band at that `valid_time` (reading from the
+  shared NFS `/data/scores/<band>/<iso>.ntms` tree that Rust just
+  wrote) and fans out the standard `"propagation:updated"` PubSub so
+  LiveView clients refresh without polling.
+
+  No-op under `testing: :inline` Oban / when the Postgrex.Notifications
+  supervisor isn't started — the listener is additive; shadow mode and
+  unit tests don't need it running.
+  """
+
+  use GenServer
+
+  alias Microwaveprop.Propagation
+  alias Microwaveprop.Propagation.BandConfig
+  alias Microwaveprop.Propagation.ScoreCache
+  alias Microwaveprop.Repo
+
+  require Logger
+
+  @channel "propagation_ready"
+  @pubsub Microwaveprop.PubSub
+  @topic "propagation:updated"
+
+  @spec start_link(keyword()) :: GenServer.on_start()
+  def start_link(opts) do
+    GenServer.start_link(__MODULE__, opts, name: __MODULE__)
+  end
+
+  @impl true
+  def init(_opts) do
+    send(self(), :subscribe)
+    {:ok, %{ref: nil, pid: nil}}
+  end
+
+  @impl true
+  def handle_info(:subscribe, state) do
+    case start_notifications_conn() do
+      {:ok, pid, ref} ->
+        {:noreply, %{state | pid: pid, ref: ref}}
+
+      {:error, reason} ->
+        Logger.warning("NotifyListener: failed to subscribe to #{@channel}: #{inspect(reason)}")
+        # Retry in 30s. An unreachable DB at boot shouldn't wedge the
+        # supervisor tree.
+        Process.send_after(self(), :subscribe, 30_000)
+        {:noreply, state}
+    end
+  end
+
+  @impl true
+  def handle_info({:notification, _pid, _ref, @channel, payload}, state) do
+    case DateTime.from_iso8601(payload) do
+      {:ok, valid_time, _} ->
+        handle_propagation_ready(valid_time)
+
+      _ ->
+        Logger.warning("NotifyListener: malformed #{@channel} payload: #{inspect(payload)}")
+    end
+
+    {:noreply, state}
+  end
+
+  def handle_info(_msg, state), do: {:noreply, state}
+
+  defp start_notifications_conn do
+    config = Application.fetch_env!(:microwaveprop, Repo)
+
+    case Postgrex.Notifications.start_link(config) do
+      {:ok, pid} ->
+        case Postgrex.Notifications.listen(pid, @channel) do
+          {:ok, ref} ->
+            {:ok, pid, ref}
+
+          other ->
+            {:error, other}
+        end
+
+      other ->
+        other
+    end
+  end
+
+  defp handle_propagation_ready(valid_time) do
+    Enum.each(BandConfig.all_bands(), fn band ->
+      Propagation.warm_cache_and_broadcast(band.freq_mhz, valid_time)
+    end)
+
+    # Prune anything older than 2 hours so the cache doesn't grow
+    # unbounded when Rust covers many forecast hours back-to-back.
+    ScoreCache.prune_older_than(DateTime.add(DateTime.utc_now(), -2, :hour))
+
+    Phoenix.PubSub.broadcast(@pubsub, @topic, {:propagation_updated, [valid_time]})
+
+    Logger.info("NotifyListener: warmed ScoreCache + broadcast for valid_time=#{valid_time}")
+  end
+end

lib/microwaveprop/propagation/shadow_comparator.ex

@@ -0,0 +1,119 @@
+defmodule Microwaveprop.Propagation.ShadowComparator do
+  @moduledoc """
+  Shadow-mode validator for the Rust `prop-grid-rs` port.
+
+  During Phase 1 shadow mode the Rust worker writes score-grid files to
+  `/data/scores_shadow/<band>/<iso>.ntms` while Elixir keeps writing to
+  `/data/scores/`. This module compares the two files and logs the
+  per-band delta distribution so drift is visible before cutover.
+
+  Callable from IEx on demand or from a one-shot Mix task; not started
+  in the supervision tree (this is temporary instrumentation).
+  """
+
+  alias Microwaveprop.Propagation.ScoresFile
+
+  require Logger
+
+  @default_prod_dir "/data/scores"
+  @default_shadow_dir "/data/scores_shadow"
+
+  @type diff :: %{
+          band_mhz: non_neg_integer(),
+          valid_time: DateTime.t(),
+          total_cells: non_neg_integer(),
+          matching_cells: non_neg_integer(),
+          missing_shadow_cells: non_neg_integer(),
+          max_abs_delta: non_neg_integer(),
+          mean_abs_delta: float()
+        }
+
+  @spec compare(non_neg_integer(), DateTime.t(), keyword()) ::
+          {:ok, diff()} | {:error, term()}
+  def compare(band_mhz, %DateTime{} = valid_time, opts \\ []) do
+    prod_dir = Keyword.get(opts, :prod_dir, @default_prod_dir)
+    shadow_dir = Keyword.get(opts, :shadow_dir, @default_shadow_dir)
+
+    with {:ok, prod} <- read_file(prod_dir, band_mhz, valid_time),
+         {:ok, shadow} <- read_file(shadow_dir, band_mhz, valid_time) do
+      {:ok, diff_payloads(band_mhz, valid_time, prod, shadow)}
+    end
+  end
+
+  defp read_file(dir, band_mhz, valid_time) do
+    path = band_mhz |> ScoresFile.path_for(valid_time) |> swap_base(dir)
+
+    case File.read(path) do
+      {:ok, binary} -> decode_scores_file(binary)
+      {:error, reason} -> {:error, {:read, path, reason}}
+    end
+  end
+
+  defp swap_base(path, new_base) do
+    suffix = Path.relative_to(path, ScoresFile.base_dir())
+    Path.join(new_base, suffix)
+  end
+
+  # Inline parse of the v1 scores-file on-disk format so this module
+  # doesn't reach into `ScoresFile`'s private `decode/1`. The format is
+  # documented in `ScoresFile`'s moduledoc; only the body size and
+  # dimensions matter for a diff, so we intentionally keep this minimal.
+  # The literal "NTMS" magic is the file-header marker already on disk.
+  defp decode_scores_file(
+         <<"NTMS", 1::unsigned-8, _band_mhz::unsigned-little-32, _valid_time_unix::signed-little-64,
+           _lat_min::float-little-32, _lon_min::float-little-32, _step::float-little-32, n_rows::unsigned-little-16,
+           n_cols::unsigned-little-16, body::binary>>
+       ) do
+    expected = n_rows * n_cols
+
+    if byte_size(body) == expected do
+      {:ok, %{n_rows: n_rows, n_cols: n_cols, scores: body}}
+    else
+      {:error, :invalid_format}
+    end
+  end
+
+  defp decode_scores_file(_), do: {:error, :invalid_format}
+
+  defp diff_payloads(band_mhz, valid_time, prod, shadow) do
+    %{scores: p_body, n_cols: n_cols, n_rows: n_rows} = prod
+    %{scores: s_body} = shadow
+
+    {total, matching, missing, max_abs, sum_abs} =
+      for row <- 0..(n_rows - 1),
+          col <- 0..(n_cols - 1),
+          reduce: {0, 0, 0, 0, 0} do
+        {t, m, miss, max_d, sum_d} ->
+          idx = row * n_cols + col
+          p = :binary.at(p_body, idx)
+          s = :binary.at(s_body, idx)
+
+          cond do
+            p == 255 and s == 255 ->
+              {t, m, miss, max_d, sum_d}
+
+            p != 255 and s == 255 ->
+              {t + 1, m, miss + 1, max_d, sum_d}
+
+            p == s ->
+              {t + 1, m + 1, miss, max_d, sum_d}
+
+            true ->
+              d = abs(p - s)
+              {t + 1, m, miss, max(max_d, d), sum_d + d}
+          end
+      end
+
+    mean = if total > 0, do: sum_abs / total, else: 0.0
+
+    %{
+      band_mhz: band_mhz,
+      valid_time: valid_time,
+      total_cells: total,
+      matching_cells: matching,
+      missing_shadow_cells: missing,
+      max_abs_delta: max_abs,
+      mean_abs_delta: mean
+    }
+  end
+end

lib/microwaveprop/workers/propagation_grid_worker.ex

@@ -45,6 +45,7 @@ defmodule Microwaveprop.Workers.PropagationGridWorker do
   alias Microwaveprop.Propagation
   alias Microwaveprop.Propagation.BandConfig
   alias Microwaveprop.Propagation.Grid
+  alias Microwaveprop.Propagation.GridTaskEnqueuer
   alias Microwaveprop.Propagation.ProfilesFile
   alias Microwaveprop.Propagation.ScoreCache
   alias Microwaveprop.Weather
@@ -96,6 +97,15 @@ defmodule Microwaveprop.Workers.PropagationGridWorker do
       end
 
     Oban.insert_all(jobs)
+
+    # Seed the grid_tasks table in parallel so the Rust `prop-grid-rs`
+    # worker can pick up f01..f18 from a shared NFS mount. During Phase
+    # 1 shadow mode this runs alongside the Elixir chain; the Rust
+    # writes land in /data/scores_shadow and are diffed by
+    # `ShadowComparator`. At cutover the Elixir fan-out above is
+    # trimmed to just fh=0.
+    _ = GridTaskEnqueuer.seed(run_time)
+
     :ok
   end
 

lib/mix/tasks/rust.golden.ex

@@ -0,0 +1,214 @@
+defmodule Mix.Tasks.Rust.Golden do
+  @shortdoc "Generate golden test fixtures for the Rust scorer port"
+  @moduledoc """
+  Dump Elixir-scorer output for a sample of points to
+  `priv/rust_golden/scores.bincode`. The Rust crate loads this fixture
+  in its scorer tests to assert byte-for-byte parity with the Elixir
+  implementation.
+
+  The fixture format is a little-endian binary:
+
+      n_samples       : u32
+      per-sample:
+        abs_humidity      : f64
+        temp_f            : f64
+        dewpoint_f        : f64
+        wind_speed_kts    : f64 (NaN = None)
+        sky_cover_pct     : f64 (NaN = None)
+        utc_hour          : u8
+        utc_minute        : u8
+        month             : u8
+        longitude         : f64
+        latitude          : f64   (NaN = None)
+        pressure_mb       : f64   (NaN = None)
+        prev_pressure_mb  : f64   (NaN = None)
+        rain_rate_mmhr    : f64   (NaN = None)
+        min_refractivity_gradient : f64 (NaN = None)
+        bl_depth_m        : f64   (NaN = None)
+        pwat_mm           : f64   (NaN = None)
+        best_duct_band_ghz: f64   (NaN = None)
+        bulk_richardson   : f64   (NaN = None)
+        band_mhz          : u32
+        expected_score    : i32
+
+  No Rust dependency on bincode's stable format — we write fixed-width
+  fields in a fixed order and the Rust loader reads them in the same
+  order. Matches the Rust `Conditions` struct field-for-field.
+
+      mix rust.golden             # writes priv/rust_golden/scores.bincode
+      mix rust.golden --print 5   # pretty-print first 5 samples
+
+  """
+  use Mix.Task
+
+  alias Microwaveprop.Propagation.BandConfig
+  alias Microwaveprop.Propagation.Scorer
+
+  @impl true
+  def run(args) do
+    {opts, _, _} = OptionParser.parse(args, strict: [print: :integer])
+    samples = build_samples()
+
+    path = Path.join(["priv", "rust_golden", "scores.bincode"])
+    File.mkdir_p!(Path.dirname(path))
+    File.write!(path, encode(samples))
+    Mix.shell().info("wrote #{length(samples)} samples to #{path}")
+
+    if n = opts[:print] do
+      samples |> Enum.take(n) |> Enum.each(&IO.inspect/1)
+    end
+  end
+
+  defp build_samples do
+    bands = BandConfig.all_bands()
+
+    conditions_set = [
+      summer_peak(),
+      winter_dry_cold(),
+      stormy_afternoon(),
+      dawn_duct(),
+      humid_gulf()
+    ]
+
+    for {c, idx} <- Enum.with_index(conditions_set), band <- bands do
+      result = Scorer.composite_score(c, band)
+      {idx, c, band.freq_mhz, result.score}
+    end
+  end
+
+  defp summer_peak do
+    %{
+      abs_humidity: 10.0,
+      temp_f: 80,
+      dewpoint_f: 70,
+      wind_speed_kts: 5,
+      sky_cover_pct: 20,
+      utc_hour: 11,
+      utc_minute: 15,
+      month: 6,
+      longitude: -75.0,
+      pressure_mb: 1020,
+      prev_pressure_mb: 1018,
+      rain_rate_mmhr: 0,
+      min_refractivity_gradient: -350,
+      bl_depth_m: 400,
+      pwat_mm: 25.0
+    }
+  end
+
+  defp winter_dry_cold do
+    %{
+      abs_humidity: 2.5,
+      temp_f: 28,
+      dewpoint_f: 14,
+      wind_speed_kts: 18,
+      sky_cover_pct: 10,
+      utc_hour: 14,
+      utc_minute: 0,
+      month: 1,
+      longitude: -97.0,
+      pressure_mb: 1028,
+      prev_pressure_mb: 1026,
+      rain_rate_mmhr: 0,
+      min_refractivity_gradient: -60,
+      bl_depth_m: 1800,
+      pwat_mm: 5.0
+    }
+  end
+
+  defp stormy_afternoon do
+    %{
+      abs_humidity: 18.0,
+      temp_f: 85,
+      dewpoint_f: 74,
+      wind_speed_kts: 22,
+      sky_cover_pct: 95,
+      utc_hour: 21,
+      utc_minute: 0,
+      month: 7,
+      longitude: -97.0,
+      pressure_mb: 1002,
+      prev_pressure_mb: 1008,
+      rain_rate_mmhr: 8.0,
+      min_refractivity_gradient: -80,
+      bl_depth_m: 2200,
+      pwat_mm: 38.0
+    }
+  end
+
+  defp dawn_duct do
+    %{
+      abs_humidity: 14.0,
+      temp_f: 72,
+      dewpoint_f: 70,
+      wind_speed_kts: 3,
+      sky_cover_pct: 5,
+      utc_hour: 11,
+      utc_minute: 30,
+      month: 5,
+      longitude: -95.0,
+      pressure_mb: 1018,
+      prev_pressure_mb: 1017,
+      rain_rate_mmhr: 0,
+      min_refractivity_gradient: -220,
+      bl_depth_m: 140,
+      pwat_mm: 30.0
+    }
+  end
+
+  defp humid_gulf do
+    %{
+      abs_humidity: 22.0,
+      temp_f: 88,
+      dewpoint_f: 77,
+      wind_speed_kts: 8,
+      sky_cover_pct: 55,
+      utc_hour: 18,
+      utc_minute: 0,
+      month: 8,
+      longitude: -93.0,
+      latitude: 29.5,
+      pressure_mb: 1014,
+      prev_pressure_mb: 1014,
+      rain_rate_mmhr: 0,
+      min_refractivity_gradient: -110,
+      bl_depth_m: 700,
+      pwat_mm: 52.0
+    }
+  end
+
+  defp encode(samples) do
+    header = <<length(samples)::unsigned-little-32>>
+    body = for {_idx, c, band_mhz, score} <- samples, into: <<>>, do: encode_sample(c, band_mhz, score)
+    header <> body
+  end
+
+  defp encode_sample(c, band_mhz, score) do
+    f(c.abs_humidity) <>
+      f(c.temp_f) <>
+      f(c.dewpoint_f) <>
+      opt(c[:wind_speed_kts]) <>
+      opt(c[:sky_cover_pct]) <>
+      <<c.utc_hour::unsigned-8, c.utc_minute::unsigned-8, c.month::unsigned-8>> <>
+      f(c.longitude) <>
+      opt(c[:latitude]) <>
+      opt(c[:pressure_mb]) <>
+      opt(c[:prev_pressure_mb]) <>
+      opt(c[:rain_rate_mmhr]) <>
+      opt(c[:min_refractivity_gradient]) <>
+      opt(c[:bl_depth_m]) <>
+      opt(c[:pwat_mm]) <>
+      opt(c[:best_duct_band_ghz]) <>
+      opt(c[:bulk_richardson]) <>
+      <<band_mhz::unsigned-little-32, score::signed-little-32>>
+  end
+
+  # IEEE 754 quiet-NaN bit pattern, little-endian. Used as the sentinel
+  # for `None` on the Rust side — `f64::is_nan` → `Option::None`.
+  @nan_bytes <<0x7FF8_0000_0000_0000::unsigned-little-64>>
+
+  defp f(n) when is_float(n), do: <<n::float-little-64>>
+  defp f(n) when is_integer(n), do: <<n * 1.0::float-little-64>>
+  defp opt(nil), do: @nan_bytes
+  defp opt(v), do: f(v)
+end

priv/repo/migrations/20260419151243_create_grid_tasks.exs

@@ -0,0 +1,48 @@
+defmodule Microwaveprop.Repo.Migrations.CreateGridTasks do
+  use Ecto.Migration
+
+  def change do
+    # Hand-off queue between Elixir's PropagationGridWorker (seed) and the
+    # external Rust `prop-grid-rs` worker. Each row is one forecast hour's
+    # worth of fetch → decode → score → write-ntms work. Rust claims with
+    # `SELECT ... FOR UPDATE SKIP LOCKED` on (status='queued'), marks
+    # 'running' while working, and transitions to 'done' / 'failed' on
+    # completion. On 'done' it NOTIFYs `propagation_ready` so Elixir pods
+    # can warm ScoreCache without polling.
+    create table(:grid_tasks, primary_key: false) do
+      add :id, :binary_id, primary_key: true
+
+      # HRRR cycle + step. (run_time, forecast_hour) is the natural key; an
+      # hourly cron re-enqueueing the same step is a no-op via the unique
+      # index rather than a conflict that has to be handled.
+      add :run_time, :utc_datetime, null: false
+      add :forecast_hour, :integer, null: false
+      add :valid_time, :utc_datetime, null: false
+
+      # 'queued' → 'running' → 'done' | 'failed'. Not an enum so we can add
+      # more states later without a migration.
+      add :status, :string, null: false, default: "queued"
+
+      # How many times a worker has claimed this row. Incremented on each
+      # claim so runaway retries are observable without scanning logs.
+      add :attempt, :integer, null: false, default: 0
+
+      add :claimed_at, :utc_datetime_usec
+      add :completed_at, :utc_datetime_usec
+      add :error, :text
+
+      timestamps(type: :utc_datetime)
+    end
+
+    # Uniqueness on the natural key lets the seeder run `INSERT ... ON CONFLICT
+    # DO NOTHING` and stay idempotent across retries of the seed job.
+    create unique_index(:grid_tasks, [:run_time, :forecast_hour])
+
+    # Rust's claim query filters on status first. A partial index on just the
+    # claimable subset keeps the common lookup cheap as finished rows
+    # accumulate — the table stays small (19 rows per hour, pruned on a cron)
+    # but the principle is cheap either way.
+    create index(:grid_tasks, [:status], where: "status = 'queued'", name: :grid_tasks_queued_idx)
+    create index(:grid_tasks, [:completed_at])
+  end
+end

rust/prop_grid_rs/.gitignore

@@ -0,0 +1 @@
+target/

rust/prop_grid_rs/Cargo.toml

@@ -0,0 +1,36 @@
+[package]
+name = "prop_grid_rs"
+version = "0.1.0"
+edition = "2021"
+publish = false
+
+[lib]
+name = "prop_grid_rs"
+path = "src/lib.rs"
+
+[[bin]]
+name = "worker"
+path = "src/bin/worker.rs"
+
+[dependencies]
+tokio = { version = "1", features = ["full"] }
+sqlx = { version = "0.8", features = ["runtime-tokio-rustls", "postgres", "uuid", "chrono", "macros"] }
+reqwest = { version = "0.12", features = ["rustls-tls", "stream"], default-features = false }
+bytes = "1"
+anyhow = "1"
+thiserror = "2"
+tracing = "0.1"
+tracing-subscriber = { version = "0.3", features = ["env-filter", "json"] }
+chrono = { version = "0.4", features = ["serde"] }
+uuid = { version = "1", features = ["v4", "serde"] }
+serde = { version = "1", features = ["derive"] }
+serde_json = "1"
+bincode = "1.3"
+num_cpus = "1"
+byteorder = "1"
+futures = "0.3"
+
+[dev-dependencies]
+tokio = { version = "1", features = ["full", "test-util"] }
+pretty_assertions = "1"
+tempfile = "3"

rust/prop_grid_rs/Dockerfile

@@ -0,0 +1,33 @@
+# syntax=docker/dockerfile:1.7
+#
+# Multi-arch build for `prop-grid-rs`. wgrib2 is installed from Debian
+# Trixie (same version the Elixir image uses). The binary runs as a
+# non-root uid that matches the fsGroup on the NFS scores mount.
+FROM rust:1.94-trixie AS builder
+WORKDIR /src
+
+# Cache deps: copy manifests first so dependency changes alone don't
+# invalidate the source-layer cache.
+COPY Cargo.toml Cargo.lock* ./
+RUN mkdir -p src src/bin \
+ && echo 'fn main() {}' > src/bin/worker.rs \
+ && echo '' > src/lib.rs \
+ && cargo build --release --bin worker \
+ && rm -rf src
+
+COPY src ./src
+RUN cargo build --release --bin worker
+
+# Runtime image: slim debian plus wgrib2. libexpat/libjasper pulled in
+# transitively by wgrib2 for PNG/JPEG2000 GRIB2 decompression.
+FROM debian:trixie-slim AS runtime
+RUN apt-get update && apt-get install -y --no-install-recommends \
+      wgrib2 \
+      ca-certificates \
+      tini \
+ && rm -rf /var/lib/apt/lists/*
+
+COPY --from=builder /src/target/release/worker /usr/local/bin/prop-grid-rs
+
+USER 65534:65534
+ENTRYPOINT ["/usr/bin/tini", "--", "/usr/local/bin/prop-grid-rs"]

rust/prop_grid_rs/src/band_config.rs

@@ -0,0 +1,483 @@
+//! Band configuration tables. 1:1 port of
+//! `lib/microwaveprop/propagation/band_config.ex`.
+//!
+//! Keep the data layout identical to the Elixir module; any numerical
+//! drift here will show up immediately in golden-fixture scorer tests.
+
+use std::sync::OnceLock;
+
+#[derive(Debug, Clone, Copy, PartialEq, Eq)]
+pub enum HumidityEffect {
+    Beneficial,
+    Harmful,
+}
+
+#[derive(Debug, Clone, Copy)]
+pub struct Weights {
+    pub humidity: f64,
+    pub time_of_day: f64,
+    pub td_depression: f64,
+    pub refractivity: f64,
+    pub sky: f64,
+    pub season: f64,
+    pub wind: f64,
+    pub rain: f64,
+    pub pressure: f64,
+    pub pwat: f64,
+}
+
+impl Weights {
+    #[allow(clippy::too_many_arguments)]
+    pub const fn new(
+        humidity: f64,
+        time_of_day: f64,
+        td_depression: f64,
+        refractivity: f64,
+        sky: f64,
+        season: f64,
+        wind: f64,
+        rain: f64,
+        pressure: f64,
+        pwat: f64,
+    ) -> Self {
+        Self {
+            humidity,
+            time_of_day,
+            td_depression,
+            refractivity,
+            sky,
+            season,
+            wind,
+            rain,
+            pressure,
+            pwat,
+        }
+    }
+}
+
+/// Default weight vector fit by gradient descent on 5,000 QSOs
+/// (2026-04-11). Used as fallback for bands that don't carry a `weights`
+/// override.
+pub const DEFAULT_WEIGHTS: Weights = Weights::new(
+    0.1243, // humidity
+    0.0496, // time_of_day
+    0.0978, // td_depression
+    0.1049, // refractivity
+    0.08,   // sky
+    0.1112, // season
+    0.08,   // wind
+    0.1362, // rain
+    0.1032, // pressure
+    0.1128, // pwat
+);
+
+/// Sunrise hour by month (1..=12) in local solar time. Index = month - 1.
+pub const SUNRISE_TABLE: [f64; 12] = [
+    7.4, 7.3, 7.0, 6.7, 6.35, 6.25, 6.35, 6.65, 6.9, 7.1, 7.35, 7.45,
+];
+
+pub const HUMIDITY_BENEFICIAL_THRESHOLDS: &[(u8, i32)] = &[
+    (4, 55),
+    (7, 70),
+    (10, 82),
+    (14, 90),
+    (18, 95),
+    (22, 88),
+];
+pub const HUMIDITY_BENEFICIAL_DEFAULT: i32 = 75;
+
+/// `(gradient_max, score_beneficial, score_harmful)`. First entry whose
+/// `gradient_max` exceeds the observed gradient wins. Calibrated for
+/// HRRR-derived gradients.
+pub const REFRACTIVITY_THRESHOLDS: &[(i32, i32, i32)] = &[
+    (-200, 98, 85),
+    (-150, 92, 80),
+    (-100, 82, 72),
+    (-75, 68, 62),
+    (-55, 55, 55),
+    (-40, 48, 48),
+];
+pub const REFRACTIVITY_DEFAULT: (i32, i32) = (42, 42);
+
+#[derive(Debug, Clone)]
+pub struct BandConfig {
+    pub freq_mhz: u32,
+    pub label: &'static str,
+    pub o2_db_km: f64,
+    pub h2o_coeff: f64,
+    pub humidity_effect: HumidityEffect,
+    pub humidity_penalty: f64,
+    pub rain_k: f64,
+    pub rain_alpha: f64,
+    /// Per-month base score for seasonal factor, index = month - 1.
+    pub seasonal_base: [i32; 12],
+    /// Per-month additive adjustment, index = month - 1.
+    pub seasonal_adj: [i32; 12],
+    pub typical_range_km: u32,
+    pub extended_range_km: u32,
+    pub exceptional_range_km: u32,
+    /// `None` falls back to `DEFAULT_WEIGHTS`.
+    pub weights: Option<Weights>,
+}
+
+impl BandConfig {
+    pub fn weights(&self) -> Weights {
+        self.weights.unwrap_or(DEFAULT_WEIGHTS)
+    }
+}
+
+/// Fixed-size literal helper; month values given as (month, score) pairs
+/// in Elixir map form. Panics at construction if a month is out of range.
+const fn months(v: [(u8, i32); 12]) -> [i32; 12] {
+    // Build by iterating; can't use const fn loop with indirect writes
+    // cleanly, so use a match per position.
+    let mut out = [0; 12];
+    let mut i = 0;
+    while i < 12 {
+        let (m, s) = v[i];
+        // Month values always 1..=12, stored at index month - 1 is the
+        // convention in Elixir — we rely on the literal being in month
+        // order here (it is in every band config).
+        assert!(m >= 1 && m <= 12);
+        out[(m - 1) as usize] = s;
+        i += 1;
+    }
+    out
+}
+
+const fn adj_from(values: &[(u8, i32)]) -> [i32; 12] {
+    let mut out = [0; 12];
+    let mut i = 0;
+    while i < values.len() {
+        let (m, s) = values[i];
+        assert!(m >= 1 && m <= 12);
+        out[(m - 1) as usize] = s;
+        i += 1;
+    }
+    out
+}
+
+// The seasonal_base tables are identical across many bands; pull out the
+// common shape once so the 22 band definitions stay scannable.
+const BASE_LOW_BAND: [i32; 12] = months([
+    (1, 38), (2, 40), (3, 22), (4, 55), (5, 68), (6, 90),
+    (7, 95), (8, 75), (9, 78), (10, 88), (11, 78), (12, 25),
+]);
+
+const BASE_50: [i32; 12] = months([
+    (1, 30), (2, 32), (3, 25), (4, 50), (5, 70), (6, 95),
+    (7, 95), (8, 70), (9, 65), (10, 70), (11, 60), (12, 25),
+]);
+
+const BASE_24G: [i32; 12] = months([
+    (1, 88), (2, 84), (3, 68), (4, 62), (5, 51), (6, 34),
+    (7, 18), (8, 18), (9, 48), (10, 68), (11, 96), (12, 88),
+]);
+
+const BASE_47G: [i32; 12] = months([
+    (1, 90), (2, 88), (3, 78), (4, 68), (5, 55), (6, 38),
+    (7, 22), (8, 22), (9, 48), (10, 74), (11, 96), (12, 90),
+]);
+
+const BASE_68G: [i32; 12] = months([
+    (1, 90), (2, 88), (3, 78), (4, 65), (5, 50), (6, 32),
+    (7, 18), (8, 18), (9, 44), (10, 70), (11, 92), (12, 90),
+]);
+
+const BASE_75G: [i32; 12] = months([
+    (1, 90), (2, 90), (3, 80), (4, 68), (5, 55), (6, 38),
+    (7, 22), (8, 22), (9, 48), (10, 74), (11, 96), (12, 90),
+]);
+
+const BASE_122G: [i32; 12] = months([
+    (1, 92), (2, 90), (3, 78), (4, 62), (5, 45), (6, 28),
+    (7, 15), (8, 15), (9, 38), (10, 68), (11, 92), (12, 92),
+]);
+
+const BASE_134G: [i32; 12] = months([
+    (1, 92), (2, 90), (3, 78), (4, 65), (5, 48), (6, 30),
+    (7, 18), (8, 18), (9, 42), (10, 70), (11, 92), (12, 92),
+]);
+
+const BASE_142G: [i32; 12] = months([
+    (1, 92), (2, 90), (3, 78), (4, 65), (5, 47), (6, 28),
+    (7, 16), (8, 16), (9, 40), (10, 68), (11, 92), (12, 92),
+]);
+
+const BASE_145G: [i32; 12] = months([
+    (1, 92), (2, 90), (3, 78), (4, 64), (5, 46), (6, 27),
+    (7, 15), (8, 15), (9, 38), (10, 66), (11, 92), (12, 92),
+]);
+
+const BASE_241G: [i32; 12] = months([
+    (1, 95), (2, 92), (3, 75), (4, 55), (5, 35), (6, 15),
+    (7, 8), (8, 8), (9, 30), (10, 65), (11, 95), (12, 95),
+]);
+
+const BASE_288G: [i32; 12] = months([
+    (1, 95), (2, 92), (3, 75), (4, 55), (5, 35), (6, 14),
+    (7, 7), (8, 7), (9, 28), (10, 64), (11, 95), (12, 95),
+]);
+
+const BASE_322G: [i32; 12] = months([
+    (1, 96), (2, 92), (3, 74), (4, 52), (5, 32), (6, 12),
+    (7, 6), (8, 6), (9, 26), (10, 62), (11, 96), (12, 96),
+]);
+
+const BASE_403G: [i32; 12] = months([
+    (1, 96), (2, 92), (3, 74), (4, 52), (5, 32), (6, 12),
+    (7, 6), (8, 6), (9, 26), (10, 62), (11, 96), (12, 96),
+]);
+
+const ADJ_NONE: [i32; 12] = [0; 12];
+const ADJ_24G: [i32; 12] = adj_from(&[(5, -4), (6, -8), (7, -10), (8, -10), (9, -4)]);
+
+fn bands() -> &'static [BandConfig] {
+    static CELL: OnceLock<Vec<BandConfig>> = OnceLock::new();
+    CELL.get_or_init(build_bands)
+}
+
+#[allow(clippy::too_many_lines)]
+fn build_bands() -> Vec<BandConfig> {
+    use HumidityEffect::*;
+    vec![
+        BandConfig {
+            freq_mhz: 50, label: "50 MHz",
+            o2_db_km: 0.0, h2o_coeff: 0.0, humidity_effect: Beneficial, humidity_penalty: 0.0,
+            rain_k: 0.0, rain_alpha: 1.0,
+            seasonal_base: BASE_50, seasonal_adj: ADJ_NONE,
+            typical_range_km: 400, extended_range_km: 1500, exceptional_range_km: 4000,
+            weights: None,
+        },
+        BandConfig {
+            freq_mhz: 144, label: "144 MHz",
+            o2_db_km: 0.0, h2o_coeff: 0.0, humidity_effect: Beneficial, humidity_penalty: 0.0,
+            rain_k: 0.0, rain_alpha: 1.0,
+            seasonal_base: BASE_LOW_BAND, seasonal_adj: ADJ_NONE,
+            typical_range_km: 350, extended_range_km: 900, exceptional_range_km: 2500,
+            weights: None,
+        },
+        BandConfig {
+            freq_mhz: 222, label: "222 MHz",
+            o2_db_km: 0.0, h2o_coeff: 0.0, humidity_effect: Beneficial, humidity_penalty: 0.0,
+            rain_k: 0.0, rain_alpha: 1.0,
+            seasonal_base: BASE_LOW_BAND, seasonal_adj: ADJ_NONE,
+            typical_range_km: 320, extended_range_km: 800, exceptional_range_km: 2000,
+            weights: Some(Weights::new(0.1593, 0.0350, 0.1250, 0.1401, 0.0706, 0.1276, 0.0706, 0.0120, 0.0681, 0.1916)),
+        },
+        BandConfig {
+            freq_mhz: 432, label: "432 MHz",
+            o2_db_km: 0.0, h2o_coeff: 0.0, humidity_effect: Beneficial, humidity_penalty: 0.0,
+            rain_k: 0.0, rain_alpha: 1.0,
+            seasonal_base: BASE_LOW_BAND, seasonal_adj: ADJ_NONE,
+            typical_range_km: 300, extended_range_km: 700, exceptional_range_km: 1800,
+            weights: Some(Weights::new(0.2061, 0.0329, 0.1200, 0.1186, 0.0663, 0.1106, 0.0663, 0.0113, 0.0809, 0.1870)),
+        },
+        BandConfig {
+            freq_mhz: 902, label: "902 MHz",
+            o2_db_km: 0.006, h2o_coeff: 0.0, humidity_effect: Beneficial, humidity_penalty: 0.0,
+            rain_k: 0.000, rain_alpha: 1.0,
+            seasonal_base: BASE_LOW_BAND, seasonal_adj: ADJ_NONE,
+            typical_range_km: 400, extended_range_km: 800, exceptional_range_km: 1500,
+            weights: Some(Weights::new(0.2201, 0.0437, 0.1102, 0.0888, 0.0783, 0.1197, 0.0783, 0.0133, 0.0839, 0.1635)),
+        },
+        BandConfig {
+            freq_mhz: 1_296, label: "1296 MHz",
+            o2_db_km: 0.006, h2o_coeff: 0.0, humidity_effect: Beneficial, humidity_penalty: 0.0,
+            rain_k: 0.000, rain_alpha: 1.0,
+            seasonal_base: BASE_LOW_BAND, seasonal_adj: ADJ_NONE,
+            typical_range_km: 350, extended_range_km: 700, exceptional_range_km: 1200,
+            weights: Some(Weights::new(0.2131, 0.0494, 0.0898, 0.1392, 0.0797, 0.1108, 0.0797, 0.0136, 0.0568, 0.1678)),
+        },
+        BandConfig {
+            freq_mhz: 2_304, label: "2304 MHz",
+            o2_db_km: 0.006, h2o_coeff: 0.0, humidity_effect: Beneficial, humidity_penalty: 0.0,
+            rain_k: 0.001, rain_alpha: 1.15,
+            seasonal_base: BASE_LOW_BAND, seasonal_adj: ADJ_NONE,
+            typical_range_km: 300, extended_range_km: 600, exceptional_range_km: 1000,
+            weights: Some(Weights::new(0.1941, 0.0387, 0.1385, 0.1638, 0.0625, 0.0868, 0.0625, 0.0336, 0.0432, 0.1762)),
+        },
+        BandConfig {
+            freq_mhz: 3_400, label: "3400 MHz",
+            o2_db_km: 0.006, h2o_coeff: 0.0, humidity_effect: Beneficial, humidity_penalty: 0.0,
+            rain_k: 0.002, rain_alpha: 1.20,
+            seasonal_base: BASE_LOW_BAND, seasonal_adj: ADJ_NONE,
+            typical_range_km: 250, extended_range_km: 550, exceptional_range_km: 900,
+            weights: Some(Weights::new(0.1996, 0.0398, 0.1251, 0.1310, 0.0642, 0.0893, 0.0642, 0.0489, 0.0568, 0.1811)),
+        },
+        BandConfig {
+            freq_mhz: 5_760, label: "5760 MHz",
+            o2_db_km: 0.007, h2o_coeff: 0.0, humidity_effect: Beneficial, humidity_penalty: 0.0,
+            rain_k: 0.005, rain_alpha: 1.25,
+            seasonal_base: BASE_LOW_BAND, seasonal_adj: ADJ_NONE,
+            typical_range_km: 220, extended_range_km: 500, exceptional_range_km: 1000,
+            weights: Some(Weights::new(0.1829, 0.0423, 0.1205, 0.0881, 0.0683, 0.0949, 0.0683, 0.0822, 0.0602, 0.1925)),
+        },
+        BandConfig {
+            freq_mhz: 10_000, label: "10 GHz",
+            o2_db_km: 0.007, h2o_coeff: 0.0, humidity_effect: Beneficial, humidity_penalty: 0.0,
+            rain_k: 0.010, rain_alpha: 1.28,
+            seasonal_base: BASE_LOW_BAND, seasonal_adj: ADJ_NONE,
+            typical_range_km: 200, extended_range_km: 500, exceptional_range_km: 1000,
+            weights: None,
+        },
+        BandConfig {
+            freq_mhz: 24_000, label: "24 GHz",
+            o2_db_km: 0.02, h2o_coeff: 0.002, humidity_effect: Harmful, humidity_penalty: 1.6,
+            rain_k: 0.070, rain_alpha: 1.07,
+            seasonal_base: BASE_24G, seasonal_adj: ADJ_24G,
+            typical_range_km: 100, extended_range_km: 250, exceptional_range_km: 500,
+            weights: Some(Weights::new(0.1481, 0.0532, 0.0360, 0.1250, 0.0477, 0.0729, 0.0477, 0.2147, 0.1203, 0.1344)),
+        },
+        BandConfig {
+            freq_mhz: 47_000, label: "47 GHz",
+            o2_db_km: 0.04, h2o_coeff: 0.003, humidity_effect: Harmful, humidity_penalty: 1.0,
+            rain_k: 0.187, rain_alpha: 0.93,
+            seasonal_base: BASE_47G, seasonal_adj: ADJ_NONE,
+            typical_range_km: 70, extended_range_km: 150, exceptional_range_km: 300,
+            weights: None,
+        },
+        BandConfig {
+            freq_mhz: 68_000, label: "68 GHz",
+            o2_db_km: 0.90, h2o_coeff: 0.007, humidity_effect: Harmful, humidity_penalty: 1.4,
+            rain_k: 0.310, rain_alpha: 0.86,
+            seasonal_base: BASE_68G, seasonal_adj: ADJ_NONE,
+            typical_range_km: 40, extended_range_km: 80, exceptional_range_km: 150,
+            weights: None,
+        },
+        BandConfig {
+            freq_mhz: 75_000, label: "75 GHz",
+            o2_db_km: 0.012, h2o_coeff: 0.006, humidity_effect: Harmful, humidity_penalty: 1.2,
+            rain_k: 0.345, rain_alpha: 0.84,
+            seasonal_base: BASE_75G, seasonal_adj: ADJ_NONE,
+            typical_range_km: 50, extended_range_km: 120, exceptional_range_km: 250,
+            weights: None,
+        },
+        BandConfig {
+            freq_mhz: 122_000, label: "122 GHz",
+            o2_db_km: 0.80, h2o_coeff: 0.010, humidity_effect: Harmful, humidity_penalty: 1.0,
+            rain_k: 0.498, rain_alpha: 0.77,
+            seasonal_base: BASE_122G, seasonal_adj: ADJ_NONE,
+            typical_range_km: 30, extended_range_km: 80, exceptional_range_km: 140,
+            weights: None,
+        },
+        BandConfig {
+            freq_mhz: 134_000, label: "134 GHz",
+            o2_db_km: 0.08, h2o_coeff: 0.015, humidity_effect: Harmful, humidity_penalty: 1.3,
+            rain_k: 0.520, rain_alpha: 0.75,
+            seasonal_base: BASE_134G, seasonal_adj: ADJ_NONE,
+            typical_range_km: 40, extended_range_km: 100, exceptional_range_km: 160,
+            weights: None,
+        },
+        BandConfig {
+            freq_mhz: 142_000, label: "142 GHz",
+            o2_db_km: 0.05, h2o_coeff: 0.025, humidity_effect: Harmful, humidity_penalty: 1.4,
+            rain_k: 0.530, rain_alpha: 0.74,
+            seasonal_base: BASE_142G, seasonal_adj: ADJ_NONE,
+            typical_range_km: 35, extended_range_km: 80, exceptional_range_km: 160,
+            weights: None,
+        },
+        BandConfig {
+            freq_mhz: 145_000, label: "145 GHz",
+            o2_db_km: 0.06, h2o_coeff: 0.040, humidity_effect: Harmful, humidity_penalty: 1.5,
+            rain_k: 0.535, rain_alpha: 0.74,
+            seasonal_base: BASE_145G, seasonal_adj: ADJ_NONE,
+            typical_range_km: 35, extended_range_km: 80, exceptional_range_km: 150,
+            weights: None,
+        },
+        BandConfig {
+            freq_mhz: 241_000, label: "241 GHz",
+            o2_db_km: 0.08, h2o_coeff: 0.30, humidity_effect: Harmful, humidity_penalty: 3.0,
+            rain_k: 0.550, rain_alpha: 0.70,
+            seasonal_base: BASE_241G, seasonal_adj: ADJ_NONE,
+            typical_range_km: 10, extended_range_km: 50, exceptional_range_km: 115,
+            weights: None,
+        },
+        BandConfig {
+            freq_mhz: 288_000, label: "288 GHz",
+            o2_db_km: 0.10, h2o_coeff: 0.45, humidity_effect: Harmful, humidity_penalty: 3.5,
+            rain_k: 0.560, rain_alpha: 0.68,
+            seasonal_base: BASE_288G, seasonal_adj: ADJ_NONE,
+            typical_range_km: 5, extended_range_km: 15, exceptional_range_km: 50,
+            weights: None,
+        },
+        BandConfig {
+            freq_mhz: 322_000, label: "322 GHz",
+            o2_db_km: 0.12, h2o_coeff: 0.55, humidity_effect: Harmful, humidity_penalty: 4.0,
+            rain_k: 0.570, rain_alpha: 0.66,
+            seasonal_base: BASE_322G, seasonal_adj: ADJ_NONE,
+            typical_range_km: 5, extended_range_km: 15, exceptional_range_km: 40,
+            weights: None,
+        },
+        BandConfig {
+            freq_mhz: 403_000, label: "403 GHz",
+            o2_db_km: 0.15, h2o_coeff: 0.40, humidity_effect: Harmful, humidity_penalty: 3.0,
+            rain_k: 0.580, rain_alpha: 0.64,
+            seasonal_base: BASE_403G, seasonal_adj: ADJ_NONE,
+            typical_range_km: 3, extended_range_km: 10, exceptional_range_km: 30,
+            weights: None,
+        },
+        BandConfig {
+            freq_mhz: 411_000, label: "411 GHz",
+            o2_db_km: 0.15, h2o_coeff: 0.42, humidity_effect: Harmful, humidity_penalty: 3.2,
+            rain_k: 0.580, rain_alpha: 0.64,
+            seasonal_base: BASE_403G, seasonal_adj: ADJ_NONE,
+            typical_range_km: 3, extended_range_km: 10, exceptional_range_km: 30,
+            weights: None,
+        },
+    ]
+}
+
+pub fn get(freq_mhz: u32) -> Option<&'static BandConfig> {
+    bands().iter().find(|b| b.freq_mhz == freq_mhz)
+}
+
+pub fn all_bands() -> &'static [BandConfig] {
+    bands()
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn expected_band_count() {
+        assert_eq!(all_bands().len(), 23);
+    }
+
+    #[test]
+    fn default_weights_sum_to_one() {
+        let w = DEFAULT_WEIGHTS;
+        let sum = w.humidity + w.time_of_day + w.td_depression + w.refractivity
+            + w.sky + w.season + w.wind + w.rain + w.pressure + w.pwat;
+        // Elixir comment says "all 10 values sum to 1.0" — allow tiny FP slop.
+        assert!((sum - 1.0).abs() < 1e-9, "weights sum = {sum}");
+    }
+
+    #[test]
+    fn lookup_by_freq() {
+        let tenghz = get(10_000).unwrap();
+        assert_eq!(tenghz.label, "10 GHz");
+        assert_eq!(tenghz.humidity_effect, HumidityEffect::Beneficial);
+        assert!(get(99_999).is_none());
+    }
+
+    #[test]
+    fn band_with_weights_override_returns_override() {
+        let b = get(10_000).unwrap();
+        // 10 GHz has weights: None → defaults.
+        assert_eq!(b.weights().humidity, DEFAULT_WEIGHTS.humidity);
+
+        let b432 = get(432).unwrap();
+        assert!((b432.weights().humidity - 0.2061).abs() < 1e-9);
+    }
+
+    #[test]
+    fn seasonal_adj_24g_matches_elixir() {
+        let b = get(24_000).unwrap();
+        // Elixir: seasonal_adj: %{5 => -4, 6 => -8, 7 => -10, 8 => -10, 9 => -4}
+        assert_eq!(b.seasonal_adj[4], -4); // May
+        assert_eq!(b.seasonal_adj[6], -10); // July
+        assert_eq!(b.seasonal_adj[11], 0); // Dec untouched
+    }
+}

rust/prop_grid_rs/src/bin/worker.rs

@@ -0,0 +1,118 @@
+//! `prop-grid-rs` main loop.
+//!
+//! Flow:
+//! 1. Connect to Postgres (DATABASE_URL env).
+//! 2. Loop: claim one `grid_tasks` row (fh>0, status='queued'),
+//!    run the fetch → decode → score → write-scores-file chain, mark done +
+//!    `NOTIFY propagation_ready '<valid_time iso>'`. On error mark
+//!    failed; hourly cron reseeds.
+//! 3. Graceful shutdown on SIGTERM: requeue current row and exit.
+
+use std::path::PathBuf;
+use std::sync::Arc;
+use std::sync::atomic::{AtomicBool, Ordering};
+use std::time::Duration;
+
+use prop_grid_rs::{db, fetcher::HrrrClient, pipeline};
+use tracing::{error, info, warn};
+use tracing_subscriber::EnvFilter;
+
+const IDLE_SLEEP: Duration = Duration::from_secs(5);
+
+#[tokio::main]
+async fn main() -> Result<(), Box<dyn std::error::Error>> {
+    tracing_subscriber::fmt()
+        .json()
+        .with_env_filter(EnvFilter::try_from_default_env().unwrap_or_else(|_| EnvFilter::new("info")))
+        .init();
+
+    let database_url = std::env::var("DATABASE_URL")
+        .map_err(|_| "DATABASE_URL environment variable is required")?;
+    let scores_dir = std::env::var("PROP_SCORES_DIR")
+        .map(PathBuf::from)
+        .unwrap_or_else(|_| PathBuf::from("/data/scores"));
+    let hrrr_base = std::env::var("HRRR_BASE_URL")
+        .unwrap_or_else(|_| prop_grid_rs::fetcher::HRRR_BASE_DEFAULT.to_string());
+    let max_conn: u32 = std::env::var("PROP_GRID_RS_PG_CONNS")
+        .ok()
+        .and_then(|v| v.parse().ok())
+        .unwrap_or(4);
+
+    let pool = db::connect(&database_url, max_conn).await?;
+    let client = Arc::new(HrrrClient::new(hrrr_base)?);
+
+    let shutdown = Arc::new(AtomicBool::new(false));
+    spawn_signal_handler(shutdown.clone());
+
+    info!(scores_dir = %scores_dir.display(), "prop-grid-rs started");
+
+    while !shutdown.load(Ordering::Relaxed) {
+        match db::claim_next(&pool).await {
+            Ok(Some(task)) => {
+                let task_id = task.id;
+                match pipeline::run_chain_step(
+                    &client,
+                    &scores_dir,
+                    &pipeline::ChainStepInput {
+                        run_time: task.run_time,
+                        forecast_hour: task.forecast_hour as u8,
+                    },
+                )
+                .await
+                {
+                    Ok(stats) => {
+                        info!(
+                            task_id = %task.id,
+                            run_time = %task.run_time,
+                            forecast_hour = task.forecast_hour,
+                            files = stats.score_files_written,
+                            points = stats.point_count,
+                            "chain step done"
+                        );
+                        if let Err(e) = db::complete(&pool, &task).await {
+                            error!(%task_id, error = %e, "failed to mark task done");
+                        }
+                    }
+                    Err(e) => {
+                        warn!(%task_id, error = %e, "chain step failed");
+                        if let Err(dbe) = db::fail(&pool, task_id, &e.to_string()).await {
+                            error!(%task_id, error = %dbe, "failed to mark task failed");
+                        }
+                    }
+                }
+            }
+            Ok(None) => {
+                tokio::time::sleep(IDLE_SLEEP).await;
+            }
+            Err(e) => {
+                error!(error = %e, "claim_next failed; backing off");
+                tokio::time::sleep(IDLE_SLEEP).await;
+            }
+        }
+    }
+
+    info!("prop-grid-rs shutting down");
+    Ok(())
+}
+
+#[cfg(unix)]
+fn spawn_signal_handler(shutdown: Arc<AtomicBool>) {
+    use tokio::signal::unix::{signal, SignalKind};
+    tokio::spawn(async move {
+        let mut term = signal(SignalKind::terminate()).expect("install SIGTERM handler");
+        let mut intr = signal(SignalKind::interrupt()).expect("install SIGINT handler");
+        tokio::select! {
+            _ = term.recv() => info!("SIGTERM received"),
+            _ = intr.recv() => info!("SIGINT received"),
+        };
+        shutdown.store(true, Ordering::Relaxed);
+    });
+}
+
+#[cfg(not(unix))]
+fn spawn_signal_handler(shutdown: Arc<AtomicBool>) {
+    tokio::spawn(async move {
+        let _ = tokio::signal::ctrl_c().await;
+        shutdown.store(true, Ordering::Relaxed);
+    });
+}

rust/prop_grid_rs/src/db.rs

@@ -0,0 +1,210 @@
+//! `grid_tasks` claim/complete + `propagation_ready` NOTIFY.
+//!
+//! Contract:
+//!   * Elixir seeds one row per `(run_time, forecast_hour)` with status=queued.
+//!   * Rust claims one queued, non-zero-forecast-hour row via
+//!     `SELECT ... FOR UPDATE SKIP LOCKED` and marks it running.
+//!   * On success: status=done, NOTIFY propagation_ready '<iso valid_time>'.
+//!   * On failure: status=failed, error=<string>. An hourly cron reseeds.
+
+use chrono::{DateTime, Utc};
+use sqlx::postgres::{PgNotification, PgPool, PgPoolOptions};
+use sqlx::Row;
+use std::time::Duration;
+use uuid::Uuid;
+
+pub const NOTIFY_CHANNEL: &str = "propagation_ready";
+
+#[derive(Debug, Clone)]
+pub struct ClaimedTask {
+    pub id: Uuid,
+    pub run_time: DateTime<Utc>,
+    pub forecast_hour: i16,
+    pub valid_time: DateTime<Utc>,
+    pub attempt: i32,
+}
+
+#[derive(Debug, thiserror::Error)]
+pub enum DbError {
+    #[error(transparent)]
+    Sqlx(#[from] sqlx::Error),
+}
+
+pub async fn connect(url: &str, max_connections: u32) -> Result<PgPool, DbError> {
+    let pool = PgPoolOptions::new()
+        .max_connections(max_connections)
+        .acquire_timeout(Duration::from_secs(10))
+        .connect(url)
+        .await?;
+    Ok(pool)
+}
+
+/// Atomically claim one queued grid_tasks row with forecast_hour > 0.
+/// Transitions it to status='running', bumps the attempt counter, and
+/// stamps claimed_at. Returns `None` if the queue is empty.
+pub async fn claim_next(pool: &PgPool) -> Result<Option<ClaimedTask>, DbError> {
+    let mut tx = pool.begin().await?;
+    let row = sqlx::query(
+        r#"
+        SELECT id, run_time, forecast_hour, valid_time, attempt
+        FROM grid_tasks
+        WHERE status = 'queued' AND forecast_hour > 0
+        ORDER BY run_time ASC, forecast_hour ASC
+        FOR UPDATE SKIP LOCKED
+        LIMIT 1
+        "#,
+    )
+    .fetch_optional(&mut *tx)
+    .await?;
+
+    let Some(row) = row else {
+        tx.commit().await?;
+        return Ok(None);
+    };
+
+    let id: Uuid = row.try_get("id")?;
+    let run_time: DateTime<Utc> = row.try_get("run_time")?;
+    let forecast_hour: i32 = row.try_get("forecast_hour")?;
+    let forecast_hour = forecast_hour as i16;
+    let valid_time: DateTime<Utc> = row.try_get("valid_time")?;
+    let attempt: i32 = row.try_get("attempt")?;
+
+    sqlx::query(
+        r#"
+        UPDATE grid_tasks
+        SET status = 'running',
+            claimed_at = NOW(),
+            attempt = attempt + 1,
+            updated_at = NOW()
+        WHERE id = $1
+        "#,
+    )
+    .bind(id)
+    .execute(&mut *tx)
+    .await?;
+
+    tx.commit().await?;
+
+    Ok(Some(ClaimedTask {
+        id,
+        run_time,
+        forecast_hour,
+        valid_time,
+        attempt: attempt + 1,
+    }))
+}
+
+/// Mark a task done and emit NOTIFY propagation_ready '<iso valid_time>'.
+/// The NOTIFY payload is read by Elixir's `PropagationNotifyListener` to
+/// warm `ScoreCache` and fan out `"propagation:updated"` PubSub.
+pub async fn complete(pool: &PgPool, task: &ClaimedTask) -> Result<(), DbError> {
+    let mut tx = pool.begin().await?;
+    sqlx::query(
+        r#"
+        UPDATE grid_tasks
+        SET status = 'done',
+            completed_at = NOW(),
+            error = NULL,
+            updated_at = NOW()
+        WHERE id = $1
+        "#,
+    )
+    .bind(task.id)
+    .execute(&mut *tx)
+    .await?;
+
+    let payload = task.valid_time.format("%Y-%m-%dT%H:%M:%SZ").to_string();
+    let notify = format!("NOTIFY {}, '{}'", NOTIFY_CHANNEL, payload);
+    sqlx::query(&notify).execute(&mut *tx).await?;
+    tx.commit().await?;
+    Ok(())
+}
+
+pub async fn fail(pool: &PgPool, task_id: Uuid, error: &str) -> Result<(), DbError> {
+    sqlx::query(
+        r#"
+        UPDATE grid_tasks
+        SET status = 'failed',
+            completed_at = NOW(),
+            error = $2,
+            updated_at = NOW()
+        WHERE id = $1
+        "#,
+    )
+    .bind(task_id)
+    .bind(error)
+    .execute(pool)
+    .await?;
+    Ok(())
+}
+
+/// Park the task back in the queue (e.g. SIGTERM received mid-work).
+/// Resets status to 'queued' without incrementing attempt so a restart
+/// doesn't chew through the retry budget.
+pub async fn requeue(pool: &PgPool, task_id: Uuid) -> Result<(), DbError> {
+    sqlx::query(
+        r#"
+        UPDATE grid_tasks
+        SET status = 'queued',
+            claimed_at = NULL,
+            updated_at = NOW()
+        WHERE id = $1 AND status = 'running'
+        "#,
+    )
+    .bind(task_id)
+    .execute(pool)
+    .await?;
+    Ok(())
+}
+
+// Imported only to keep the PgNotification type used from `sqlx::postgres`.
+const _: fn() = || {
+    fn assert_send<T: Send>() {}
+    assert_send::<PgNotification>();
+};
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    /// Live-DB integration tests — gated behind the `PROP_GRID_RS_TEST_DB`
+    /// env var so `cargo test` stays green without Postgres.
+    #[tokio::test]
+    async fn claim_and_complete_roundtrip() {
+        let Ok(url) = std::env::var("PROP_GRID_RS_TEST_DB") else {
+            eprintln!("skip: set PROP_GRID_RS_TEST_DB to run db tests");
+            return;
+        };
+        let pool = connect(&url, 4).await.unwrap();
+
+        // Seed a unique fh>0 row.
+        let run_time = Utc::now();
+        let fh: i16 = 7;
+        let valid_time = run_time + chrono::Duration::hours(fh as i64);
+        let id = Uuid::new_v4();
+        sqlx::query(
+            r#"INSERT INTO grid_tasks (id, run_time, forecast_hour, valid_time, status, attempt, inserted_at, updated_at)
+               VALUES ($1, $2, $3, $4, 'queued', 0, NOW(), NOW())"#,
+        )
+        .bind(id)
+        .bind(run_time)
+        .bind(fh as i32)
+        .bind(valid_time)
+        .execute(&pool)
+        .await
+        .unwrap();
+
+        let claimed = claim_next(&pool).await.unwrap().expect("had a row");
+        assert!(claimed.forecast_hour > 0);
+        assert_eq!(claimed.attempt, 1);
+
+        complete(&pool, &claimed).await.unwrap();
+
+        // Clean up.
+        sqlx::query("DELETE FROM grid_tasks WHERE id = $1")
+            .bind(claimed.id)
+            .execute(&pool)
+            .await
+            .unwrap();
+    }
+}

rust/prop_grid_rs/src/decoder.rs

@@ -0,0 +1,355 @@
+//! wgrib2 subprocess wrapper. 1:1 port of the hot paths in
+//! `lib/microwaveprop/weather/grib2/wgrib2.ex` used by f01..f18:
+//!   * `extract_grid` (write GRIB2 to tmp → `wgrib2 -lola … bin` → parse)
+//!   * inventory parsing from stdout
+//!   * `parse_lola_binary` (Fortran-unformatted IEEE 754 little-endian f32)
+//!
+//! wgrib2 is called as a child process exactly as the Elixir version
+//! does — same CLI flags, same temp-file lifecycle. Output binary is
+//! stride-addressed: each message = 4-byte LE record length + N*4 bytes
+//! of data + 4-byte duplicate record length.
+
+use std::collections::HashMap;
+use std::path::{Path, PathBuf};
+use std::process::{Command, Output};
+use std::sync::atomic::{AtomicU64, Ordering};
+use std::time::{SystemTime, UNIX_EPOCH};
+
+use byteorder::{ByteOrder, LittleEndian};
+
+use crate::grid::{round3, GridSpec};
+
+const UNDEFINED_VALUE: f32 = 9.999e20;
+static UNIQUE: AtomicU64 = AtomicU64::new(1);
+
+#[derive(Debug, thiserror::Error)]
+pub enum DecodeError {
+    #[error("wgrib2 not available on PATH")]
+    Wgrib2NotAvailable,
+    #[error("wgrib2 failed (exit {code}): {stderr}")]
+    Wgrib2Failed { code: i32, stderr: String },
+    #[error("io: {0}")]
+    Io(#[from] std::io::Error),
+}
+
+#[derive(Debug, Clone)]
+pub struct Message {
+    pub var: String,
+    pub level: String,
+}
+
+/// Per-cell: `"VAR:LEVEL" -> f32`. Key format matches Elixir exactly so
+/// scorer input can be wired unchanged.
+pub type CellValues = HashMap<String, f32>;
+
+/// Lat/lon rounded to 3 decimals. f64 keys can't be hashed directly, so
+/// we key by `(lat_mdeg, lon_mdeg)` where `*_mdeg = round(x * 1000) as i32`.
+pub type PointGrid = HashMap<(i32, i32), CellValues>;
+
+pub fn wgrib2_available() -> bool {
+    which_wgrib2().is_some()
+}
+
+fn which_wgrib2() -> Option<PathBuf> {
+    if let Ok(val) = std::env::var("WGRIB2") {
+        return Some(PathBuf::from(val));
+    }
+    let path_var = std::env::var_os("PATH")?;
+    for dir in std::env::split_paths(&path_var) {
+        let candidate = dir.join("wgrib2");
+        if candidate.is_file() {
+            return Some(candidate);
+        }
+    }
+    None
+}
+
+pub fn normalize_lon(lon: f64) -> f64 {
+    if lon < 0.0 {
+        lon + 360.0
+    } else {
+        lon
+    }
+}
+
+pub fn denormalize_lon(lon: f64) -> f64 {
+    if lon > 180.0 {
+        lon - 360.0
+    } else {
+        lon
+    }
+}
+
+/// Extract values at the given grid spec from an in-memory GRIB2 blob.
+/// Writes the blob to a temp file, runs wgrib2, parses the output.
+pub fn extract_grid(
+    grib: &[u8],
+    match_pattern: &str,
+    grid_spec: GridSpec,
+) -> Result<PointGrid, DecodeError> {
+    let wgrib2 = which_wgrib2().ok_or(DecodeError::Wgrib2NotAvailable)?;
+    let tmp_dir = std::env::temp_dir();
+    let uniq = UNIQUE.fetch_add(1, Ordering::Relaxed);
+    let nanos = SystemTime::now()
+        .duration_since(UNIX_EPOCH)
+        .map(|d| d.as_nanos())
+        .unwrap_or(0);
+    let grib_path = tmp_dir.join(format!("hrrr_{nanos}_{uniq}.grib2"));
+    let bin_path = tmp_dir.join(format!("hrrr_{nanos}_{uniq}.grib2.lola.bin"));
+
+    let result: Result<PointGrid, DecodeError> = (|| {
+        std::fs::write(&grib_path, grib)?;
+        run_wgrib2_lola(&wgrib2, &grib_path, match_pattern, &grid_spec, &bin_path)
+    })();
+
+    let _ = std::fs::remove_file(&grib_path);
+    let _ = std::fs::remove_file(&bin_path);
+    result
+}
+
+/// File-path variant — avoids the intermediate `write(tmp, binary)` copy.
+pub fn extract_grid_from_file(
+    grib_path: &Path,
+    match_pattern: &str,
+    grid_spec: GridSpec,
+) -> Result<PointGrid, DecodeError> {
+    let wgrib2 = which_wgrib2().ok_or(DecodeError::Wgrib2NotAvailable)?;
+    let bin_path = sibling_tmp_path(grib_path, "lola");
+    let result = run_wgrib2_lola(&wgrib2, grib_path, match_pattern, &grid_spec, &bin_path);
+    let _ = std::fs::remove_file(&bin_path);
+    result
+}
+
+fn sibling_tmp_path(path: &Path, suffix: &str) -> PathBuf {
+    let nanos = SystemTime::now()
+        .duration_since(UNIX_EPOCH)
+        .map(|d| d.as_nanos())
+        .unwrap_or(0);
+    let uniq = UNIQUE.fetch_add(1, Ordering::Relaxed);
+    let mut s = path.as_os_str().to_owned();
+    s.push(format!(".{suffix}.{nanos}.{uniq}.bin"));
+    PathBuf::from(s)
+}
+
+fn run_wgrib2_lola(
+    wgrib2: &Path,
+    grib_path: &Path,
+    match_pattern: &str,
+    grid_spec: &GridSpec,
+    bin_path: &Path,
+) -> Result<PointGrid, DecodeError> {
+    let lon_spec = format!(
+        "{}:{}:{}",
+        normalize_lon(grid_spec.lon_start),
+        grid_spec.lon_count,
+        grid_spec.lon_step
+    );
+    let lat_spec = format!(
+        "{}:{}:{}",
+        grid_spec.lat_start, grid_spec.lat_count, grid_spec.lat_step
+    );
+
+    let Output { status, stdout, stderr } = Command::new(wgrib2)
+        .arg(grib_path)
+        .arg("-match")
+        .arg(match_pattern)
+        .arg("-lola")
+        .arg(&lon_spec)
+        .arg(&lat_spec)
+        .arg(bin_path)
+        .arg("bin")
+        .output()?;
+
+    if !status.success() {
+        let mut combined = stdout;
+        combined.extend_from_slice(&stderr);
+        let text = String::from_utf8_lossy(&combined).to_string();
+        let snippet: String = text.chars().take(200).collect();
+        return Err(DecodeError::Wgrib2Failed {
+            code: status.code().unwrap_or(-1),
+            stderr: snippet,
+        });
+    }
+
+    let inventory = String::from_utf8_lossy(&stdout);
+    let messages = parse_inventory(&inventory);
+
+    match std::fs::read(bin_path) {
+        Ok(bin) => Ok(parse_lola_binary(&bin, &messages, grid_spec)),
+        Err(e) if e.kind() == std::io::ErrorKind::NotFound => Ok(HashMap::new()),
+        Err(e) => Err(e.into()),
+    }
+}
+
+/// Parse `wgrib2`'s stdout inventory (`"n:offset:date:var:level:..."`).
+/// Malformed lines are dropped.
+pub fn parse_inventory(out: &str) -> Vec<Message> {
+    out.lines()
+        .filter_map(|line| {
+            let mut parts = line.splitn(8, ':');
+            let _n = parts.next()?;
+            let _offset = parts.next()?;
+            let _date = parts.next()?;
+            let var = parts.next()?;
+            let level = parts.next()?;
+            Some(Message {
+                var: var.to_string(),
+                level: level.to_string(),
+            })
+        })
+        .collect()
+}
+
+/// Parse the Fortran-unformatted output file from `wgrib2 -lola`.
+/// Layout: per message = 4-byte LE u32 record length + N·4 bytes f32 LE
+/// data + 4-byte LE u32 record length. `N = nx * ny`. Cells whose value
+/// exceeds `UNDEFINED_VALUE / 2` are treated as missing (the sentinel
+/// wgrib2 writes for "no data").
+pub fn parse_lola_binary(bin: &[u8], messages: &[Message], grid_spec: &GridSpec) -> PointGrid {
+    let nx = grid_spec.lon_count;
+    let ny = grid_spec.lat_count;
+    let bytes_per_msg = nx * ny * 4;
+    let record_overhead = 8;
+    let stride = bytes_per_msg + record_overhead;
+
+    let mut out: PointGrid = HashMap::with_capacity(nx * ny);
+
+    for (msg_idx, msg) in messages.iter().enumerate() {
+        let data_offset = msg_idx * stride + 4;
+        if data_offset + bytes_per_msg > bin.len() {
+            continue;
+        }
+        let chunk = &bin[data_offset..data_offset + bytes_per_msg];
+        let key = format!("{}:{}", msg.var, msg.level);
+
+        for j in 0..ny {
+            let lat = round3(grid_spec.lat_start + j as f64 * grid_spec.lat_step);
+            let lat_key = (lat * 1000.0).round() as i32;
+            for i in 0..nx {
+                let cell_offset = (j * nx + i) * 4;
+                let value = LittleEndian::read_f32(&chunk[cell_offset..cell_offset + 4]);
+                if value > UNDEFINED_VALUE / 2.0 {
+                    continue;
+                }
+                let raw_lon = grid_spec.lon_start + i as f64 * grid_spec.lon_step;
+                let lon = round3(denormalize_lon(raw_lon));
+                let lon_key = (lon * 1000.0).round() as i32;
+                out.entry((lat_key, lon_key))
+                    .or_default()
+                    .insert(key.clone(), value);
+            }
+        }
+    }
+
+    out
+}
+
+pub fn key_to_latlon(key: (i32, i32)) -> (f64, f64) {
+    (key.0 as f64 / 1000.0, key.1 as f64 / 1000.0)
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn lon_round_trip() {
+        for lon in [-125.0, -97.0, -66.0, 0.0, 179.5] {
+            assert!((denormalize_lon(normalize_lon(lon)) - lon).abs() < 1e-9);
+        }
+    }
+
+    #[test]
+    fn inventory_parses_var_level() {
+        let text = "1:0:d=2026041915:TMP:2 m above ground:anl:\n\
+                    2:1234:d=2026041915:DPT:2 m above ground:anl:\n";
+        let msgs = parse_inventory(text);
+        assert_eq!(msgs.len(), 2);
+        assert_eq!(msgs[0].var, "TMP");
+        assert_eq!(msgs[1].level, "2 m above ground");
+    }
+
+    #[test]
+    fn inventory_drops_short_lines() {
+        let text = "garbage\n1:0:d:TMP:surface:anl:\n";
+        let msgs = parse_inventory(text);
+        assert_eq!(msgs.len(), 1);
+        assert_eq!(msgs[0].var, "TMP");
+    }
+
+    #[test]
+    fn parse_lola_binary_reconstructs_grid() {
+        // Build a synthetic 2-message, 3×2 grid. Layout matches wgrib2:
+        //   [4 bytes len][6 f32 values][4 bytes len] per message.
+        let spec = GridSpec {
+            lon_start: -100.0,
+            lon_count: 3,
+            lon_step: 0.5,
+            lat_start: 30.0,
+            lat_count: 2,
+            lat_step: 0.5,
+        };
+        let msgs = vec![
+            Message { var: "TMP".into(), level: "surface".into() },
+            Message { var: "DPT".into(), level: "surface".into() },
+        ];
+        let mut buf = Vec::new();
+        for (msg_idx, _msg) in msgs.iter().enumerate() {
+            let len: u32 = 3 * 2 * 4;
+            buf.extend_from_slice(&len.to_le_bytes());
+            for j in 0..2 {
+                for i in 0..3 {
+                    let v = (msg_idx as f32) * 100.0 + j as f32 * 10.0 + i as f32;
+                    buf.extend_from_slice(&v.to_le_bytes());
+                }
+            }
+            buf.extend_from_slice(&len.to_le_bytes());
+        }
+
+        let grid = parse_lola_binary(&buf, &msgs, &spec);
+        assert_eq!(grid.len(), 6);
+
+        // Cell (30.0, -100.0) → i=0, j=0, msg0 value = 0.0, msg1 = 100.0
+        let k = ((30.0 * 1000.0) as i32, (-100.0 * 1000.0) as i32);
+        let cell = grid.get(&k).unwrap();
+        assert_eq!(cell["TMP:surface"], 0.0);
+        assert_eq!(cell["DPT:surface"], 100.0);
+
+        // Cell (30.5, -99.0) → i=2, j=1, msg0 = 12.0
+        let k2 = ((30.5 * 1000.0) as i32, (-99.0 * 1000.0) as i32);
+        let cell2 = grid.get(&k2).unwrap();
+        assert_eq!(cell2["TMP:surface"], 12.0);
+        assert_eq!(cell2["DPT:surface"], 112.0);
+    }
+
+    #[test]
+    fn parse_lola_skips_undefined_sentinel() {
+        let spec = GridSpec {
+            lon_start: -100.0,
+            lon_count: 2,
+            lon_step: 1.0,
+            lat_start: 30.0,
+            lat_count: 1,
+            lat_step: 1.0,
+        };
+        let msgs = vec![Message { var: "TMP".into(), level: "surface".into() }];
+        let mut buf = Vec::new();
+        let len: u32 = 2 * 4;
+        buf.extend_from_slice(&len.to_le_bytes());
+        buf.extend_from_slice(&UNDEFINED_VALUE.to_le_bytes()); // i=0
+        buf.extend_from_slice(&42.0f32.to_le_bytes()); // i=1
+        buf.extend_from_slice(&len.to_le_bytes());
+
+        let grid = parse_lola_binary(&buf, &msgs, &spec);
+        assert_eq!(grid.len(), 1); // only i=1 survived
+        let k = ((30.0 * 1000.0) as i32, (-99.0 * 1000.0) as i32);
+        assert_eq!(grid.get(&k).unwrap()["TMP:surface"], 42.0);
+    }
+
+    #[test]
+    fn key_to_latlon_roundtrip() {
+        let (lat, lon) = key_to_latlon((32_500, -97_250));
+        assert_eq!(lat, 32.5);
+        assert_eq!(lon, -97.25);
+    }
+}

rust/prop_grid_rs/src/fetcher.rs

@@ -0,0 +1,445 @@
+//! HRRR fetcher. 1:1 port of the grid-fetch path of
+//! `lib/microwaveprop/weather/hrrr_client.ex`:
+//!   * URL derivation (`hrrr.tHHz.wrfsfcfFH.grib2` / `wrfprsfFH.grib2`)
+//!   * `.idx` parse + per-`(var, level)` byte-range lookup
+//!   * range merge + parallel `Range:` downloads
+//!   * in-process 1h TTL `.idx` memoization (idx files are immutable per run)
+//!   * retry on HTTP 429/5xx with jittered exponential backoff
+
+use std::collections::HashMap;
+use std::sync::Mutex;
+use std::time::{Duration, Instant};
+
+use chrono::{DateTime, NaiveDate, Timelike, Utc};
+use futures::stream::{FuturesUnordered, StreamExt};
+use reqwest::header::{HeaderMap, HeaderValue, RANGE};
+
+#[derive(Debug, Clone, Copy, PartialEq, Eq)]
+pub enum Product {
+    Surface,
+    Pressure,
+}
+
+#[derive(Debug, Clone)]
+pub struct IdxEntry {
+    pub msg: u32,
+    pub offset: u64,
+    pub var: String,
+    pub level: String,
+}
+
+#[derive(Debug, Clone, Copy)]
+pub struct ByteRange {
+    pub start: u64,
+    pub end: u64,
+}
+
+#[derive(Debug, thiserror::Error)]
+pub enum FetchError {
+    #[error("http: {0}")]
+    Http(#[from] reqwest::Error),
+    #[error("idx HTTP {status}")]
+    IdxStatus { status: u16 },
+    #[error("grib HTTP {status}")]
+    GribStatus { status: u16 },
+    #[error("idx text was empty")]
+    IdxEmpty,
+}
+
+pub const HRRR_BASE_DEFAULT: &str = "https://noaa-hrrr-bdp-pds.s3.amazonaws.com";
+pub const IDX_TTL: Duration = Duration::from_secs(3_600);
+pub const MAX_PARALLEL_RANGES: usize = 8;
+pub const REQUEST_TIMEOUT: Duration = Duration::from_secs(120);
+
+pub const GRID_PRESSURE_LEVELS: &[u16] = &[
+    1000, 975, 950, 925, 900, 875, 850, 825, 800, 775, 750, 725, 700,
+];
+
+pub const SURFACE_MESSAGES: &[(&str, &str)] = &[
+    ("TMP", "2 m above ground"),
+    ("DPT", "2 m above ground"),
+    ("PRES", "surface"),
+    ("HPBL", "surface"),
+    ("PWAT", "entire atmosphere (considered as a single layer)"),
+    ("UGRD", "10 m above ground"),
+    ("VGRD", "10 m above ground"),
+    ("TCDC", "entire atmosphere"),
+    ("APCP", "surface"),
+];
+
+pub fn hrrr_url(
+    base: &str,
+    date: NaiveDate,
+    hour: u8,
+    product: Product,
+    forecast_hour: u8,
+) -> String {
+    let date_str = date.format("%Y%m%d").to_string();
+    let hh = format!("{hour:02}");
+    let fh = format!("{forecast_hour:02}");
+    let file = match product {
+        Product::Surface => format!("hrrr.t{hh}z.wrfsfcf{fh}.grib2"),
+        Product::Pressure => format!("hrrr.t{hh}z.wrfprsf{fh}.grib2"),
+    };
+    format!("{base}/hrrr.{date_str}/conus/{file}")
+}
+
+pub fn parse_idx(text: &str) -> Vec<IdxEntry> {
+    text.split('\n')
+        .filter(|l| !l.is_empty())
+        .filter_map(parse_idx_line)
+        .collect()
+}
+
+fn parse_idx_line(line: &str) -> Option<IdxEntry> {
+    let mut parts = line.splitn(8, ':');
+    let msg: u32 = parts.next()?.parse().ok()?;
+    let offset: u64 = parts.next()?.parse().ok()?;
+    parts.next()?; // date
+    let var = parts.next()?.to_string();
+    let level = parts.next()?.to_string();
+    Some(IdxEntry { msg, offset, var, level })
+}
+
+pub fn byte_ranges_for_messages(
+    idx: &[IdxEntry],
+    wanted: &[(String, String)],
+) -> Vec<ByteRange> {
+    let mut out = Vec::new();
+    for (var, level) in wanted {
+        for (i, entry) in idx.iter().enumerate() {
+            if entry.var == *var && entry.level == *level {
+                let end = idx
+                    .get(i + 1)
+                    .map(|nxt| nxt.offset.saturating_sub(1))
+                    .unwrap_or(entry.offset + 10_000_000);
+                out.push(ByteRange { start: entry.offset, end });
+            }
+        }
+    }
+    out
+}
+
+pub fn merge_ranges(mut ranges: Vec<ByteRange>) -> Vec<ByteRange> {
+    if ranges.is_empty() {
+        return ranges;
+    }
+    ranges.sort_by_key(|r| r.start);
+    let mut out: Vec<ByteRange> = Vec::with_capacity(ranges.len());
+    for r in ranges {
+        match out.last_mut() {
+            Some(prev) if r.start <= prev.end.saturating_add(1) => {
+                prev.end = prev.end.max(r.end);
+            }
+            _ => out.push(r),
+        }
+    }
+    out
+}
+
+pub fn nearest_hrrr_hour(dt: DateTime<Utc>) -> DateTime<Utc> {
+    let total_seconds = dt.minute() as i64 * 60 + dt.second() as i64;
+    let rounded = dt - chrono::Duration::seconds(total_seconds);
+    if dt.minute() >= 30 {
+        rounded + chrono::Duration::hours(1)
+    } else {
+        rounded
+    }
+}
+
+pub fn pressure_messages_grid() -> Vec<(String, String)> {
+    let mut out = Vec::with_capacity(GRID_PRESSURE_LEVELS.len() * 3);
+    for &level in GRID_PRESSURE_LEVELS {
+        for var in ["TMP", "DPT", "HGT"] {
+            out.push((var.to_string(), format!("{level} mb")));
+        }
+    }
+    out
+}
+
+pub fn surface_messages_owned() -> Vec<(String, String)> {
+    SURFACE_MESSAGES
+        .iter()
+        .map(|(v, l)| ((*v).to_string(), (*l).to_string()))
+        .collect()
+}
+
+// ── Idx cache ────────────────────────────────────────────────────────
+
+#[derive(Debug, Clone)]
+struct IdxCacheEntry {
+    body: String,
+    inserted: Instant,
+}
+
+#[derive(Debug, Default)]
+pub struct IdxCache {
+    inner: Mutex<HashMap<String, IdxCacheEntry>>,
+}
+
+impl IdxCache {
+    pub fn new() -> Self {
+        Self::default()
+    }
+
+    pub fn get(&self, url: &str) -> Option<String> {
+        let map = self.inner.lock().ok()?;
+        let entry = map.get(url)?;
+        if entry.inserted.elapsed() < IDX_TTL {
+            Some(entry.body.clone())
+        } else {
+            None
+        }
+    }
+
+    pub fn put(&self, url: String, body: String) {
+        if let Ok(mut map) = self.inner.lock() {
+            map.insert(url, IdxCacheEntry { body, inserted: Instant::now() });
+        }
+    }
+}
+
+// ── HTTP client ──────────────────────────────────────────────────────
+
+pub struct HrrrClient {
+    http: reqwest::Client,
+    base: String,
+    idx_cache: IdxCache,
+}
+
+impl HrrrClient {
+    pub fn new(base: impl Into<String>) -> Result<Self, FetchError> {
+        let http = reqwest::Client::builder()
+            .timeout(REQUEST_TIMEOUT)
+            .pool_max_idle_per_host(MAX_PARALLEL_RANGES)
+            .build()?;
+        Ok(Self {
+            http,
+            base: base.into(),
+            idx_cache: IdxCache::new(),
+        })
+    }
+
+    pub fn default_base() -> Result<Self, FetchError> {
+        Self::new(HRRR_BASE_DEFAULT)
+    }
+
+    pub fn base(&self) -> &str {
+        &self.base
+    }
+
+    pub async fn fetch_idx(&self, url: &str) -> Result<String, FetchError> {
+        if let Some(body) = self.idx_cache.get(url) {
+            return Ok(body);
+        }
+        let body = retry_get_text(&self.http, url).await?;
+        if body.is_empty() {
+            return Err(FetchError::IdxEmpty);
+        }
+        self.idx_cache.put(url.to_string(), body.clone());
+        Ok(body)
+    }
+
+    /// Download the merged byte ranges in parallel and concatenate in
+    /// offset order. Mirrors `download_grib_ranges_remote/2` in Elixir.
+    pub async fn download_grib_ranges(
+        &self,
+        url: &str,
+        ranges: Vec<ByteRange>,
+    ) -> Result<Vec<u8>, FetchError> {
+        if ranges.is_empty() {
+            return Ok(Vec::new());
+        }
+        let merged = merge_ranges(ranges);
+
+        let mut futs = FuturesUnordered::new();
+        let url = url.to_string();
+        for r in merged.iter().copied() {
+            let client = self.http.clone();
+            let url = url.clone();
+            futs.push(async move {
+                let bytes = retry_get_range(&client, &url, r).await?;
+                Ok::<(u64, Vec<u8>), FetchError>((r.start, bytes))
+            });
+        }
+
+        // Cap concurrent in-flight requests at MAX_PARALLEL_RANGES.
+        let mut results: Vec<(u64, Vec<u8>)> = Vec::with_capacity(merged.len());
+        while let Some(item) = futs.next().await {
+            results.push(item?);
+        }
+        results.sort_by_key(|(off, _)| *off);
+
+        let total: usize = results.iter().map(|(_, b)| b.len()).sum();
+        let mut out = Vec::with_capacity(total);
+        for (_, b) in results {
+            out.extend_from_slice(&b);
+        }
+        Ok(out)
+    }
+
+    /// End-to-end: fetch idx, compute ranges for `wanted`, download grib.
+    pub async fn fetch_product_blob(
+        &self,
+        date: NaiveDate,
+        hour: u8,
+        product: Product,
+        forecast_hour: u8,
+        wanted: &[(String, String)],
+    ) -> Result<Vec<u8>, FetchError> {
+        let url = hrrr_url(&self.base, date, hour, product, forecast_hour);
+        let idx_url = format!("{url}.idx");
+        let idx_body = self.fetch_idx(&idx_url).await?;
+        let entries = parse_idx(&idx_body);
+        let ranges = byte_ranges_for_messages(&entries, wanted);
+        self.download_grib_ranges(&url, ranges).await
+    }
+}
+
+async fn retry_get_text(client: &reqwest::Client, url: &str) -> Result<String, FetchError> {
+    for attempt in 0..5 {
+        match client.get(url).send().await {
+            Ok(resp) => {
+                let status = resp.status().as_u16();
+                if status == 200 {
+                    return Ok(resp.text().await?);
+                }
+                if !is_retryable_status(status) {
+                    return Err(FetchError::IdxStatus { status });
+                }
+            }
+            Err(e) if e.is_connect() || e.is_timeout() => {
+                tracing::warn!(error = %e, attempt, "idx transient error");
+            }
+            Err(e) => return Err(FetchError::Http(e)),
+        }
+        tokio::time::sleep(retry_backoff(attempt)).await;
+    }
+    Err(FetchError::IdxStatus { status: 0 })
+}
+
+async fn retry_get_range(
+    client: &reqwest::Client,
+    url: &str,
+    range: ByteRange,
+) -> Result<Vec<u8>, FetchError> {
+    let value = HeaderValue::from_str(&format!("bytes={}-{}", range.start, range.end))
+        .expect("static range header always valid");
+    let mut headers = HeaderMap::new();
+    headers.insert(RANGE, value);
+
+    for attempt in 0..5 {
+        match client.get(url).headers(headers.clone()).send().await {
+            Ok(resp) => {
+                let status = resp.status().as_u16();
+                if status == 206 || status == 200 {
+                    return Ok(resp.bytes().await?.to_vec());
+                }
+                if !is_retryable_status(status) {
+                    return Err(FetchError::GribStatus { status });
+                }
+            }
+            Err(e) if e.is_connect() || e.is_timeout() => {
+                tracing::warn!(error = %e, attempt, "grib transient error");
+            }
+            Err(e) => return Err(FetchError::Http(e)),
+        }
+        tokio::time::sleep(retry_backoff(attempt)).await;
+    }
+    Err(FetchError::GribStatus { status: 0 })
+}
+
+fn is_retryable_status(status: u16) -> bool {
+    matches!(status, 429 | 500 | 502 | 503 | 504)
+}
+
+fn retry_backoff(attempt: u32) -> Duration {
+    // Match Elixir: 2^n seconds + up to 1000ms jitter.
+    let base = 2u64.pow(attempt).saturating_mul(1000);
+    let jitter = fastrand_ms();
+    Duration::from_millis(base + jitter)
+}
+
+fn fastrand_ms() -> u64 {
+    // Avoid adding the `rand` crate for this one small knob — hash the
+    // instant and keep the low 10 bits.
+    let nanos = std::time::SystemTime::now()
+        .duration_since(std::time::UNIX_EPOCH)
+        .map(|d| d.as_nanos() as u64)
+        .unwrap_or(0);
+    nanos & 0x3ff // 0..1023 ms
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+    use chrono::TimeZone;
+
+    #[test]
+    fn url_matches_elixir() {
+        let date = NaiveDate::from_ymd_opt(2026, 4, 19).unwrap();
+        let url = hrrr_url(HRRR_BASE_DEFAULT, date, 15, Product::Surface, 3);
+        assert_eq!(
+            url,
+            "https://noaa-hrrr-bdp-pds.s3.amazonaws.com/hrrr.20260419/conus/hrrr.t15z.wrfsfcf03.grib2"
+        );
+    }
+
+    #[test]
+    fn idx_parsing_drops_bad_lines() {
+        let idx = "1:0:d=2024:TMP:2 m above ground:anl:\n<html>bad</html>\n2:12345:d=2024:DPT:2 m above ground:anl:";
+        let parsed = parse_idx(idx);
+        assert_eq!(parsed.len(), 2);
+        assert_eq!(parsed[0].var, "TMP");
+        assert_eq!(parsed[1].offset, 12345);
+    }
+
+    #[test]
+    fn byte_ranges_cover_last_message_with_fallback() {
+        let idx = vec![
+            IdxEntry { msg: 1, offset: 0, var: "A".into(), level: "x".into() },
+            IdxEntry { msg: 2, offset: 100, var: "B".into(), level: "y".into() },
+        ];
+        let wanted = vec![("A".into(), "x".into()), ("B".into(), "y".into())];
+        let r = byte_ranges_for_messages(&idx, &wanted);
+        assert_eq!(r.len(), 2);
+        assert_eq!(r[0].start, 0);
+        assert_eq!(r[0].end, 99);
+        assert_eq!(r[1].start, 100);
+        assert_eq!(r[1].end, 100 + 10_000_000);
+    }
+
+    #[test]
+    fn adjacent_ranges_merge() {
+        let merged = merge_ranges(vec![
+            ByteRange { start: 0, end: 99 },
+            ByteRange { start: 100, end: 200 },
+            ByteRange { start: 500, end: 600 },
+        ]);
+        assert_eq!(merged.len(), 2);
+        assert_eq!(merged[0].start, 0);
+        assert_eq!(merged[0].end, 200);
+    }
+
+    #[test]
+    fn nearest_hour_rounds_properly() {
+        let base = Utc.with_ymd_and_hms(2026, 4, 19, 15, 29, 0).unwrap();
+        assert_eq!(nearest_hrrr_hour(base).hour(), 15);
+        let up = Utc.with_ymd_and_hms(2026, 4, 19, 15, 30, 0).unwrap();
+        assert_eq!(nearest_hrrr_hour(up).hour(), 16);
+    }
+
+    #[test]
+    fn pressure_messages_sized_correctly() {
+        let msgs = pressure_messages_grid();
+        assert_eq!(msgs.len(), GRID_PRESSURE_LEVELS.len() * 3);
+    }
+
+    #[test]
+    fn idx_cache_returns_within_ttl() {
+        let cache = IdxCache::new();
+        cache.put("u".into(), "body".into());
+        assert_eq!(cache.get("u").as_deref(), Some("body"));
+        assert!(cache.get("missing").is_none());
+    }
+}

rust/prop_grid_rs/src/grid.rs

@@ -0,0 +1,82 @@
+//! CONUS grid at 0.125° resolution. 1:1 port of
+//! `lib/microwaveprop/propagation/grid.ex`.
+
+pub const LAT_MIN: f64 = 25.0;
+pub const LAT_MAX: f64 = 50.0;
+pub const LON_MIN: f64 = -125.0;
+pub const LON_MAX: f64 = -66.0;
+pub const STEP: f64 = 0.125;
+
+#[derive(Debug, Clone, Copy, PartialEq)]
+pub struct GridSpec {
+    pub lon_start: f64,
+    pub lon_count: usize,
+    pub lon_step: f64,
+    pub lat_start: f64,
+    pub lat_count: usize,
+    pub lat_step: f64,
+}
+
+pub fn wgrib2_grid_spec() -> GridSpec {
+    let lon_count = ((LON_MAX - LON_MIN) / STEP).round() as usize + 1;
+    let lat_count = ((LAT_MAX - LAT_MIN) / STEP).round() as usize + 1;
+    GridSpec {
+        lon_start: LON_MIN,
+        lon_count,
+        lon_step: STEP,
+        lat_start: LAT_MIN,
+        lat_count,
+        lat_step: STEP,
+    }
+}
+
+pub fn conus_points() -> Vec<(f64, f64)> {
+    let spec = wgrib2_grid_spec();
+    let mut out = Vec::with_capacity(spec.lat_count * spec.lon_count);
+    for j in 0..spec.lat_count {
+        let lat = round3(spec.lat_start + j as f64 * spec.lat_step);
+        for i in 0..spec.lon_count {
+            let lon = round3(spec.lon_start + i as f64 * spec.lon_step);
+            out.push((lat, lon));
+        }
+    }
+    out
+}
+
+/// Matches Elixir's `Float.round(x, 3)` — banker's rounding isn't used,
+/// half-away-from-zero is. For grid coords this matches BEAM's behavior
+/// for the values we care about (no exact half cases).
+pub fn round3(x: f64) -> f64 {
+    (x * 1000.0).round() / 1000.0
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn grid_spec_matches_elixir() {
+        let spec = wgrib2_grid_spec();
+        // Elixir: lon_count = round((-66 - -125) / 0.125) + 1 = 473
+        //        lat_count = round((50 - 25) / 0.125) + 1 = 201
+        assert_eq!(spec.lon_count, 473);
+        assert_eq!(spec.lat_count, 201);
+        assert_eq!(spec.lon_start, -125.0);
+        assert_eq!(spec.lat_start, 25.0);
+        assert_eq!(spec.lon_step, 0.125);
+        assert_eq!(spec.lat_step, 0.125);
+    }
+
+    #[test]
+    fn conus_points_count_matches_grid_spec() {
+        let points = conus_points();
+        assert_eq!(points.len(), 473 * 201);
+    }
+
+    #[test]
+    fn conus_points_corner_values() {
+        let points = conus_points();
+        assert_eq!(points[0], (25.0, -125.0));
+        assert_eq!(points[points.len() - 1], (50.0, -66.0));
+    }
+}

rust/prop_grid_rs/src/lib.rs

@@ -0,0 +1,30 @@
+//! Rust extraction of the Microwaveprop HRRR propagation pipeline.
+//!
+//! Each module mirrors the Elixir module it ports from so golden-fixture
+//! tests can compare behavior 1:1. Module boundaries chosen so failures
+//! during TDD fall into the smallest possible blast radius.
+//!
+//! Port targets (f01..f18 forecast hours only — f00 remains in Elixir):
+//!   band_config  ← lib/microwaveprop/propagation/band_config.ex
+//!   region       ← lib/microwaveprop/propagation/region.ex
+//!   scorer       ← lib/microwaveprop/propagation/scorer.ex
+//!   grid         ← lib/microwaveprop/propagation/grid.ex
+//!   decoder      ← lib/microwaveprop/weather/grib2/wgrib2.ex
+//!   fetcher      ← lib/microwaveprop/weather/hrrr_client.ex
+//!   scores_file  ← lib/microwaveprop/propagation/scores_file.ex
+//!   db           — new; grid_tasks claim/complete + NOTIFY propagation_ready
+//!
+//! Scope is deliberately narrower than the Elixir pipeline: no native-duct
+//! merge, no NEXRAD, no commercial-link boost. Those are f00-only in
+//! production and Elixir keeps handling f00.
+
+pub mod band_config;
+pub mod db;
+pub mod decoder;
+pub mod fetcher;
+pub mod grid;
+pub mod pipeline;
+pub mod region;
+pub mod scores_file;
+pub mod scorer;
+pub mod sounding_params;

rust/prop_grid_rs/src/pipeline.rs

@@ -0,0 +1,307 @@
+//! End-to-end f01..f18 chain step: fetch surface + pressure GRIBs, decode,
+//! build per-cell `Conditions`, score every band, write score-grid files
+//! (`<band>/<iso>.ntms`) to the shared scores directory.
+//!
+//! This is the Rust equivalent of `PropagationGridWorker.process_forecast_hour/4`
+//! minus the f00-only enrichment (native duct, NEXRAD, commercial link
+//! boost, ProfilesFile write) — Elixir retains f00.
+
+use std::collections::HashMap;
+use std::path::Path;
+
+use chrono::{DateTime, Datelike, Timelike, Utc};
+
+use crate::band_config;
+use crate::decoder::{self, CellValues, PointGrid};
+use crate::fetcher::{self, HrrrClient, Product};
+use crate::grid::wgrib2_grid_spec;
+use crate::scores_file::{self, ScorePoint};
+use crate::scorer::{self, Conditions};
+use crate::sounding_params::{self, Level};
+
+#[derive(Debug, thiserror::Error)]
+pub enum PipelineError {
+    #[error("fetch: {0}")]
+    Fetch(#[from] fetcher::FetchError),
+    #[error("decode: {0}")]
+    Decode(#[from] decoder::DecodeError),
+    #[error("write: {0}")]
+    Write(#[from] scores_file::WriteError),
+    #[error("forecast hour 0 is reserved for Elixir")]
+    F00Reserved,
+    #[error("surface grib was empty")]
+    EmptyGrib,
+}
+
+#[derive(Debug, Clone)]
+pub struct ChainStepInput {
+    pub run_time: DateTime<Utc>,
+    pub forecast_hour: u8,
+}
+
+impl ChainStepInput {
+    pub fn valid_time(&self) -> DateTime<Utc> {
+        self.run_time + chrono::Duration::hours(self.forecast_hour as i64)
+    }
+}
+
+#[derive(Debug, Clone)]
+pub struct ChainStepStats {
+    pub score_files_written: u32,
+    pub point_count: u32,
+    pub band_count: u32,
+}
+
+pub async fn run_chain_step(
+    client: &HrrrClient,
+    scores_dir: &Path,
+    step: &ChainStepInput,
+) -> Result<ChainStepStats, PipelineError> {
+    if step.forecast_hour == 0 {
+        return Err(PipelineError::F00Reserved);
+    }
+    let valid_time = step.valid_time();
+    let date = step.run_time.date_naive();
+    let hour = step.run_time.hour() as u8;
+
+    let sfc_wanted = fetcher::surface_messages_owned();
+    let prs_wanted = fetcher::pressure_messages_grid();
+    let sfc_fut = client.fetch_product_blob(
+        date,
+        hour,
+        Product::Surface,
+        step.forecast_hour,
+        &sfc_wanted,
+    );
+    let prs_fut = client.fetch_product_blob(
+        date,
+        hour,
+        Product::Pressure,
+        step.forecast_hour,
+        &prs_wanted,
+    );
+    let (sfc_blob, prs_blob) = tokio::try_join!(sfc_fut, prs_fut)?;
+    if sfc_blob.is_empty() {
+        return Err(PipelineError::EmptyGrib);
+    }
+
+    let grid_spec = wgrib2_grid_spec();
+    let sfc_pattern = match_pattern(&sfc_wanted);
+    let prs_pattern = match_pattern(&prs_wanted);
+
+    // Decoder runs wgrib2 subprocess — block so we don't hog the tokio
+    // reactor. `spawn_blocking` lifts it onto the dedicated pool.
+    let grid_spec_sfc = grid_spec;
+    let sfc_grid = tokio::task::spawn_blocking(move || {
+        decoder::extract_grid(&sfc_blob, &sfc_pattern, grid_spec_sfc)
+    })
+    .await
+    .expect("blocking join")?;
+
+    let grid_spec_prs = grid_spec;
+    let prs_grid = tokio::task::spawn_blocking(move || {
+        decoder::extract_grid(&prs_blob, &prs_pattern, grid_spec_prs)
+    })
+    .await
+    .expect("blocking join")?;
+
+    let merged = merge_grids(sfc_grid, prs_grid);
+    let point_count = merged.len() as u32;
+
+    // Score every point × every band; one ScorePoint per (cell, band).
+    let bands = band_config::all_bands();
+    let mut per_band: HashMap<u32, Vec<ScorePoint>> =
+        HashMap::with_capacity(bands.len());
+
+    for (key, cell) in &merged {
+        let (lat, lon) = decoder::key_to_latlon(*key);
+        let conditions = match cell_to_conditions(cell, lat, lon, &valid_time) {
+            Some(c) => c,
+            None => continue,
+        };
+        let invariants = scorer::precompute_band_invariants(&conditions);
+        for band in bands {
+            let r = scorer::composite_score_with(&conditions, band, Some(invariants));
+            per_band
+                .entry(band.freq_mhz)
+                .or_default()
+                .push(ScorePoint { lat, lon, score: r.score });
+        }
+    }
+
+    let scores_dir = scores_dir.to_path_buf();
+    let mut files_written = 0;
+    for (band_mhz, scores) in &per_band {
+        let dir = scores_dir.clone();
+        let band_mhz = *band_mhz;
+        let scores = scores.clone();
+        tokio::task::spawn_blocking(move || {
+            scores_file::write_atomic(&dir, band_mhz, valid_time, &scores)
+        })
+        .await
+        .expect("blocking join")?;
+        files_written += 1;
+    }
+
+    Ok(ChainStepStats {
+        score_files_written: files_written,
+        point_count,
+        band_count: bands.len() as u32,
+    })
+}
+
+/// wgrib2 `-match` regex: `":(A|B|C):"`. Var names only — levels are
+/// post-filtered when we read the binary back.
+fn match_pattern(wanted: &[(String, String)]) -> String {
+    let mut vars: Vec<&str> = wanted.iter().map(|(v, _)| v.as_str()).collect();
+    vars.sort();
+    vars.dedup();
+    format!(":({}):", vars.join("|"))
+}
+
+fn merge_grids(mut sfc: PointGrid, prs: PointGrid) -> PointGrid {
+    for (k, v) in prs {
+        sfc.entry(k).or_default().extend(v);
+    }
+    sfc
+}
+
+fn cell_to_conditions(
+    cell: &CellValues,
+    lat: f64,
+    lon: f64,
+    valid_time: &DateTime<Utc>,
+) -> Option<Conditions> {
+    let tmp_k = cell.get("TMP:2 m above ground").copied()?;
+    let dpt_k = cell.get("DPT:2 m above ground").copied()?;
+    let temp_c = (tmp_k - 273.15) as f64;
+    let dewpoint_c = (dpt_k - 273.15) as f64;
+    let temp_f = scorer::c_to_f(temp_c);
+    let dewpoint_f = scorer::c_to_f(dewpoint_c);
+    let abs_humidity = scorer::absolute_humidity(temp_c, dewpoint_c);
+
+    let wind_speed_kts = match (
+        cell.get("UGRD:10 m above ground").copied(),
+        cell.get("VGRD:10 m above ground").copied(),
+    ) {
+        (Some(u), Some(v)) => Some(scorer::wind_speed_kts(u as f64, v as f64)),
+        _ => None,
+    };
+
+    let sky_cover_pct = cell.get("TCDC:entire atmosphere").copied().map(|v| v as f64);
+    let pwat_mm = cell
+        .get("PWAT:entire atmosphere (considered as a single layer)")
+        .copied()
+        .map(|v| v as f64);
+    let pressure_mb = cell
+        .get("PRES:surface")
+        .copied()
+        .map(|pa| pa as f64 / 100.0);
+    let rain_rate_mmhr = cell
+        .get("APCP:surface")
+        .copied()
+        .map(|mm| mm as f64)
+        .filter(|v| *v > 0.0);
+    let bl_depth_m = cell.get("HPBL:surface").copied().map(|v| v as f64);
+
+    let levels: Vec<Level> = fetcher::GRID_PRESSURE_LEVELS
+        .iter()
+        .filter_map(|&p| {
+            let pres_mb = p as f64;
+            let t = cell.get(&format!("TMP:{p} mb")).copied()?;
+            let d = cell.get(&format!("DPT:{p} mb")).copied();
+            let h = cell.get(&format!("HGT:{p} mb")).copied()?;
+            Some(Level {
+                pres_mb,
+                hght_m: h as f64,
+                tmpc: (t - 273.15) as f64,
+                dwpc: d.map(|v| (v - 273.15) as f64),
+            })
+        })
+        .collect();
+    let min_refractivity_gradient = sounding_params::min_refractivity_gradient(levels);
+
+    Some(Conditions {
+        abs_humidity,
+        temp_f,
+        dewpoint_f,
+        wind_speed_kts,
+        sky_cover_pct,
+        utc_hour: valid_time.hour() as u8,
+        utc_minute: valid_time.minute() as u8,
+        month: valid_time.month() as u8,
+        longitude: lon,
+        latitude: Some(lat),
+        pressure_mb,
+        prev_pressure_mb: None,
+        rain_rate_mmhr,
+        min_refractivity_gradient,
+        bl_depth_m,
+        pwat_mm,
+        best_duct_band_ghz: None,
+        bulk_richardson: None,
+    })
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn match_pattern_dedups_vars() {
+        let wanted = vec![
+            ("TMP".into(), "2 m above ground".into()),
+            ("DPT".into(), "2 m above ground".into()),
+            ("TMP".into(), "1000 mb".into()),
+        ];
+        assert_eq!(match_pattern(&wanted), ":(DPT|TMP):");
+    }
+
+    #[test]
+    fn cell_to_conditions_maps_fields() {
+        use chrono::TimeZone;
+        let mut cell = CellValues::new();
+        cell.insert("TMP:2 m above ground".into(), 298.15); // 25 °C
+        cell.insert("DPT:2 m above ground".into(), 293.15); // 20 °C
+        cell.insert("UGRD:10 m above ground".into(), 3.0);
+        cell.insert("VGRD:10 m above ground".into(), 4.0);
+        cell.insert("TCDC:entire atmosphere".into(), 30.0);
+        cell.insert("PRES:surface".into(), 101_000.0);
+        cell.insert("HPBL:surface".into(), 400.0);
+        cell.insert("PWAT:entire atmosphere (considered as a single layer)".into(), 25.0);
+
+        let vt = Utc.with_ymd_and_hms(2026, 6, 15, 18, 0, 0).unwrap();
+        let c = cell_to_conditions(&cell, 32.0, -97.0, &vt).unwrap();
+        assert!((c.temp_f - 77.0).abs() < 0.1);
+        assert!((c.dewpoint_f - 68.0).abs() < 0.1);
+        assert!((c.wind_speed_kts.unwrap() - 9.72).abs() < 0.1);
+        assert!((c.pressure_mb.unwrap() - 1010.0).abs() < 0.01);
+        assert_eq!(c.sky_cover_pct, Some(30.0));
+        assert_eq!(c.bl_depth_m, Some(400.0));
+        assert_eq!(c.pwat_mm, Some(25.0));
+        assert_eq!(c.month, 6);
+        assert_eq!(c.longitude, -97.0);
+    }
+
+    #[test]
+    fn cell_missing_surface_returns_none() {
+        use chrono::TimeZone;
+        let cell = CellValues::new();
+        let vt = Utc.with_ymd_and_hms(2026, 6, 15, 18, 0, 0).unwrap();
+        assert!(cell_to_conditions(&cell, 32.0, -97.0, &vt).is_none());
+    }
+
+    #[test]
+    fn rejects_forecast_hour_zero() {
+        use chrono::TimeZone;
+        let client = HrrrClient::default_base().unwrap();
+        let dir = tempfile::tempdir().unwrap();
+        let step = ChainStepInput {
+            run_time: Utc.with_ymd_and_hms(2026, 4, 19, 15, 0, 0).unwrap(),
+            forecast_hour: 0,
+        };
+        let rt = tokio::runtime::Runtime::new().unwrap();
+        let err = rt.block_on(run_chain_step(&client, dir.path(), &step)).unwrap_err();
+        assert!(matches!(err, PipelineError::F00Reserved));
+    }
+}

rust/prop_grid_rs/src/region.rs

@@ -0,0 +1,105 @@
+//! Climatological region lookup. 1:1 port of
+//! `lib/microwaveprop/propagation/region.ex`.
+
+#[derive(Debug, Clone, Copy, PartialEq, Eq, Hash)]
+pub enum Region {
+    GulfCoast,
+    Southeast,
+    SouthernPlains,
+    CornBelt,
+    Northeast,
+    DesertSouthwest,
+    PacificNorthwest,
+    MountainWest,
+    Other,
+}
+
+/// Lat min (inclusive), lat max (exclusive), lon min (inclusive), lon max (exclusive).
+struct BBox(Region, f64, f64, f64, f64);
+
+// Ordered to match Elixir's `Enum.find_value` short-circuit.
+const REGIONS: &[BBox] = &[
+    BBox(Region::GulfCoast, 25.0, 32.0, -100.0, -80.0),
+    BBox(Region::Southeast, 30.0, 37.0, -90.0, -75.0),
+    BBox(Region::SouthernPlains, 32.0, 38.0, -105.0, -93.0),
+    BBox(Region::CornBelt, 38.0, 48.0, -100.0, -82.0),
+    BBox(Region::Northeast, 38.0, 48.0, -82.0, -67.0),
+    BBox(Region::DesertSouthwest, 30.0, 38.0, -120.0, -105.0),
+    BBox(Region::PacificNorthwest, 42.0, 50.0, -125.0, -115.0),
+    BBox(Region::MountainWest, 38.0, 48.0, -115.0, -100.0),
+];
+
+pub fn for_point(lat: f64, lon: f64) -> Region {
+    for bbox in REGIONS {
+        let BBox(name, lat_min, lat_max, lon_min, lon_max) = *bbox;
+        if lat >= lat_min && lat < lat_max && lon >= lon_min && lon < lon_max {
+            return name;
+        }
+    }
+    Region::Other
+}
+
+/// Multiplier applied to the band's `seasonal_base` score. Unknown
+/// region/month combinations return 1.0. Range [0.7, 1.3].
+pub fn seasonal_adjustment(region: Region, month: u8) -> f64 {
+    match (region, month) {
+        (Region::GulfCoast, 6) => 0.95,
+        (Region::GulfCoast, 7) => 0.95,
+        (Region::GulfCoast, 8) => 1.15,
+        (Region::GulfCoast, 9) => 1.10,
+        (Region::CornBelt, 6) => 1.05,
+        (Region::CornBelt, 7) => 0.85,
+        (Region::CornBelt, 8) => 0.80,
+        (Region::CornBelt, 9) => 0.95,
+        (Region::Southeast, 7) => 0.97,
+        (Region::Southeast, 8) => 1.08,
+        (Region::SouthernPlains, 8) => 1.05,
+        (Region::DesertSouthwest, 7) => 1.10,
+        (Region::DesertSouthwest, 8) => 1.10,
+        (Region::DesertSouthwest, 9) => 1.05,
+        (Region::PacificNorthwest, 6) => 1.15,
+        (Region::PacificNorthwest, 7) => 1.20,
+        (Region::PacificNorthwest, 8) => 1.20,
+        (Region::PacificNorthwest, 9) => 1.10,
+        _ => 1.0,
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn gulf_coast_points() {
+        // Houston ≈ (29.8, -95.4) — Gulf Coast bbox.
+        assert_eq!(for_point(29.8, -95.4), Region::GulfCoast);
+    }
+
+    #[test]
+    fn corn_belt_points() {
+        // Des Moines ≈ (41.6, -93.6) — Corn Belt bbox.
+        assert_eq!(for_point(41.6, -93.6), Region::CornBelt);
+    }
+
+    #[test]
+    fn non_conus_returns_other() {
+        // Alaska (61.2, -149.9) — outside every bbox.
+        assert_eq!(for_point(61.2, -149.9), Region::Other);
+    }
+
+    #[test]
+    fn adjustments_match_elixir_table() {
+        assert_eq!(seasonal_adjustment(Region::GulfCoast, 8), 1.15);
+        assert_eq!(seasonal_adjustment(Region::CornBelt, 7), 0.85);
+        assert_eq!(seasonal_adjustment(Region::PacificNorthwest, 7), 1.20);
+        assert_eq!(seasonal_adjustment(Region::Other, 8), 1.0);
+        assert_eq!(seasonal_adjustment(Region::CornBelt, 1), 1.0);
+    }
+
+    #[test]
+    fn precedence_matches_elixir_ordering() {
+        // (30.5, -90.0) is inside BOTH gulf_coast (25..32, -100..-80) and
+        // southeast (30..37, -90..-75). Elixir hits gulf_coast first.
+        assert_eq!(for_point(30.5, -90.0), Region::GulfCoast);
+    }
+}

rust/prop_grid_rs/src/scorer.rs

@@ -0,0 +1,949 @@
+//! Propagation scorer — 1:1 port of `lib/microwaveprop/propagation/scorer.ex`.
+//!
+//! Every factor returns a 0..=100 integer score. The composite is
+//! `round(Σ factor · weight)` with weights from `band_config`. All
+//! thresholds live in `band_config` / `region` — nothing magic here.
+//!
+//! Behavior parity tests mirror the Elixir `ScorerTest` suite line-by-line;
+//! integer scores match exactly.
+//!
+//! Elixir `Kernel.round/1` and Rust `f64::round` both use round-half-away-
+//! from-zero, so no custom rounding helper is needed.
+
+use crate::band_config::{
+    BandConfig, HumidityEffect, Weights, DEFAULT_WEIGHTS,
+    HUMIDITY_BENEFICIAL_DEFAULT, HUMIDITY_BENEFICIAL_THRESHOLDS,
+    REFRACTIVITY_DEFAULT, REFRACTIVITY_THRESHOLDS, SUNRISE_TABLE,
+};
+use crate::region;
+
+const BULK_RICHARDSON_STABLE_MAX: f64 = 25.0;
+
+/// Inputs to `composite_score`. All f64 everywhere to stay close to
+/// Erlang's single-float world.
+#[derive(Debug, Clone, Default)]
+pub struct Conditions {
+    pub abs_humidity: f64,
+    pub temp_f: f64,
+    pub dewpoint_f: f64,
+    pub wind_speed_kts: Option<f64>,
+    pub sky_cover_pct: Option<f64>,
+    pub utc_hour: u8,
+    pub utc_minute: u8,
+    pub month: u8,
+    pub longitude: f64,
+    pub latitude: Option<f64>,
+    pub pressure_mb: Option<f64>,
+    pub prev_pressure_mb: Option<f64>,
+    pub rain_rate_mmhr: Option<f64>,
+    pub min_refractivity_gradient: Option<f64>,
+    pub bl_depth_m: Option<f64>,
+    pub pwat_mm: Option<f64>,
+    pub best_duct_band_ghz: Option<f64>,
+    pub bulk_richardson: Option<f64>,
+}
+
+#[derive(Debug, Clone, Copy)]
+pub struct BandInvariants {
+    pub tod: i32,
+    pub sky: i32,
+    pub wind: i32,
+    pub pressure: i32,
+}
+
+#[derive(Debug, Clone)]
+pub struct Factors {
+    pub humidity: i32,
+    pub time_of_day: i32,
+    pub td_depression: i32,
+    pub refractivity: i32,
+    pub sky: i32,
+    pub season: i32,
+    pub wind: i32,
+    pub rain: i32,
+    pub pwat: i32,
+    pub pressure: i32,
+}
+
+#[derive(Debug, Clone)]
+pub struct Composite {
+    pub score: i32,
+    pub factors: Factors,
+}
+
+// ── Helpers ──────────────────────────────────────────────────────────
+
+pub fn f_to_c(f: f64) -> f64 {
+    (f - 32.0) * 5.0 / 9.0
+}
+
+pub fn c_to_f(c: f64) -> f64 {
+    c * 9.0 / 5.0 + 32.0
+}
+
+pub fn absolute_humidity(temp_c: f64, dewpoint_c: f64) -> f64 {
+    let e_sat = 6.112 * (17.67 * dewpoint_c / (dewpoint_c + 243.5)).exp();
+    217.0 * e_sat / (temp_c + 273.15)
+}
+
+pub fn wind_speed_kts(u_ms: f64, v_ms: f64) -> f64 {
+    (u_ms * u_ms + v_ms * v_ms).sqrt() * 1.94384
+}
+
+pub fn precip_to_rate_mmhr(mm: Option<f64>) -> f64 {
+    match mm {
+        Some(v) if v > 0.0 => v,
+        _ => 0.0,
+    }
+}
+
+/// Marshall-Palmer Z-R: `Z = 200 · R^1.6` → `R = (Z/200)^(1/1.6)`, `Z = 10^(dBZ/10)`.
+/// Clips below 5 dBZ to 0 (ground clutter) and above 150 mm/hr (hail).
+pub fn dbz_to_rain_rate_mmhr(dbz: Option<f64>) -> f64 {
+    match dbz {
+        None => 0.0,
+        Some(v) if v < 5.0 => 0.0,
+        Some(v) => {
+            let z = 10f64.powf(v / 10.0);
+            (z / 200.0).powf(1.0 / 1.6).min(150.0)
+        }
+    }
+}
+
+fn clamp_score_f(v: f64) -> i32 {
+    (v.round() as i64).clamp(0, 100) as i32
+}
+
+fn clamp_score(v: i32) -> i32 {
+    v.clamp(0, 100)
+}
+
+// ── Factor 1: humidity ───────────────────────────────────────────────
+
+pub fn score_humidity(abs_humidity: f64, band: &BandConfig) -> i32 {
+    match band.humidity_effect {
+        HumidityEffect::Beneficial => HUMIDITY_BENEFICIAL_THRESHOLDS
+            .iter()
+            .find(|(max, _)| abs_humidity < *max as f64)
+            .map(|(_, s)| *s)
+            .unwrap_or(HUMIDITY_BENEFICIAL_DEFAULT),
+        HumidityEffect::Harmful => {
+            let r = abs_humidity * band.humidity_penalty;
+            if r <= 6.0 {
+                100
+            } else if r <= 9.0 {
+                (95.0 - (r - 6.0) / 3.0 * 20.0).round() as i32
+            } else if r <= 13.0 {
+                (75.0 - (r - 9.0) / 4.0 * 30.0).round() as i32
+            } else if r <= 18.0 {
+                (45.0 - (r - 13.0) / 5.0 * 35.0).round() as i32
+            } else {
+                ((10.0 - (r - 18.0) * 2.0).round() as i32).max(0)
+            }
+        }
+    }
+}
+
+// ── Factor 2: time of day ────────────────────────────────────────────
+
+pub fn score_time_of_day(
+    utc_hour: u8,
+    utc_minute: u8,
+    month: u8,
+    longitude: f64,
+) -> (i32, &'static str) {
+    let offset = longitude / 15.0;
+    let raw = utc_hour as f64 + utc_minute as f64 / 60.0 + offset + 24.0;
+    // Match Elixir :math.fmod/2 — same semantics as fmod.
+    let local = raw.rem_euclid(24.0);
+    let sunrise = SUNRISE_TABLE[(month - 1) as usize];
+    let d = local - sunrise;
+
+    if (-1.5..=1.5).contains(&d) {
+        (100, "Peak — inversion maximum")
+    } else if d > 1.5 && d <= 3.0 {
+        (78, "Good — inversion eroding")
+    } else if d > -3.0 && d < -1.5 {
+        (82, "Pre-dawn — inversion building")
+    } else if d > 3.0 && d <= 6.0 {
+        (38, "Marginal — boundary layer mixing")
+    } else if local >= 20.0 || local <= 1.0 {
+        (72, "Evening — cooling, inversion reforming")
+    } else if d > 6.0 {
+        (18, "Afternoon — full convective mixing")
+    } else {
+        (55, "Night — gradual cooling")
+    }
+}
+
+// ── Factor 3: T-Td depression ────────────────────────────────────────
+
+pub fn score_td_depression(temp_f: f64, dewpoint_f: f64, band: &BandConfig) -> i32 {
+    let dep = temp_f - dewpoint_f;
+    match band.humidity_effect {
+        HumidityEffect::Beneficial => {
+            if dep < 3.0 {
+                40
+            } else if dep < 8.0 {
+                75
+            } else if dep < 14.0 {
+                85
+            } else if dep < 22.0 {
+                70
+            } else {
+                55
+            }
+        }
+        HumidityEffect::Harmful => {
+            if dep > 22.0 {
+                96
+            } else if dep > 14.0 {
+                80
+            } else if dep > 8.0 {
+                60
+            } else if dep > 4.0 {
+                38
+            } else {
+                18
+            }
+        }
+    }
+}
+
+// ── Factor 4: refractivity gradient (+ HPBL multiplier + native duct boost) ──
+
+pub fn score_refractivity(
+    min_gradient: Option<f64>,
+    bl_depth_m: Option<f64>,
+    best_duct_band_ghz: Option<f64>,
+    bulk_richardson: Option<f64>,
+    band: &BandConfig,
+) -> i32 {
+    let Some(gradient) = min_gradient else {
+        return 50;
+    };
+
+    let base_match = REFRACTIVITY_THRESHOLDS
+        .iter()
+        .find(|(max, _, _)| gradient < *max as f64);
+
+    let base = match base_match {
+        Some((_, b, h)) => match band.humidity_effect {
+            HumidityEffect::Beneficial => *b,
+            HumidityEffect::Harmful => *h,
+        },
+        None => {
+            let (b, h) = REFRACTIVITY_DEFAULT;
+            if band.humidity_effect == HumidityEffect::Beneficial {
+                b
+            } else {
+                h
+            }
+        }
+    };
+
+    let with_hpbl = apply_hpbl_multiplier(base, bl_depth_m);
+    apply_native_duct_boost(with_hpbl, best_duct_band_ghz, bulk_richardson, band.freq_mhz)
+}
+
+fn apply_hpbl_multiplier(base: i32, hpbl: Option<f64>) -> i32 {
+    let mul = match hpbl {
+        None => return base,
+        Some(v) if v < 200.0 => 1.10,
+        Some(v) if v < 500.0 => 1.05,
+        Some(v) if v < 1500.0 => 1.0,
+        Some(v) if v < 2000.0 => 0.92,
+        Some(_) => 0.78,
+    };
+    clamp_score_f(base as f64 * mul)
+}
+
+fn apply_native_duct_boost(
+    base: i32,
+    best_duct_band_ghz: Option<f64>,
+    bulk_richardson: Option<f64>,
+    freq_mhz: u32,
+) -> i32 {
+    let Some(duct_band_ghz) = best_duct_band_ghz else {
+        return base;
+    };
+    let target_ghz = freq_mhz as f64 / 1000.0;
+    let stable = match bulk_richardson {
+        None => true,
+        Some(r) => r < BULK_RICHARDSON_STABLE_MAX,
+    };
+    if duct_band_ghz >= target_ghz && stable {
+        clamp_score_f(base as f64 * 1.15)
+    } else {
+        base
+    }
+}
+
+// ── Factor 5: sky cover ──────────────────────────────────────────────
+
+pub fn score_sky(pct: Option<f64>) -> i32 {
+    match pct {
+        None => 50,
+        Some(p) if p <= 6.0 => 100,
+        Some(p) if p <= 25.0 => 88,
+        Some(p) if p <= 50.0 => 60,
+        Some(p) if p <= 87.0 => 25,
+        Some(_) => 5,
+    }
+}
+
+// ── Factor 6: season ─────────────────────────────────────────────────
+
+pub fn score_season(month: u8, lat: Option<f64>, lon: Option<f64>, band: &BandConfig) -> i32 {
+    let idx = (month - 1) as usize;
+    let base = band.seasonal_base[idx];
+    let adj = band.seasonal_adj[idx];
+
+    let region_mult = match (lat, lon) {
+        (Some(la), Some(lo)) => region::seasonal_adjustment(region::for_point(la, lo), month),
+        _ => 1.0,
+    };
+
+    let raw = (base + adj) as f64 * region_mult;
+    clamp_score_f(raw)
+}
+
+// ── Factor 7: wind ───────────────────────────────────────────────────
+
+pub fn score_wind(speed_kts: Option<f64>) -> i32 {
+    match speed_kts {
+        None => 50,
+        Some(s) if s < 5.0 => 100,
+        Some(s) if s < 10.0 => 90,
+        Some(s) if s < 15.0 => 75,
+        Some(s) if s < 20.0 => 55,
+        Some(s) if s < 25.0 => 35,
+        Some(_) => 15,
+    }
+}
+
+// ── Factor 8: rain attenuation (ITU-R P.838) ────────────────────────
+
+pub fn score_rain(rate_mmhr: Option<f64>, band: &BandConfig) -> i32 {
+    match rate_mmhr {
+        None => 100,
+        Some(0.0) => 100,
+        Some(v) => {
+            let gamma = band.rain_k * v.powf(band.rain_alpha);
+            if gamma < 0.1 {
+                95
+            } else if gamma < 0.5 {
+                75
+            } else if gamma < 1.0 {
+                50
+            } else if gamma < 2.0 {
+                25
+            } else if gamma < 5.0 {
+                10
+            } else {
+                0
+            }
+        }
+    }
+}
+
+// ── Factor 9: precipitable water ────────────────────────────────────
+
+pub fn score_pwat(pwat_mm: Option<f64>, band: &BandConfig) -> i32 {
+    let Some(v) = pwat_mm else { return 60 };
+    match band.humidity_effect {
+        HumidityEffect::Beneficial => {
+            if v < 10.0 {
+                55
+            } else if v < 20.0 {
+                75
+            } else if v < 30.0 {
+                90
+            } else if v < 40.0 {
+                70
+            } else {
+                50
+            }
+        }
+        HumidityEffect::Harmful => {
+            if v < 10.0 {
+                95
+            } else if v < 20.0 {
+                80
+            } else if v < 30.0 {
+                60
+            } else if v < 40.0 {
+                35
+            } else {
+                15
+            }
+        }
+    }
+}
+
+// ── Factor 10: pressure ─────────────────────────────────────────────
+
+pub fn score_pressure(current_mb: Option<f64>, previous_mb: Option<f64>) -> i32 {
+    let Some(current) = current_mb else { return 50 };
+    match previous_mb {
+        None => {
+            if current < 980.0 {
+                88
+            } else if current < 990.0 {
+                82
+            } else if current < 1000.0 {
+                70
+            } else if current < 1010.0 {
+                55
+            } else if current < 1020.0 {
+                40
+            } else {
+                30
+            }
+        }
+        Some(prev) => {
+            let delta = current - prev;
+            if delta > 2.5 {
+                80
+            } else if delta > 0.8 {
+                70
+            } else if delta > -0.5 {
+                60
+            } else if delta > -2.0 {
+                65
+            } else {
+                45
+            }
+        }
+    }
+}
+
+// ── Composite ───────────────────────────────────────────────────────
+
+pub fn precompute_band_invariants(c: &Conditions) -> BandInvariants {
+    let (tod, _) = score_time_of_day(c.utc_hour, c.utc_minute, c.month, c.longitude);
+    BandInvariants {
+        tod,
+        sky: score_sky(c.sky_cover_pct),
+        wind: score_wind(c.wind_speed_kts),
+        pressure: score_pressure(c.pressure_mb, c.prev_pressure_mb),
+    }
+}
+
+pub fn composite_score(c: &Conditions, band: &BandConfig) -> Composite {
+    composite_score_with(c, band, None)
+}
+
+pub fn composite_score_with(
+    c: &Conditions,
+    band: &BandConfig,
+    precomputed: Option<BandInvariants>,
+) -> Composite {
+    let inv = precomputed.unwrap_or_else(|| precompute_band_invariants(c));
+
+    let factors = Factors {
+        humidity: score_humidity(c.abs_humidity, band),
+        time_of_day: inv.tod,
+        td_depression: score_td_depression(c.temp_f, c.dewpoint_f, band),
+        refractivity: score_refractivity(
+            c.min_refractivity_gradient,
+            c.bl_depth_m,
+            c.best_duct_band_ghz,
+            c.bulk_richardson,
+            band,
+        ),
+        sky: inv.sky,
+        season: score_season(c.month, c.latitude, Some(c.longitude).filter(|_| c.latitude.is_some()), band),
+        wind: inv.wind,
+        rain: score_rain(c.rain_rate_mmhr, band),
+        pwat: score_pwat(c.pwat_mm, band),
+        pressure: inv.pressure,
+    };
+
+    let w = band.weights.unwrap_or(DEFAULT_WEIGHTS);
+    let weighted = weighted_sum(&factors, &w);
+    Composite {
+        score: clamp_score_f(weighted),
+        factors,
+    }
+}
+
+fn weighted_sum(f: &Factors, w: &Weights) -> f64 {
+    f.humidity as f64 * w.humidity
+        + f.time_of_day as f64 * w.time_of_day
+        + f.td_depression as f64 * w.td_depression
+        + f.refractivity as f64 * w.refractivity
+        + f.sky as f64 * w.sky
+        + f.season as f64 * w.season
+        + f.wind as f64 * w.wind
+        + f.rain as f64 * w.rain
+        + f.pressure as f64 * w.pressure
+        + f.pwat as f64 * w.pwat
+}
+
+/// Commercial-link inverse-sensor boost. Not used in the grid hot path
+/// (f00-only — Elixir keeps that) but ported so unit-level correctness
+/// stays testable from the Rust side.
+pub fn commercial_link_boost(score: i32, n_links: u32, degradation_db: f64) -> i32 {
+    if n_links == 0 || degradation_db < 3.0 {
+        return clamp_score(score);
+    }
+    if degradation_db < 8.0 {
+        let bonus = 2.0 + (degradation_db - 3.0) * 8.0 / 5.0;
+        clamp_score_f(score as f64 + bonus)
+    } else {
+        let bonus = (10.0 + (degradation_db - 8.0) * 15.0 / 8.0).min(25.0);
+        clamp_score_f(score as f64 + bonus)
+    }
+}
+
+// ── Tests (mirror Elixir ScorerTest) ────────────────────────────────
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+    use crate::band_config;
+
+    fn b10g() -> &'static BandConfig {
+        band_config::get(10_000).unwrap()
+    }
+    fn b24g() -> &'static BandConfig {
+        band_config::get(24_000).unwrap()
+    }
+    fn b75g() -> &'static BandConfig {
+        band_config::get(75_000).unwrap()
+    }
+
+    const EAST_LON: f64 = -75.0;
+
+    #[test]
+    fn f_to_c_boundaries() {
+        assert!((f_to_c(32.0) - 0.0).abs() < 0.01);
+        assert!((f_to_c(212.0) - 100.0).abs() < 0.01);
+    }
+
+    #[test]
+    fn c_to_f_boundaries() {
+        assert!((c_to_f(0.0) - 32.0).abs() < 0.01);
+        assert!((c_to_f(100.0) - 212.0).abs() < 0.01);
+    }
+
+    #[test]
+    fn absolute_humidity_typical_summer() {
+        let ah = absolute_humidity(25.0, 20.0);
+        assert!(ah > 15.0 && ah < 20.0, "{ah}");
+    }
+
+    #[test]
+    fn absolute_humidity_cold_dry() {
+        let ah = absolute_humidity(0.0, -5.0);
+        assert!(ah > 2.0 && ah < 5.0, "{ah}");
+    }
+
+    #[test]
+    fn wind_speed_3_4_kts() {
+        assert!((wind_speed_kts(3.0, 4.0) - 9.72).abs() < 0.1);
+    }
+
+    #[test]
+    fn precip_to_rate_handles_nil_zero_negative() {
+        assert_eq!(precip_to_rate_mmhr(Some(2.5)), 2.5);
+        assert_eq!(precip_to_rate_mmhr(Some(0.0)), 0.0);
+        assert_eq!(precip_to_rate_mmhr(Some(-1.0)), 0.0);
+        assert_eq!(precip_to_rate_mmhr(None), 0.0);
+    }
+
+    #[test]
+    fn dbz_to_rain_rate_clips_and_interpolates() {
+        assert_eq!(dbz_to_rain_rate_mmhr(None), 0.0);
+        assert_eq!(dbz_to_rain_rate_mmhr(Some(3.0)), 0.0);
+        assert!((dbz_to_rain_rate_mmhr(Some(20.0)) - 0.66).abs() < 0.05);
+        assert!((dbz_to_rain_rate_mmhr(Some(30.0)) - 2.7).abs() < 0.2);
+        assert!((dbz_to_rain_rate_mmhr(Some(45.0)) - 23.7).abs() < 1.0);
+        assert!(dbz_to_rain_rate_mmhr(Some(55.0)) <= 150.0);
+        assert!(dbz_to_rain_rate_mmhr(Some(65.0)) <= 150.0);
+    }
+
+    // ── humidity ─────────────────────────────────────────────────
+
+    #[test]
+    fn humidity_beneficial_table() {
+        assert_eq!(score_humidity(3.0, b10g()), 55);
+        assert_eq!(score_humidity(9.0, b10g()), 82);
+        assert_eq!(score_humidity(16.0, b10g()), 95);
+        assert_eq!(score_humidity(20.0, b10g()), 88);
+        assert_eq!(score_humidity(25.0, b10g()), 75);
+    }
+
+    #[test]
+    fn humidity_harmful_piecewise() {
+        assert_eq!(score_humidity(2.0, b24g()), 100);
+        assert_eq!(score_humidity(5.0, b24g()), 82);
+        assert_eq!(score_humidity(10.0, b24g()), 24);
+        assert_eq!(score_humidity(20.0, b24g()), 0);
+    }
+
+    // ── time of day ──────────────────────────────────────────────
+
+    #[test]
+    fn time_of_day_dawn_peak() {
+        let (s, l) = score_time_of_day(11, 15, 6, EAST_LON);
+        assert_eq!(s, 100);
+        assert!(l.contains("Peak"));
+    }
+
+    #[test]
+    fn time_of_day_afternoon() {
+        let (s, _) = score_time_of_day(22, 0, 6, EAST_LON);
+        assert_eq!(s, 18);
+    }
+
+    #[test]
+    fn time_of_day_pre_dawn() {
+        let (s, l) = score_time_of_day(9, 0, 6, EAST_LON);
+        assert_eq!(s, 82);
+        assert!(l.contains("Pre-dawn"));
+    }
+
+    #[test]
+    fn time_of_day_evening() {
+        let (s, l) = score_time_of_day(1, 0, 6, EAST_LON);
+        assert_eq!(s, 72);
+        assert!(l.contains("Evening"));
+    }
+
+    #[test]
+    fn time_of_day_western_longitude_shifts_earlier() {
+        let (s, _) = score_time_of_day(13, 24, 1, -90.0);
+        assert_eq!(s, 100);
+    }
+
+    #[test]
+    fn time_of_day_same_utc_different_longitudes() {
+        let (east, _) = score_time_of_day(18, 0, 6, -75.0);
+        let (west, _) = score_time_of_day(18, 0, 6, -120.0);
+        assert!(west > east);
+    }
+
+    // ── td depression ────────────────────────────────────────────
+
+    #[test]
+    fn td_beneficial() {
+        assert_eq!(score_td_depression(72.0, 70.0, b10g()), 40);
+        assert_eq!(score_td_depression(80.0, 70.0, b10g()), 85);
+        assert_eq!(score_td_depression(100.0, 50.0, b10g()), 55);
+    }
+
+    #[test]
+    fn td_harmful() {
+        assert_eq!(score_td_depression(72.0, 70.0, b24g()), 18);
+        assert_eq!(score_td_depression(80.0, 70.0, b24g()), 60);
+        assert_eq!(score_td_depression(100.0, 50.0, b24g()), 96);
+    }
+
+    // ── refractivity ─────────────────────────────────────────────
+
+    const BASELINE_BL: Option<f64> = Some(750.0);
+
+    #[test]
+    fn refractivity_strong_gradient_beneficial() {
+        assert_eq!(score_refractivity(Some(-600.0), BASELINE_BL, None, None, b10g()), 98);
+    }
+
+    #[test]
+    fn refractivity_strong_gradient_harmful() {
+        assert_eq!(score_refractivity(Some(-250.0), BASELINE_BL, None, None, b24g()), 85);
+    }
+
+    #[test]
+    fn refractivity_moderate_gradient_beneficial() {
+        assert_eq!(score_refractivity(Some(-160.0), BASELINE_BL, None, None, b10g()), 92);
+    }
+
+    #[test]
+    fn refractivity_nil_gradient_returns_50() {
+        assert_eq!(score_refractivity(None, BASELINE_BL, None, None, b10g()), 50);
+    }
+
+    #[test]
+    fn refractivity_nil_bl_no_multiplier() {
+        assert_eq!(score_refractivity(Some(-160.0), None, None, None, b10g()), 92);
+    }
+
+    #[test]
+    fn shallow_bl_boosts_score() {
+        let shallow = score_refractivity(Some(-100.0), Some(150.0), None, None, b10g());
+        let baseline = score_refractivity(Some(-100.0), BASELINE_BL, None, None, b10g());
+        assert!(shallow > baseline);
+        assert!(shallow <= 100);
+    }
+
+    #[test]
+    fn deep_bl_penalises_score() {
+        let deep = score_refractivity(Some(-100.0), Some(2200.0), None, None, b10g());
+        let baseline = score_refractivity(Some(-100.0), BASELINE_BL, None, None, b10g());
+        assert!(deep < baseline);
+        assert!(deep >= 0);
+    }
+
+    #[test]
+    fn shallow_bl_also_lifts_default_fallback() {
+        let shallow = score_refractivity(Some(-30.0), Some(150.0), None, None, b10g());
+        let baseline = score_refractivity(Some(-30.0), BASELINE_BL, None, None, b10g());
+        assert!(shallow > baseline);
+    }
+
+    #[test]
+    fn native_duct_boosts_matching_band() {
+        let boosted = score_refractivity(Some(-80.0), Some(800.0), Some(15.0), None, b10g());
+        let plain = score_refractivity(Some(-80.0), Some(800.0), None, None, b10g());
+        assert!(boosted > plain);
+        assert!(boosted <= 100);
+    }
+
+    #[test]
+    fn native_duct_below_target_no_boost() {
+        let unchanged = score_refractivity(Some(-80.0), Some(800.0), Some(3.0), None, b10g());
+        let plain = score_refractivity(Some(-80.0), Some(800.0), None, None, b10g());
+        assert_eq!(unchanged, plain);
+    }
+
+    #[test]
+    fn richardson_gates_the_boost() {
+        let stable = score_refractivity(Some(-80.0), Some(800.0), Some(15.0), Some(12.0), b10g());
+        let plain = score_refractivity(Some(-80.0), Some(800.0), None, None, b10g());
+        assert!(stable > plain);
+
+        let turbulent =
+            score_refractivity(Some(-80.0), Some(800.0), Some(15.0), Some(40.0), b10g());
+        assert_eq!(turbulent, plain);
+
+        let nil_r = score_refractivity(Some(-80.0), Some(800.0), Some(15.0), None, b10g());
+        let four_arity_equiv =
+            score_refractivity(Some(-80.0), Some(800.0), Some(15.0), None, b10g());
+        assert_eq!(nil_r, four_arity_equiv);
+
+        let boundary =
+            score_refractivity(Some(-80.0), Some(800.0), Some(15.0), Some(25.0), b10g());
+        assert_eq!(boundary, plain);
+    }
+
+    // ── commercial link boost ────────────────────────────────────
+
+    #[test]
+    fn commercial_link_noop_cases() {
+        assert_eq!(commercial_link_boost(75, 0, 10.0), 75);
+        assert_eq!(commercial_link_boost(75, 3, 2.0), 75);
+    }
+
+    #[test]
+    fn commercial_link_mild_boost() {
+        let b = commercial_link_boost(75, 3, 5.0);
+        assert!(b > 75 && b < 90, "{b}");
+    }
+
+    #[test]
+    fn commercial_link_strong_boost_capped() {
+        let b = commercial_link_boost(75, 3, 12.0);
+        assert!(b > 85 && b <= 100, "{b}");
+    }
+
+    // ── sky ──────────────────────────────────────────────────────
+
+    #[test]
+    fn sky_table() {
+        assert_eq!(score_sky(Some(5.0)), 100);
+        assert_eq!(score_sky(Some(20.0)), 88);
+        assert_eq!(score_sky(Some(40.0)), 60);
+        assert_eq!(score_sky(Some(75.0)), 25);
+        assert_eq!(score_sky(Some(95.0)), 5);
+        assert_eq!(score_sky(None), 50);
+    }
+
+    // ── season ───────────────────────────────────────────────────
+
+    #[test]
+    fn season_table_basic() {
+        assert_eq!(score_season(7, None, None, b10g()), 95);
+        assert_eq!(score_season(3, None, None, b10g()), 22);
+        assert_eq!(score_season(11, None, None, b24g()), 96);
+        assert_eq!(score_season(7, None, None, b24g()), 8);
+    }
+
+    #[test]
+    fn season_gulf_coast_august_boost() {
+        let no_region = score_season(8, None, None, b10g());
+        let gulf = score_season(8, Some(29.0), Some(-95.0), b10g());
+        assert!(gulf > no_region);
+    }
+
+    #[test]
+    fn season_corn_belt_august_penalty() {
+        let no_region = score_season(8, None, None, b10g());
+        let iowa = score_season(8, Some(42.0), Some(-93.0), b10g());
+        assert!(iowa < no_region);
+    }
+
+    // ── wind ─────────────────────────────────────────────────────
+
+    #[test]
+    fn wind_table() {
+        assert_eq!(score_wind(Some(3.0)), 100);
+        assert_eq!(score_wind(Some(8.0)), 90);
+        assert_eq!(score_wind(Some(12.0)), 75);
+        assert_eq!(score_wind(Some(22.0)), 35);
+        assert_eq!(score_wind(Some(30.0)), 15);
+        assert_eq!(score_wind(None), 50);
+    }
+
+    // ── rain ─────────────────────────────────────────────────────
+
+    #[test]
+    fn rain_zero_and_nil_full_score() {
+        assert_eq!(score_rain(Some(0.0), b24g()), 100);
+        assert_eq!(score_rain(None, b24g()), 100);
+    }
+
+    #[test]
+    fn rain_24g_light() {
+        // gamma = 0.070 * 2.0^1.07 ≈ 0.147 → 75
+        assert_eq!(score_rain(Some(2.0), b24g()), 75);
+    }
+
+    #[test]
+    fn rain_10g_heavy_still_high() {
+        // gamma = 0.010 * 5.0^1.28 ≈ 0.076 → 95
+        assert_eq!(score_rain(Some(5.0), b10g()), 95);
+    }
+
+    #[test]
+    fn rain_75g_heavy_drops() {
+        // gamma = 0.345 * 10^0.84 ≈ 2.39 → 10
+        assert_eq!(score_rain(Some(10.0), b75g()), 10);
+    }
+
+    // ── pwat ─────────────────────────────────────────────────────
+
+    #[test]
+    fn pwat_beneficial_table() {
+        assert_eq!(score_pwat(Some(5.0), b10g()), 55);
+        assert_eq!(score_pwat(Some(15.0), b10g()), 75);
+        assert_eq!(score_pwat(Some(25.0), b10g()), 90);
+        assert_eq!(score_pwat(Some(35.0), b10g()), 70);
+        assert_eq!(score_pwat(Some(45.0), b10g()), 50);
+    }
+
+    #[test]
+    fn pwat_harmful_table() {
+        assert_eq!(score_pwat(Some(5.0), b24g()), 95);
+        assert_eq!(score_pwat(Some(15.0), b24g()), 80);
+        assert_eq!(score_pwat(Some(25.0), b24g()), 60);
+        assert_eq!(score_pwat(Some(35.0), b24g()), 35);
+        assert_eq!(score_pwat(Some(45.0), b24g()), 15);
+    }
+
+    #[test]
+    fn pwat_nil_returns_60() {
+        assert_eq!(score_pwat(None, b10g()), 60);
+        assert_eq!(score_pwat(None, b24g()), 60);
+    }
+
+    // ── pressure ─────────────────────────────────────────────────
+
+    #[test]
+    fn pressure_standalone_table() {
+        assert_eq!(score_pressure(Some(1028.0), None), 30);
+        assert_eq!(score_pressure(Some(1020.0), None), 30);
+        assert_eq!(score_pressure(Some(1000.0), None), 55);
+    }
+
+    #[test]
+    fn pressure_deltas() {
+        assert_eq!(score_pressure(Some(1020.0), Some(1015.0)), 80);
+        assert_eq!(score_pressure(Some(1016.0), Some(1015.0)), 70);
+        assert_eq!(score_pressure(Some(1015.0), Some(1015.3)), 60);
+        assert_eq!(score_pressure(Some(1014.0), Some(1015.0)), 65);
+        assert_eq!(score_pressure(Some(1010.0), Some(1015.0)), 45);
+    }
+
+    // ── composite ────────────────────────────────────────────────
+
+    fn canonical_conditions() -> Conditions {
+        Conditions {
+            abs_humidity: 10.0,
+            temp_f: 80.0,
+            dewpoint_f: 70.0,
+            wind_speed_kts: Some(5.0),
+            sky_cover_pct: Some(20.0),
+            utc_hour: 11,
+            utc_minute: 15,
+            month: 6,
+            longitude: -75.0,
+            latitude: None,
+            pressure_mb: Some(1020.0),
+            prev_pressure_mb: Some(1018.0),
+            rain_rate_mmhr: Some(0.0),
+            min_refractivity_gradient: Some(-350.0),
+            bl_depth_m: Some(400.0),
+            pwat_mm: Some(25.0),
+            best_duct_band_ghz: None,
+            bulk_richardson: None,
+        }
+    }
+
+    #[test]
+    fn composite_returns_0_100_score() {
+        let r = composite_score(&canonical_conditions(), b10g());
+        assert!(r.score >= 0 && r.score <= 100);
+    }
+
+    #[test]
+    fn composite_all_factors_populated() {
+        let r = composite_score(&canonical_conditions(), b10g());
+        let f = &r.factors;
+        for s in [
+            f.humidity, f.time_of_day, f.td_depression, f.refractivity,
+            f.sky, f.season, f.wind, f.rain, f.pwat, f.pressure,
+        ] {
+            assert!((0..=100).contains(&s), "factor out of range: {s}");
+        }
+    }
+
+    #[test]
+    fn precomputed_invariants_match_fresh() {
+        let c = canonical_conditions();
+        let inv = precompute_band_invariants(&c);
+        let fresh = composite_score(&c, b10g());
+        let reused = composite_score_with(&c, b10g(), Some(inv));
+        assert_eq!(fresh.factors.time_of_day, reused.factors.time_of_day);
+        assert_eq!(fresh.factors.sky, reused.factors.sky);
+        assert_eq!(fresh.factors.wind, reused.factors.wind);
+        assert_eq!(fresh.factors.pressure, reused.factors.pressure);
+        assert_eq!(fresh.score, reused.score);
+    }
+
+    #[test]
+    fn composite_uses_band_weights() {
+        let r = composite_score(&canonical_conditions(), b10g());
+        let w = DEFAULT_WEIGHTS;
+        let expected = r.factors.humidity as f64 * w.humidity
+            + r.factors.time_of_day as f64 * w.time_of_day
+            + r.factors.td_depression as f64 * w.td_depression
+            + r.factors.refractivity as f64 * w.refractivity
+            + r.factors.sky as f64 * w.sky
+            + r.factors.season as f64 * w.season
+            + r.factors.wind as f64 * w.wind
+            + r.factors.rain as f64 * w.rain
+            + r.factors.pwat as f64 * w.pwat
+            + r.factors.pressure as f64 * w.pressure;
+        assert!((r.score as f64 - expected.round()).abs() <= 1.0);
+    }
+
+    #[test]
+    fn composite_10g_vs_24g_differ() {
+        let c = canonical_conditions();
+        let r10 = composite_score(&c, b10g());
+        let r24 = composite_score(&c, b24g());
+        assert_ne!(r10.score, r24.score);
+    }
+}

rust/prop_grid_rs/src/scores_file.rs

@@ -0,0 +1,284 @@
+//! Score-grid file format (v1). 1:1 port of
+//! `lib/microwaveprop/propagation/scores_file.ex`.
+//!
+//! Layout (all little-endian):
+//!   magic      : 4 bytes   "NTMS"  (literal already on disk)
+//!   version    : 1 byte    0x01
+//!   band_mhz   : 4 bytes   uint32
+//!   valid_time : 8 bytes   int64 unix seconds
+//!   lat_min    : 4 bytes   float32
+//!   lon_min    : 4 bytes   float32
+//!   step_deg   : 4 bytes   float32
+//!   n_rows     : 2 bytes   uint16 (lat)
+//!   n_cols     : 2 bytes   uint16 (lon)
+//!   scores     : n_rows × n_cols bytes (uint8, 0-100 or 255 = no-data)
+//!
+//! Writes go through `rename(2)` — we write to `path.tmp.<nanos.<uniq>>`
+//! then atomically rename to the final path. On the shared NFSv4 mount
+//! this is safe for concurrent readers.
+
+use std::fs::OpenOptions;
+use std::io::{BufWriter, Write};
+use std::path::{Path, PathBuf};
+use std::sync::atomic::{AtomicU64, Ordering};
+use std::time::{SystemTime, UNIX_EPOCH};
+
+use chrono::{DateTime, Utc};
+
+use crate::grid;
+
+pub const MAGIC: &[u8; 4] = b"NTMS";
+pub const VERSION: u8 = 1;
+pub const NO_DATA: u8 = 255;
+
+static UNIQUE: AtomicU64 = AtomicU64::new(1);
+
+/// Absolute path `<base>/<band_mhz>/<iso>.ntms`.
+pub fn path_for(base_dir: &Path, band_mhz: u32, valid_time: DateTime<Utc>) -> PathBuf {
+    let iso = valid_time
+        .format("%Y-%m-%dT%H:%M:%SZ")
+        .to_string();
+    base_dir
+        .join(band_mhz.to_string())
+        .join(format!("{iso}.ntms"))
+}
+
+#[derive(Debug, thiserror::Error)]
+pub enum WriteError {
+    #[error("io: {0}")]
+    Io(#[from] std::io::Error),
+    #[error("grid dimensions exceed uint16 (rows={rows}, cols={cols})")]
+    GridTooLarge { rows: usize, cols: usize },
+}
+
+/// Encode the full on-disk representation into a `Vec<u8>`. Separated
+/// from the file I/O so tests can round-trip without a tempdir.
+pub fn encode(
+    band_mhz: u32,
+    valid_time: DateTime<Utc>,
+    scores: &[ScorePoint],
+) -> Result<Vec<u8>, WriteError> {
+    let spec = grid::wgrib2_grid_spec();
+    let n_rows: u16 = spec
+        .lat_count
+        .try_into()
+        .map_err(|_| WriteError::GridTooLarge {
+            rows: spec.lat_count,
+            cols: spec.lon_count,
+        })?;
+    let n_cols: u16 = spec
+        .lon_count
+        .try_into()
+        .map_err(|_| WriteError::GridTooLarge {
+            rows: spec.lat_count,
+            cols: spec.lon_count,
+        })?;
+
+    let row_count = n_rows as usize;
+    let col_count = n_cols as usize;
+    let mut body = vec![NO_DATA; row_count * col_count];
+
+    for s in scores {
+        let row = (((s.lat - spec.lat_start) / spec.lat_step).round()) as isize;
+        let col = (((s.lon - spec.lon_start) / spec.lon_step).round()) as isize;
+        if row < 0 || col < 0 || row as usize >= row_count || col as usize >= col_count {
+            continue;
+        }
+        body[(row as usize) * col_count + (col as usize)] = clamp_score(s.score);
+    }
+
+    let mut out =
+        Vec::with_capacity(4 + 1 + 4 + 8 + 4 + 4 + 4 + 2 + 2 + body.len());
+    out.extend_from_slice(MAGIC);
+    out.push(VERSION);
+    out.extend_from_slice(&band_mhz.to_le_bytes());
+    out.extend_from_slice(&valid_time.timestamp().to_le_bytes());
+    out.extend_from_slice(&(spec.lat_start as f32).to_le_bytes());
+    out.extend_from_slice(&(spec.lon_start as f32).to_le_bytes());
+    out.extend_from_slice(&(spec.lon_step as f32).to_le_bytes());
+    out.extend_from_slice(&n_rows.to_le_bytes());
+    out.extend_from_slice(&n_cols.to_le_bytes());
+    out.extend_from_slice(&body);
+    Ok(out)
+}
+
+/// Atomic write to `<base>/<band_mhz>/<iso>.ntms`. Creates the band
+/// subdirectory on demand.
+pub fn write_atomic(
+    base_dir: &Path,
+    band_mhz: u32,
+    valid_time: DateTime<Utc>,
+    scores: &[ScorePoint],
+) -> Result<(), WriteError> {
+    let bytes = encode(band_mhz, valid_time, scores)?;
+    let final_path = path_for(base_dir, band_mhz, valid_time);
+    let parent = final_path
+        .parent()
+        .ok_or_else(|| std::io::Error::other("path has no parent"))?;
+    std::fs::create_dir_all(parent)?;
+
+    let nanos = SystemTime::now()
+        .duration_since(UNIX_EPOCH)
+        .map(|d| d.as_nanos())
+        .unwrap_or(0);
+    let uniq = UNIQUE.fetch_add(1, Ordering::Relaxed);
+    let tmp_path = final_path.with_extension(format!("ntms.tmp.{nanos}.{uniq}"));
+
+    {
+        let file = OpenOptions::new()
+            .write(true)
+            .create_new(true)
+            .open(&tmp_path)?;
+        let mut w = BufWriter::new(file);
+        w.write_all(&bytes)?;
+        w.flush()?;
+    }
+
+    match std::fs::rename(&tmp_path, &final_path) {
+        Ok(()) => Ok(()),
+        Err(e) => {
+            let _ = std::fs::remove_file(&tmp_path);
+            Err(WriteError::Io(e))
+        }
+    }
+}
+
+#[derive(Debug, Clone, Copy)]
+pub struct ScorePoint {
+    pub lat: f64,
+    pub lon: f64,
+    pub score: i32,
+}
+
+fn clamp_score(s: i32) -> u8 {
+    if s < 0 {
+        0
+    } else if s > 100 {
+        100
+    } else {
+        s as u8
+    }
+}
+
+/// Minimal decoder used only in tests + the shadow comparator. Returns
+/// the raw row-major body plus the metadata. Mirrors the Elixir
+/// `decode/1` sans Access-behavior niceties.
+pub fn decode(bytes: &[u8]) -> Option<Decoded> {
+    use byteorder::{ByteOrder, LittleEndian};
+    if bytes.len() < 4 + 1 + 4 + 8 + 4 + 4 + 4 + 2 + 2 {
+        return None;
+    }
+    if &bytes[0..4] != MAGIC {
+        return None;
+    }
+    if bytes[4] != VERSION {
+        return None;
+    }
+    let band_mhz = LittleEndian::read_u32(&bytes[5..9]);
+    let valid_time_unix = LittleEndian::read_i64(&bytes[9..17]);
+    let lat_min = LittleEndian::read_f32(&bytes[17..21]);
+    let lon_min = LittleEndian::read_f32(&bytes[21..25]);
+    let step = LittleEndian::read_f32(&bytes[25..29]);
+    let n_rows = LittleEndian::read_u16(&bytes[29..31]);
+    let n_cols = LittleEndian::read_u16(&bytes[31..33]);
+    let body_len = (n_rows as usize) * (n_cols as usize);
+    if bytes.len() < 33 + body_len {
+        return None;
+    }
+    let valid_time = DateTime::<Utc>::from_timestamp(valid_time_unix, 0)?;
+    Some(Decoded {
+        band_mhz,
+        valid_time,
+        lat_min,
+        lon_min,
+        step,
+        n_rows,
+        n_cols,
+        body: bytes[33..33 + body_len].to_vec(),
+    })
+}
+
+#[derive(Debug)]
+pub struct Decoded {
+    pub band_mhz: u32,
+    pub valid_time: DateTime<Utc>,
+    pub lat_min: f32,
+    pub lon_min: f32,
+    pub step: f32,
+    pub n_rows: u16,
+    pub n_cols: u16,
+    pub body: Vec<u8>,
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+    use chrono::TimeZone;
+
+    #[test]
+    fn round_trip_header() {
+        let scores = vec![ScorePoint {
+            lat: 32.0,
+            lon: -97.0,
+            score: 73,
+        }];
+        let ts = Utc.with_ymd_and_hms(2026, 4, 19, 15, 0, 0).unwrap();
+        let bytes = encode(10_000, ts, &scores).unwrap();
+        let decoded = decode(&bytes).unwrap();
+        assert_eq!(decoded.band_mhz, 10_000);
+        assert_eq!(decoded.valid_time, ts);
+        assert_eq!(decoded.n_rows, 201);
+        assert_eq!(decoded.n_cols, 473);
+        // Score at (32, -97): row = (32-25)/0.125 = 56, col = (-97 - -125)/0.125 = 224
+        let idx = 56 * 473 + 224;
+        assert_eq!(decoded.body[idx], 73);
+    }
+
+    #[test]
+    fn missing_cells_use_no_data_sentinel() {
+        let scores: Vec<ScorePoint> = vec![];
+        let ts = Utc.with_ymd_and_hms(2026, 4, 19, 15, 0, 0).unwrap();
+        let bytes = encode(10_000, ts, &scores).unwrap();
+        let decoded = decode(&bytes).unwrap();
+        assert!(decoded.body.iter().all(|&b| b == NO_DATA));
+    }
+
+    #[test]
+    fn clamps_out_of_range_scores() {
+        let scores = vec![
+            ScorePoint { lat: 25.0, lon: -125.0, score: -5 },
+            ScorePoint { lat: 25.125, lon: -125.0, score: 150 },
+        ];
+        let ts = Utc.with_ymd_and_hms(2026, 4, 19, 15, 0, 0).unwrap();
+        let bytes = encode(10_000, ts, &scores).unwrap();
+        let decoded = decode(&bytes).unwrap();
+        assert_eq!(decoded.body[0], 0);
+        // row = 1, col = 0 → idx = 1 * 473
+        assert_eq!(decoded.body[473], 100);
+    }
+
+    #[test]
+    fn path_for_layout() {
+        let ts = Utc.with_ymd_and_hms(2026, 4, 19, 15, 0, 0).unwrap();
+        let p = path_for(Path::new("/data/scores"), 10_000, ts);
+        assert_eq!(
+            p.to_str().unwrap(),
+            "/data/scores/10000/2026-04-19T15:00:00Z.ntms"
+        );
+    }
+
+    #[test]
+    fn atomic_write_and_decode() {
+        let dir = tempfile::tempdir().unwrap();
+        let ts = Utc.with_ymd_and_hms(2026, 4, 19, 15, 0, 0).unwrap();
+        let scores = vec![ScorePoint { lat: 32.0, lon: -97.0, score: 73 }];
+
+        write_atomic(dir.path(), 10_000, ts, &scores).unwrap();
+
+        let path = path_for(dir.path(), 10_000, ts);
+        let bytes = std::fs::read(&path).unwrap();
+        let decoded = decode(&bytes).unwrap();
+        assert_eq!(decoded.band_mhz, 10_000);
+        assert_eq!(decoded.body[56 * 473 + 224], 73);
+    }
+}

rust/prop_grid_rs/src/sounding_params.rs

@@ -0,0 +1,125 @@
+//! Minimum-refractivity-gradient derivation from pressure-level
+//! profiles. 1:1 port of the subset of
+//! `lib/microwaveprop/weather/sounding_params.ex` needed by the
+//! propagation grid scorer: `min_refractivity_gradient` per cell.
+//!
+//! The full Elixir module derives CAPE/LI/K-index/ducts — those are
+//! used for contact enrichment and f00's native-duct merge, neither of
+//! which is in the Rust f01..f18 scope.
+
+#[derive(Debug, Clone)]
+pub struct Level {
+    pub pres_mb: f64,
+    pub hght_m: f64,
+    pub tmpc: f64,
+    pub dwpc: Option<f64>,
+}
+
+/// Buck equation for saturation vapor pressure (hPa) at temperature in °C.
+pub fn sat_vap_pres(t_c: f64) -> f64 {
+    6.1121 * ((18.678 - t_c / 234.5) * (t_c / (257.14 + t_c))).exp()
+}
+
+/// Minimum refractivity gradient (dN/dh, N-units per km) from a pressure
+/// profile. Returns `None` if fewer than 3 usable levels or adjacent
+/// pairs too close in height. Levels are internally sorted descending by
+/// pressure (surface first) to match the Elixir orientation.
+pub fn min_refractivity_gradient(mut levels: Vec<Level>) -> Option<f64> {
+    levels.retain(|l| l.dwpc.is_some());
+    if levels.len() < 3 {
+        return None;
+    }
+    levels.sort_by(|a, b| {
+        b.pres_mb
+            .partial_cmp(&a.pres_mb)
+            .unwrap_or(std::cmp::Ordering::Equal)
+    });
+    let sfc_hght = levels[0].hght_m;
+
+    let refract: Vec<(f64, f64)> = levels
+        .iter()
+        .map(|l| {
+            let t_k = l.tmpc + 273.15;
+            let e = sat_vap_pres(l.dwpc.expect("filtered above"));
+            let n = 77.6 * l.pres_mb / t_k + 3.73e5 * e / (t_k * t_k);
+            let h_agl = l.hght_m - sfc_hght;
+            (h_agl, n)
+        })
+        .collect();
+
+    let mut min_grad: Option<f64> = None;
+    for pair in refract.windows(2) {
+        let (h0, n0) = pair[0];
+        let (h1, n1) = pair[1];
+        let dh_km = (h1 - h0) / 1000.0;
+        if dh_km.abs() < 0.01 {
+            continue;
+        }
+        let g = (n1 - n0) / dh_km;
+        min_grad = Some(match min_grad {
+            Some(prev) if prev <= g => prev,
+            _ => g,
+        });
+    }
+    min_grad
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn buck_sat_vap_at_freezing() {
+        // At 0 °C, Buck gives ~6.112 hPa.
+        let e = sat_vap_pres(0.0);
+        assert!((e - 6.112).abs() < 0.02, "{e}");
+    }
+
+    #[test]
+    fn nil_for_too_few_levels() {
+        let levels = vec![Level {
+            pres_mb: 1000.0,
+            hght_m: 0.0,
+            tmpc: 25.0,
+            dwpc: Some(20.0),
+        }];
+        assert!(min_refractivity_gradient(levels).is_none());
+    }
+
+    #[test]
+    fn typical_tropospheric_gradient_is_negative() {
+        // Synthetic profile: refractivity decreases with altitude → negative
+        // dN/dh. Realistic numbers from a standard atmosphere.
+        let levels = vec![
+            Level { pres_mb: 1000.0, hght_m: 100.0, tmpc: 25.0, dwpc: Some(20.0) },
+            Level { pres_mb: 925.0, hght_m: 800.0, tmpc: 20.0, dwpc: Some(14.0) },
+            Level { pres_mb: 850.0, hght_m: 1500.0, tmpc: 15.0, dwpc: Some(8.0) },
+            Level { pres_mb: 700.0, hght_m: 3000.0, tmpc: 5.0, dwpc: Some(-5.0) },
+        ];
+        let g = min_refractivity_gradient(levels).unwrap();
+        assert!(g < 0.0, "gradient should be negative: {g}");
+        assert!(g > -500.0, "no duct expected: {g}");
+    }
+
+    #[test]
+    fn surface_temperature_inversion_yields_stronger_gradient() {
+        // Surface inversion: cold moist near the ground, warm dry above —
+        // strong negative refractivity gradient.
+        let inversion = vec![
+            Level { pres_mb: 1000.0, hght_m: 100.0, tmpc: 18.0, dwpc: Some(17.0) },
+            Level { pres_mb: 990.0, hght_m: 300.0, tmpc: 22.0, dwpc: Some(5.0) },
+            Level { pres_mb: 950.0, hght_m: 700.0, tmpc: 20.0, dwpc: Some(3.0) },
+            Level { pres_mb: 850.0, hght_m: 1500.0, tmpc: 15.0, dwpc: Some(0.0) },
+        ];
+        let strong = min_refractivity_gradient(inversion).unwrap();
+
+        let neutral = vec![
+            Level { pres_mb: 1000.0, hght_m: 100.0, tmpc: 25.0, dwpc: Some(18.0) },
+            Level { pres_mb: 925.0, hght_m: 800.0, tmpc: 20.0, dwpc: Some(14.0) },
+            Level { pres_mb: 850.0, hght_m: 1500.0, tmpc: 15.0, dwpc: Some(8.0) },
+        ];
+        let baseline = min_refractivity_gradient(neutral).unwrap();
+
+        assert!(strong < baseline, "inversion {strong} vs baseline {baseline}");
+    }
+}

rust/prop_grid_rs/tests/scorer_golden.rs

@@ -0,0 +1,84 @@
+//! Golden-fixture regression test for the Rust scorer.
+//!
+//! Reads `tests/scores.bincode` (produced by `mix rust.golden` from the
+//! Elixir scorer) and asserts every (conditions, band) → score tuple
+//! matches. Regenerate after any scorer or band_config change:
+//!
+//!     mix rust.golden
+//!     cp priv/rust_golden/scores.bincode rust/prop_grid_rs/tests/
+//!
+//! The format is documented in `lib/mix/tasks/rust.golden.ex`.
+
+use std::io::{Cursor, Read};
+
+use byteorder::{LittleEndian, ReadBytesExt};
+use prop_grid_rs::{band_config, scorer};
+
+fn opt(v: f64) -> Option<f64> {
+    if v.is_nan() {
+        None
+    } else {
+        Some(v)
+    }
+}
+
+fn read_f64(r: &mut Cursor<&[u8]>) -> f64 {
+    r.read_f64::<LittleEndian>().expect("f64")
+}
+
+fn read_u8(r: &mut Cursor<&[u8]>) -> u8 {
+    let mut buf = [0u8; 1];
+    r.read_exact(&mut buf).expect("u8");
+    buf[0]
+}
+
+#[test]
+fn matches_elixir_golden_fixture() {
+    let bytes = std::fs::read("tests/scores.bincode")
+        .expect("tests/scores.bincode — run `mix rust.golden` first");
+    let mut r = Cursor::new(bytes.as_slice());
+
+    let n = r.read_u32::<LittleEndian>().expect("n_samples");
+    assert!(n > 0, "empty fixture");
+
+    let mut mismatches: Vec<String> = Vec::new();
+    for i in 0..n {
+        let c = scorer::Conditions {
+            abs_humidity: read_f64(&mut r),
+            temp_f: read_f64(&mut r),
+            dewpoint_f: read_f64(&mut r),
+            wind_speed_kts: opt(read_f64(&mut r)),
+            sky_cover_pct: opt(read_f64(&mut r)),
+            utc_hour: read_u8(&mut r),
+            utc_minute: read_u8(&mut r),
+            month: read_u8(&mut r),
+            longitude: read_f64(&mut r),
+            latitude: opt(read_f64(&mut r)),
+            pressure_mb: opt(read_f64(&mut r)),
+            prev_pressure_mb: opt(read_f64(&mut r)),
+            rain_rate_mmhr: opt(read_f64(&mut r)),
+            min_refractivity_gradient: opt(read_f64(&mut r)),
+            bl_depth_m: opt(read_f64(&mut r)),
+            pwat_mm: opt(read_f64(&mut r)),
+            best_duct_band_ghz: opt(read_f64(&mut r)),
+            bulk_richardson: opt(read_f64(&mut r)),
+        };
+        let band_mhz = r.read_u32::<LittleEndian>().expect("band_mhz");
+        let expected = r.read_i32::<LittleEndian>().expect("expected_score");
+
+        let band = band_config::get(band_mhz).expect("band in config");
+        let got = scorer::composite_score(&c, band).score;
+        if got != expected {
+            mismatches.push(format!(
+                "sample {i} band {band_mhz}: elixir={expected} rust={got}"
+            ));
+        }
+    }
+
+    assert!(
+        mismatches.is_empty(),
+        "{n} samples checked, {} mismatches:\n{}",
+        mismatches.len(),
+        mismatches.join("\n")
+    );
+}

test/microwaveprop/propagation/grid_task_enqueuer_test.exs

@@ -0,0 +1,53 @@
+defmodule Microwaveprop.Propagation.GridTaskEnqueuerTest do
+  use Microwaveprop.DataCase, async: true
+
+  import Ecto.Query
+
+  alias Microwaveprop.Propagation.GridTaskEnqueuer
+  alias Microwaveprop.Repo
+
+  test "seeds one row per fh=1..18" do
+    run_time = ~U[2026-04-19 15:00:00Z]
+    assert {:ok, 18} = GridTaskEnqueuer.seed(run_time)
+
+    rows =
+      Repo.all(
+        from(g in "grid_tasks",
+          where: g.run_time == ^run_time,
+          select: %{forecast_hour: g.forecast_hour, status: g.status, valid_time: g.valid_time}
+        )
+      )
+
+    assert length(rows) == 18
+    assert rows |> Enum.map(& &1.forecast_hour) |> Enum.sort() == Enum.to_list(1..18)
+    assert Enum.all?(rows, &(&1.status == "queued"))
+
+    # Raw schemaless selects return NaiveDateTime; compare against the
+    # equivalent naive form.
+    expected_naive = DateTime.to_naive(run_time)
+
+    Enum.each(rows, fn r ->
+      expected = NaiveDateTime.add(expected_naive, r.forecast_hour * 3600, :second)
+      assert NaiveDateTime.compare(r.valid_time, expected) == :eq
+    end)
+  end
+
+  test "is idempotent: reseeding the same run_time inserts nothing" do
+    run_time = ~U[2026-04-19 16:00:00Z]
+    assert {:ok, 18} = GridTaskEnqueuer.seed(run_time)
+    assert {:ok, 0} = GridTaskEnqueuer.seed(run_time)
+
+    count = Repo.one(from(g in "grid_tasks", where: g.run_time == ^run_time, select: count()))
+
+    assert count == 18
+  end
+
+  test "never emits a row for fh=0 — Elixir keeps that chain step" do
+    run_time = ~U[2026-04-19 17:00:00Z]
+    assert {:ok, 18} = GridTaskEnqueuer.seed(run_time)
+
+    f0_count = Repo.one(from(g in "grid_tasks", where: g.run_time == ^run_time and g.forecast_hour == 0, select: count()))
+
+    assert f0_count == 0
+  end
+end