diff --git a/lib/microwaveprop/propagation/scores_file.ex b/lib/microwaveprop/propagation/scores_file.ex
index 1a78ff39..1e232cc8 100644
--- a/lib/microwaveprop/propagation/scores_file.ex
+++ b/lib/microwaveprop/propagation/scores_file.ex
@@ -188,9 +188,14 @@ defmodule Microwaveprop.Propagation.ScoresFile do
 
     case File.ls(dir) do
       {:ok, files} ->
+        # Dedupe: during the `.ntms` → `.prop` rollout, both extensions
+        # can coexist for the same valid_time. `list_score_files` accepts
+        # either form, so without uniq the caller sees each forecast hour
+        # twice (visible as a duplicated chip in the map's timeline).
         files
         |> Enum.map(&parse_valid_time_dt/1)
         |> Enum.reject(&is_nil/1)
+        |> Enum.uniq()
         |> Enum.sort(DateTime)
 
       _ ->
diff --git a/lib/microwaveprop_web/live/contact_live/mechanism.ex b/lib/microwaveprop_web/live/contact_live/mechanism.ex
new file mode 100644
index 00000000..35a61138
--- /dev/null
+++ b/lib/microwaveprop_web/live/contact_live/mechanism.ex
@@ -0,0 +1,54 @@
+defmodule MicrowavepropWeb.ContactLive.Mechanism do
+  @moduledoc """
+  Display helpers for the propagation-mechanism badge shown on
+  `/contacts/:id`. The underlying classification lives in
+  `Microwaveprop.Propagation.MechanismClassifier`; this module just
+  translates the atom into a human label, a daisyUI badge class, and
+  a one-line explainer.
+
+  Extracted from the `ContactLive.Show` module as part of the
+  2026-04 cleanup — pure functions with no LiveView coupling belong
+  in their own file so the view itself shrinks toward render logic.
+  """
+
+  @type mechanism ::
+          :likely_rainscatter
+          | :rainscatter_possible
+          | :tropo_duct
+          | :troposcatter
+          | :unknown
+          | nil
+
+  @spec label(mechanism()) :: String.t()
+  def label(:likely_rainscatter), do: "Likely Rain Scatter"
+  def label(:rainscatter_possible), do: "Rain Scatter Possible"
+  def label(:tropo_duct), do: "Tropospheric Duct"
+  def label(:troposcatter), do: "Troposcatter"
+  def label(:unknown), do: "Unclassified"
+  def label(_), do: "Analyzing…"
+
+  @spec badge_class(mechanism()) :: String.t()
+  def badge_class(:likely_rainscatter), do: "badge-info"
+  def badge_class(:rainscatter_possible), do: "badge-info badge-outline"
+  def badge_class(:tropo_duct), do: "badge-warning"
+  def badge_class(:troposcatter), do: "badge-ghost"
+  def badge_class(:unknown), do: "badge-ghost"
+  def badge_class(_), do: "badge-ghost"
+
+  @spec explainer(mechanism()) :: String.t()
+  def explainer(:likely_rainscatter),
+    do:
+      "Heavy precipitation detected inside the common volume between the two stations — the most likely carrier at this frequency and distance."
+
+  def explainer(:rainscatter_possible),
+    do: "Light-to-moderate precipitation in the common volume, no ducting signature — scatter is plausible but marginal."
+
+  def explainer(:tropo_duct),
+    do: "HRRR profile shows a trapping layer (refractivity gradient below −157 N/km) at one of the endpoints."
+
+  def explainer(:troposcatter),
+    do: "No duct, no meaningful rain inside the common volume — default tropospheric forward scatter."
+
+  def explainer(:unknown), do: "Not enough radar/profile coverage to distinguish mechanisms."
+  def explainer(_), do: ""
+end
diff --git a/lib/microwaveprop_web/live/contact_live/show.ex b/lib/microwaveprop_web/live/contact_live/show.ex
index eebad038..633e6b00 100644
--- a/lib/microwaveprop_web/live/contact_live/show.ex
+++ b/lib/microwaveprop_web/live/contact_live/show.ex
@@ -19,6 +19,7 @@ defmodule MicrowavepropWeb.ContactLive.Show do
   alias Microwaveprop.Workers.NarrFetchWorker
   alias Microwaveprop.Workers.SolarIndexWorker
   alias Microwaveprop.Workers.TerrainProfileWorker
+  alias MicrowavepropWeb.ContactLive.Mechanism
 
   require Logger
 
@@ -1140,10 +1141,10 @@ defmodule MicrowavepropWeb.ContactLive.Show do
       <h2 class="text-base font-semibold mb-2">Propagation Mechanism</h2>
       <div class="mb-6 border border-base-300 rounded-lg p-4 text-sm">
         <div class="flex items-center gap-3 flex-wrap">
-          <span class={["badge badge-sm", mechanism_badge_class(@mechanism)]}>
-            {mechanism_label(@mechanism)}
+          <span class={["badge badge-sm", Mechanism.badge_class(@mechanism)]}>
+            {Mechanism.label(@mechanism)}
           </span>
-          <span class="opacity-70">{mechanism_explainer(@mechanism)}</span>
+          <span class="opacity-70">{Mechanism.explainer(@mechanism)}</span>
         </div>
         <%= if @radar do %>
           <div class="mt-3 flex flex-wrap gap-4 text-xs opacity-80">
@@ -1674,36 +1675,9 @@ defmodule MicrowavepropWeb.ContactLive.Show do
 
   defp format_number(n, _), do: to_string(n)
 
-  defp mechanism_label(:likely_rainscatter), do: "Likely Rain Scatter"
-  defp mechanism_label(:rainscatter_possible), do: "Rain Scatter Possible"
-  defp mechanism_label(:tropo_duct), do: "Tropospheric Duct"
-  defp mechanism_label(:troposcatter), do: "Troposcatter"
-  defp mechanism_label(:unknown), do: "Unclassified"
-  defp mechanism_label(_), do: "Analyzing…"
-
-  defp mechanism_badge_class(:likely_rainscatter), do: "badge-info"
-  defp mechanism_badge_class(:rainscatter_possible), do: "badge-info badge-outline"
-  defp mechanism_badge_class(:tropo_duct), do: "badge-warning"
-  defp mechanism_badge_class(:troposcatter), do: "badge-ghost"
-  defp mechanism_badge_class(:unknown), do: "badge-ghost"
-  defp mechanism_badge_class(_), do: "badge-ghost"
-
-  defp mechanism_explainer(:likely_rainscatter),
-    do:
-      "Heavy precipitation detected inside the common volume between the two stations — the most likely carrier at this frequency and distance."
-
-  defp mechanism_explainer(:rainscatter_possible),
-    do: "Light-to-moderate precipitation in the common volume, no ducting signature — scatter is plausible but marginal."
-
-  defp mechanism_explainer(:tropo_duct),
-    do: "HRRR profile shows a trapping layer (refractivity gradient below −157 N/km) at one of the endpoints."
-
-  defp mechanism_explainer(:troposcatter),
-    do: "No duct, no meaningful rain inside the common volume — default tropospheric forward scatter."
-
-  defp mechanism_explainer(:unknown), do: "Not enough radar/profile coverage to distinguish mechanisms."
-
-  defp mechanism_explainer(_), do: ""
+  # mechanism_label/1, mechanism_badge_class/1, mechanism_explainer/1
+  # live in MicrowavepropWeb.ContactLive.Mechanism (pure helpers, no
+  # LiveView coupling). Call via Mechanism.label/1 etc. in render.
 
   defp wind_speed_from_components(u, v) when is_number(u) and is_number(v) do
     mps = :math.sqrt(u * u + v * v)
diff --git a/test/microwaveprop/propagation/scores_file_test.exs b/test/microwaveprop/propagation/scores_file_test.exs
index 564dbd64..309b4552 100644
--- a/test/microwaveprop/propagation/scores_file_test.exs
+++ b/test/microwaveprop/propagation/scores_file_test.exs
@@ -192,6 +192,21 @@ defmodule Microwaveprop.Propagation.ScoresFileTest do
     test "returns an empty list when the band dir doesn't exist" do
       assert ScoresFile.list_valid_times(75_000) == []
     end
+
+    test "dedupes when a valid_time exists as both `.prop` and `.ntms`" do
+      # Simulate the rolling rename window: the new writer just dropped a
+      # .prop file; the prior cycle's .ntms file for the same valid_time
+      # is still on NFS. A naive implementation surfaces both → the /map
+      # timeline renders the same chip twice.
+      valid_time = ~U[2026-04-21 22:00:00Z]
+      ScoresFile.write!(10_000, valid_time, [])
+
+      base = Application.fetch_env!(:microwaveprop, :propagation_scores_dir)
+      legacy = Path.join([base, "10000", "2026-04-21T22-00-00Z.ntms"])
+      :ok = File.cp!(ScoresFile.path_for(10_000, valid_time), legacy)
+
+      assert ScoresFile.list_valid_times(10_000) == [valid_time]
+    end
   end
 
   describe "latest_valid_time/0" do