fix(weather): tolerate stale map_bounds from /map → /weather navigation

/map's PropagationMap hook pushes `map_bounds` on every moveend/zoomend.
When a user live-navigates from /map to /weather, an in-flight bounds
push can land on the new WeatherMapLive (the same LV channel survives
the navigation), and WeatherMapLive's `handle_event/3` had no clause
for it — the LV process crashed with FunctionClauseError, taking the
user's session down.

WeatherMapLive doesn't need viewport bounds — the /weather/cells HTTP
endpoint reads them off the URL the client builds — so the safe fix is
a no-op handler. Tested.

lib/microwaveprop_web/live/weather_map_live.ex

@@ -232,6 +232,14 @@ defmodule MicrowavepropWeb.WeatherMapLive do
     end
   end
 
+  # `/map`'s PropagationMap hook pushes `map_bounds` on moveend/zoomend.
+  # When a user navigates /map → /weather, an in-flight bounds push from
+  # the old hook can land on the new WeatherMapLive (LV reuses sockets
+  # across live navigation). WeatherMapLive doesn't need bounds — the
+  # /weather/cells HTTP endpoint computes them client-side — so swallow
+  # the event instead of crashing the LV process.
+  def handle_event("map_bounds", _params, socket), do: {:noreply, socket}
+
   def handle_event("point_detail", %{"lat" => lat, "lon" => lon}, socket) do
     detail =
       if socket.assigns.valid_time do

test/microwaveprop_web/live/weather_map_live_test.exs

@@ -319,4 +319,26 @@ defmodule MicrowavepropWeb.WeatherMapLiveTest do
       assert html =~ ~s(data-selected-layer=)
     end
   end
+
+  describe "stale client events" do
+    test "ignores `map_bounds` from a stale browser tab without crashing", %{conn: conn} do
+      # A user can navigate /map → /weather while the propagation map's
+      # JS hook still has a queued moveend → pushEvent("map_bounds", …)
+      # in flight. The WeatherMapLive doesn't need viewport bounds (it
+      # fetches /weather/cells over HTTP using the *client* viewport),
+      # but it MUST tolerate the rogue event instead of crashing the
+      # LV process.
+      {:ok, lv, _html} = live(conn, ~p"/weather")
+
+      bounds = %{
+        "south" => 32.57,
+        "north" => 33.62,
+        "west" => -97.37,
+        "east" => -95.76
+      }
+
+      html = render_hook(lv, "map_bounds", bounds)
+      assert is_binary(html)
+    end
+  end
 end