fix(rover-planning): edit-mode remove_station deletes only the targeted row

Clicking the trash icon on a stationary station in :edit mode before
any other phx-change had fired emptied the form's stations params,
which combined with cast_assoc(on_replace: :delete) wiped EVERY
existing station instead of just the one the user clicked. Fall back
to rebuilding the params from the persisted mission's stations when
the form's current params don't already carry them, then delete only
the targeted index.

lib/microwaveprop_web/live/rover_planning_live/form.ex

@@ -91,7 +91,7 @@ defmodule MicrowavepropWeb.RoverPlanningLive.Form do
 
   def handle_event("add_station", _params, socket) do
     params = current_params(socket)
-    stations = Map.get(params, "stations", %{})
+    stations = stations_params(socket, params)
     next_index = next_station_index(stations)
 
     # Don't include "input" in the new station's params — `used_input?/1`
@@ -113,8 +113,7 @@ defmodule MicrowavepropWeb.RoverPlanningLive.Form do
 
   def handle_event("remove_station", %{"index" => index}, socket) do
     params = current_params(socket)
-    stations = Map.get(params, "stations", %{})
-    stations = Map.delete(stations, index)
+    stations = socket |> stations_params(params) |> Map.delete(index)
 
     cs =
       socket.assigns.mission
@@ -124,6 +123,35 @@ defmodule MicrowavepropWeb.RoverPlanningLive.Form do
     {:noreply, assign(socket, form: to_form(cs))}
   end
 
+  # When the form changeset already carries a "stations" params map
+  # (every keystroke fires phx-change="validate" which builds one),
+  # trust it. Otherwise — e.g. the user clicked add/remove BEFORE
+  # touching any other input on an :edit-mode form — fall back to
+  # rebuilding the params from the persisted mission's stations so
+  # `cast_assoc(on_replace: :delete)` doesn't wipe every existing row.
+  defp stations_params(socket, %{"stations" => stations}) when is_map(stations) and stations != %{}, do: stations
+
+  defp stations_params(socket, _params), do: stations_from_mission(socket.assigns.mission)
+
+  defp stations_from_mission(%Mission{stations: list}) when is_list(list) do
+    list
+    |> Enum.with_index()
+    |> Map.new(fn {s, i} ->
+      {Integer.to_string(i),
+       %{
+         "id" => s.id,
+         "input" => s.input || s.callsign || s.grid,
+         "callsign" => s.callsign,
+         "grid" => s.grid,
+         "lat" => s.lat,
+         "lon" => s.lon,
+         "position" => Integer.to_string(s.position || i)
+       }}
+    end)
+  end
+
+  defp stations_from_mission(_), do: %{}
+
   def handle_event("save", %{"mission" => params}, socket) do
     user = socket.assigns.current_user
 

test/microwaveprop_web/live/rover_planning_live_test.exs

@@ -565,6 +565,41 @@ defmodule MicrowavepropWeb.RoverPlanningLiveTest do
                live(conn, ~p"/rover-planning/new")
     end
 
+    test "edit-mode remove_station deletes ONLY the targeted station", %{conn: conn} do
+      user = AccountsFixtures.user_fixture()
+      _loc = AccountsFixtures.user_fixture()
+
+      mission =
+        create_mission(user, "Multi-station edit",
+          stations: %{
+            "0" => %{"input" => "EM12kp", "position" => 0},
+            "1" => %{"input" => "EM13ks", "position" => 1},
+            "2" => %{"input" => "EM14lr", "position" => 2}
+          }
+        )
+
+      conn = log_in_user(conn, user)
+      {:ok, lv, _html} = live(conn, ~p"/rover-planning/#{mission.id}/edit")
+
+      # Click the trash icon on the second station (index 1) without
+      # any prior validate firing — this was the bug: an empty
+      # current_params + cast_assoc(on_replace: :delete) wiped every
+      # existing station instead of just the targeted index.
+      _html =
+        lv
+        |> element("button[phx-click='remove_station'][phx-value-index='1']")
+        |> render_click()
+
+      # Save and assert only stations 0 and 2 remain.
+      {:error, {:live_redirect, _}} =
+        lv
+        |> form("#mission-form")
+        |> render_submit()
+
+      reloaded = Repo.preload(Repo.get!(Microwaveprop.RoverPlanning.Mission, mission.id), :stations)
+      assert length(reloaded.stations) == 2
+    end
+
     test "clicking 'Add station' does not show 'can't be blank' on the new row", %{conn: conn} do
       user = AccountsFixtures.user_fixture()
       conn = log_in_user(conn, user)