fix(microprints): collapse expanded file when highlighting a different file

- Add test in microprints_live_test.exs that documents the uncoupled state bug
- Fix handle_event("highlight_line") to collapse expanded_path when
  highlighting a line in a different file
- All 159 tests pass

app/lib/firehose_web/live/microprints_live.ex

@@ -105,10 +105,18 @@ defmodule FirehoseWeb.MicroprintsLive do
         _ -> String.to_integer(line)
       end
 
+    # Collapse any currently expanded file when highlighting a different file
+    expanded =
+      case socket.assigns.expanded_path do
+        ^path -> socket.assigns.expanded_path
+        _ -> nil
+      end
+
     {:noreply,
      socket
      |> assign(:highlighted_path, path)
-     |> assign(:highlighted_line, highlighted)}
+     |> assign(:highlighted_line, highlighted)
+     |> assign(:expanded_path, expanded)}
   end
 
   @impl true

app/test/firehose_web/live/microprints_live_test.exs

@@ -1,5 +1,9 @@
+alias FirehoseWeb.MicroprintsLive
+
 defmodule FirehoseWeb.MicroprintsLiveTest do
-  use ExUnit.Case, async: true
+  use FirehoseWeb.ConnCase, async: true
+
+  import Phoenix.LiveViewTest
 
   describe "scan_source_files/0" do
     test "returns exactly 2 files" do
@@ -64,4 +68,36 @@ defmodule FirehoseWeb.MicroprintsLiveTest do
       assert is_list(blogex_files)
     end
   end
+
+  describe "expanded_path and highlighted_path coupling" do
+    test "expanding file A and highlighting a line in file B should collapse file A", %{conn: conn} do
+      files = MicroprintsLive.scan_source_files()
+      assert length(files) >= 2, "Need at least 2 files to test coupling"
+
+      [file_a, file_b | _] = files
+
+      {:ok, view, _html} = live(conn, ~p"/microprints")
+
+      # Expand file A
+      view
+      |> element("button[phx-value-path=\"#{file_a}\"]", "Expand")
+      |> render_click()
+
+      # Verify file A shows "Collapse" button (it's expanded)
+      html = render(view)
+      assert html =~ ~s(phx-value-path="#{file_a}")
+      assert html =~ "Collapse"
+
+      # Highlight a line in file B (rect elements inside SVG)
+      view
+      |> element("svg rect[phx-value-line=\"1\"][phx-value-path=\"#{file_b}\"]")
+      |> render_click()
+
+      # BUG: file A should be collapsed when highlighting a different file
+      # Currently file A stays expanded while the highlight is on file B
+      html = render(view)
+      refute html =~ "Collapse",
+             "file A should be collapsed after highlighting a different file, but the Collapse button is still visible (expanded_path is uncoupled from highlighted_path)"
+    end
+  end
 end