fix(import): return readable string for unreadable upload errors

File.read/1 only yields posix atoms, so the File.Error and bare-reason branches were unreachable, and :file.format_error/1 returns a charlist rather than a String. Normalize the error to a binary so it interpolates correctly in flash messages.

lib/mv/membership/import/import_runner.ex

@@ -26,14 +26,8 @@ defmodule Mv.Membership.Import.ImportRunner do
       {:ok, content} ->
         {:ok, content}
 
-      {:error, reason} when is_atom(reason) ->
-        {:error, :file.format_error(reason)}
-
-      {:error, %File.Error{reason: reason}} ->
-        {:error, :file.format_error(reason)}
-
       {:error, reason} ->
-        {:error, Exception.message(reason)}
+        {:error, to_string(:file.format_error(reason))}
     end
   end
 

test/mv/membership/import/import_runner_test.exs

@@ -0,0 +1,33 @@
+defmodule Mv.Membership.Import.ImportRunnerTest do
+  use ExUnit.Case, async: true
+
+  alias Mv.Membership.Import.ImportRunner
+
+  describe "read_file_entry/2" do
+    test "returns {:ok, content} for a readable file" do
+      path =
+        Path.join(
+          System.tmp_dir!(),
+          "import_runner_read_#{System.unique_integer([:positive])}.csv"
+        )
+
+      File.write!(path, "email;first_name\njohn@example.com;John")
+      on_exit(fn -> File.rm_rf(path) end)
+
+      assert {:ok, "email;first_name\njohn@example.com;John"} =
+               ImportRunner.read_file_entry(%{path: path}, %{})
+    end
+
+    test "returns {:error, message} with a binary message when the file cannot be read" do
+      missing_path =
+        Path.join(
+          System.tmp_dir!(),
+          "import_runner_missing_#{System.unique_integer([:positive])}.csv"
+        )
+
+      assert {:error, message} = ImportRunner.read_file_entry(%{path: missing_path}, %{})
+      assert is_binary(message)
+      assert message != ""
+    end
+  end
+end