fix(pager): fix pagers that use stdio

app/lib/linear_cli/cli/pager.ex

@@ -11,10 +11,9 @@ defmodule LinearCli.CLI.Pager do
   - The content's line count does not exceed the terminal's row count
 
   When paging is needed the content is written to a temp file and the
-  pager is invoked via `System.shell/1`, which — like
-  `Owl.IO.open_in_editor/2`'s own use of the same function — lets the
-  child process open `/dev/tty` directly for interactive keyboard
-  control.
+  The pager inherits the terminal's standard streams, so pagers that
+  render to standard output (such as `bat`) work as well as interactive
+  pagers such as `less`.
 
   ## Testing
 
@@ -38,12 +37,12 @@ defmodule LinearCli.CLI.Pager do
   - `:rows_fn` — 0-arity function returning terminal row count or `nil`
     (defaults to `&Owl.IO.rows/0`)
   - `:shell_fn` — 1-arity function receiving the full shell command
-    (defaults to `&System.shell/1`)
+    (defaults to a runner that inherits the terminal's standard streams)
   """
   @spec maybe_page(String.t(), map()) :: :ok
   def maybe_page(text, opts \\ %{}) do
     rows_fn = Map.get(opts, :rows_fn, &Owl.IO.rows/0)
-    shell_fn = Map.get(opts, :shell_fn, &System.shell/1)
+    shell_fn = Map.get(opts, :shell_fn, &run_pager/1)
     terminal_rows = rows_fn.()
     pager = resolve_pager()
 
@@ -87,6 +86,23 @@ defmodule LinearCli.CLI.Pager do
     :ok
   end
 
+  # `System.shell/1` captures a child's stdout. That made pagers such as
+  # `bat` appear to succeed while their output was silently discarded.
+  defp run_pager(command) do
+    shell = System.find_executable("sh") || raise "could not find sh on PATH"
+
+    port =
+      Port.open({:spawn_executable, shell}, [
+        :nouse_stdio,
+        :exit_status,
+        args: ["-c", command]
+      ])
+
+    receive do
+      {^port, {:exit_status, status}} -> {"", status}
+    end
+  end
+
   defp shell_quote(path) do
     "'" <> String.replace(path, "'", "'\\''") <> "'"
   end

app/test/linear_cli/cli/pager_test.exs

@@ -10,6 +10,18 @@ defmodule LinearCli.CLI.PagerTest do
   @long_text String.duplicate("line\n", 50)
   @short_text "just one line"
 
+  setup do
+    original = System.get_env("PAGER")
+    System.delete_env("PAGER")
+
+    on_exit(fn ->
+      case original do
+        nil -> System.delete_env("PAGER")
+        value -> System.put_env("PAGER", value)
+      end
+    end)
+  end
+
   describe "maybe_page/2 - not a TTY" do
     test "prints directly without invoking the pager" do
       {invoked, shell_fn} = spy_shell()