fix(ci): correct print callback arity in AdoCli.CI.Watcher

Bug: the default :print_callback was \&IO.write/2 (a 2-arity
function expecting device + data), but every render function
called it as `print.(line)` (1-arity). On first status
update, this raised:

  (BadArityError) &IO.write/2 with arity 2 called with 1 argument
    ("? Build 9655 · status=inProgress result=nil · <1s\n")
      (ado_cli 0.2.2) lib/ado_cli/ci/watcher.ex:124: render_status/3

So every invocation of `ado ci watch` crashed on the first
poll, before it could ever print a single status line.

Fix: change the default to a 1-arity wrapper:
  &IO.write(:stdio, &1)

Also made render_status/3 and render_final/2 public (`def`
instead of `defp`) so they can be unit-tested directly.
Added a regression test that exercises render_status/3 with a
1-arity print collector and asserts the printed output. This
test would have failed (BadArityError) on the broken version.

315 tests pass, mix ci 8/8 green, reach still 1 finding in
our code (logout behaviour candidate, false positive).

Author: gilbertwong96

lib/ado_cli/ci/watcher.ex

@@ -37,14 +37,14 @@ defmodule AdoCli.CI.Watcher do
   ## Options
 
     * `:poll_ms` — how often to poll (default 2000ms, min 250ms)
-    * `:print_callback` — function for output (default: &IO.write/2).
-      Tests inject a collector here.
+    * `:print_callback` — 1-arity function for output (default:
+      `&IO.write(:stdio, &1)`). Tests inject a collector here.
   """
   @spec watch(integer(), String.t(), String.t() | nil, keyword()) ::
           :ok | {:error, term()}
   def watch(build_id, project, org, opts \\ []) do
     poll_ms = max(Keyword.get(opts, :poll_ms, 2000), 250)
-    print = Keyword.get(opts, :print_callback, &IO.write/2)
+    print = Keyword.get(opts, :print_callback, &IO.write(:stdio, &1))
 
     state = %{
       build_id: build_id,
@@ -99,7 +99,9 @@ defmodule AdoCli.CI.Watcher do
 
   # ── status rendering ────────────────────────────────────────────────
 
-  defp render_status(build, started_at, print) do
+  # Public for unit testing. Not part of the user-facing API; the
+  # only caller is the watcher loop in this module.
+  def render_status(build, started_at, print) do
     elapsed_ms = System.monotonic_time(:millisecond) - started_at
     elapsed = format_duration(elapsed_ms)
 
@@ -124,7 +126,8 @@ defmodule AdoCli.CI.Watcher do
     print.(line <> "\n")
   end
 
-  defp render_final(build, print) do
+  # Public for unit testing. Not part of the user-facing API.
+  def render_final(build, print) do
     case build do
       %{"result" => "succeeded"} ->
         print.("\n  Build succeeded.\n")

test/ado_cli/ci/watcher_test.exs

@@ -38,6 +38,41 @@ defmodule AdoCli.CI.WatcherTest do
     end
   end
 
+  describe "render_status/3 (regression: BadArityError on print callback)" do
+    # In v0.2.1/v0.2.2 the default :print_callback was &IO.write/2
+    # (a 2-arity function), but render_status/3 calls it as
+    # `print.(line)` — 1-arity. That raised BadArityError on every
+    # status update. The fix changed the default to a 1-arity
+    # wrapper: `&IO.write(:stdio, &1)`.
+    #
+    # This test exercises render_status/3 directly with a simple
+    # 1-arity print collector and asserts the printed output. It
+    # would also have caught the original bug (it would have raised
+    # BadArityError at `print.(line)`).
+    test "prints status line via a 1-arity print callback" do
+      build = %{
+        "id" => 9655,
+        "status" => "inProgress",
+        "result" => nil,
+        "definition" => %{"name" => "my-pipeline"},
+        "sourceBranch" => "refs/heads/main"
+      }
+
+      parent = self()
+      print = fn line -> send(parent, {:printed, line}) end
+
+      started_at = System.monotonic_time(:millisecond)
+      Watcher.render_status(build, started_at, print)
+
+      assert_receive {:printed, line}, 500
+      assert line =~ "Build 9655"
+      assert line =~ "my-pipeline"
+      assert line =~ "refs/heads/main"
+      assert line =~ "running for"
+      assert line =~ "\n"
+    end
+  end
+
   describe "stream_log (with mock client)" do
     test "prints new log lines" do
       output = run_with_mocked_log(build_id: 123, log_id: 7, lines: ["line one", "line two"])