fix(cli): route stream output through injected stdout writer

Co-Authored-By: Virgil <virgil@lethean.io>

docs/pkg/cli/streaming.md

@@ -34,7 +34,8 @@ When word-wrap is enabled, the stream tracks the current column position and ins
 
 ## Custom Output Writer
 
-By default, streams write to `os.Stdout`. Redirect to any `io.Writer`:
+By default, streams write to the CLI stdout writer (`stdoutWriter()`), so tests can
+redirect output via `cli.SetStdout` and other callers can provide any `io.Writer`:
 
 ```go
 var buf strings.Builder
@@ -77,7 +78,7 @@ stream.Done()
 | Option | Description |
 |--------|-------------|
 | `WithWordWrap(cols)` | Set the word-wrap column width |
-| `WithStreamOutput(w)` | Set the output writer (default: `os.Stdout`) |
+| `WithStreamOutput(w)` | Set the output writer (default: `stdoutWriter()`) |
 
 ## Example: LLM Token Streaming
 

pkg/cli/stream.go

@@ -3,7 +3,6 @@ package cli
 import (
 	"fmt"
 	"io"
-	"os"
 	"strings"
 	"sync"
 
@@ -12,7 +11,8 @@ import (
 
 // StreamOption configures a Stream.
 //
-//	stream := cli.NewStream(cli.WithWordWrap(80), cli.WithStreamOutput(os.Stdout))
+//	stream := cli.NewStream(cli.WithWordWrap(80))
+//	stream.Wait()
 type StreamOption func(*Stream)
 
 // WithWordWrap sets the word-wrap column width.
@@ -20,7 +20,7 @@ func WithWordWrap(cols int) StreamOption {
 	return func(s *Stream) { s.wrap = cols }
 }
 
-// WithStreamOutput sets the output writer (default: os.Stdout).
+// WithStreamOutput sets the output writer (default: stdoutWriter()).
 func WithStreamOutput(w io.Writer) StreamOption {
 	return func(s *Stream) { s.out = w }
 }
@@ -48,7 +48,7 @@ type Stream struct {
 // NewStream creates a streaming text renderer.
 func NewStream(opts ...StreamOption) *Stream {
 	s := &Stream{
-		out:  os.Stdout,
+		out:  stdoutWriter(),
 		done: make(chan struct{}),
 	}
 	for _, opt := range opts {

pkg/cli/stream_test.go

@@ -10,6 +10,19 @@ import (
 )
 
 func TestStream_Good(t *testing.T) {
+	t.Run("uses injected stdout by default", func(t *testing.T) {
+		var buf bytes.Buffer
+		SetStdout(&buf)
+		defer SetStdout(nil)
+		s := NewStream()
+
+		s.Write("hello")
+		s.Done()
+		s.Wait()
+
+		assert.Equal(t, "hello\n", buf.String())
+	})
+
 	t.Run("basic write", func(t *testing.T) {
 		var buf bytes.Buffer
 		s := NewStream(WithStreamOutput(&buf))