fix(cli): route interactive ui to stderr

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

pkg/cli/output.go

@@ -114,15 +114,15 @@ func Dim(msg string) {
 func Progress(verb string, current, total int, item ...string) {
 	msg := i18n.Progress(verb)
 	if len(item) > 0 && item[0] != "" {
-		fmt.Printf("\033[2K\r%s %d/%d %s", DimStyle.Render(msg), current, total, item[0])
+		fmt.Fprintf(os.Stderr, "\033[2K\r%s %d/%d %s", DimStyle.Render(msg), current, total, item[0])
 	} else {
-		fmt.Printf("\033[2K\r%s %d/%d", DimStyle.Render(msg), current, total)
+		fmt.Fprintf(os.Stderr, "\033[2K\r%s %d/%d", DimStyle.Render(msg), current, total)
 	}
 }
 
 // ProgressDone clears the progress line.
 func ProgressDone() {
-	fmt.Print("\033[2K\r")
+	fmt.Fprint(os.Stderr, "\033[2K\r")
 }
 
 // Label prints a "Label: value" line.

pkg/cli/prompt.go

@@ -35,9 +35,9 @@ func Prompt(label, defaultVal string) (string, error) {
 	label = compileGlyphs(label)
 	defaultVal = compileGlyphs(defaultVal)
 	if defaultVal != "" {
-		fmt.Printf("%s [%s]: ", label, defaultVal)
+		fmt.Fprintf(os.Stderr, "%s [%s]: ", label, defaultVal)
 	} else {
-		fmt.Printf("%s: ", label)
+		fmt.Fprintf(os.Stderr, "%s: ", label)
 	}
 
 	r := newReader()
@@ -66,11 +66,11 @@ func Select(label string, options []string) (string, error) {
 		return "", nil
 	}
 
-	fmt.Println(compileGlyphs(label))
+	fmt.Fprintln(os.Stderr, compileGlyphs(label))
 	for i, opt := range options {
-		fmt.Printf("  %d. %s\n", i+1, compileGlyphs(opt))
+		fmt.Fprintf(os.Stderr, "  %d. %s\n", i+1, compileGlyphs(opt))
 	}
-	fmt.Printf("Choose [1-%d]: ", len(options))
+	fmt.Fprintf(os.Stderr, "Choose [1-%d]: ", len(options))
 
 	r := newReader()
 	input, err := r.ReadString('\n')
@@ -94,11 +94,11 @@ func MultiSelect(label string, options []string) ([]string, error) {
 		return []string{}, nil
 	}
 
-	fmt.Println(compileGlyphs(label))
+	fmt.Fprintln(os.Stderr, compileGlyphs(label))
 	for i, opt := range options {
-		fmt.Printf("  %d. %s\n", i+1, compileGlyphs(opt))
+		fmt.Fprintf(os.Stderr, "  %d. %s\n", i+1, compileGlyphs(opt))
 	}
-	fmt.Printf("Choose (space-separated) [1-%d]: ", len(options))
+	fmt.Fprintf(os.Stderr, "Choose (space-separated) [1-%d]: ", len(options))
 
 	r := newReader()
 	input, err := r.ReadString('\n')

pkg/cli/prompt_test.go

@@ -38,6 +38,49 @@ func captureStderr(t *testing.T, fn func()) string {
 	return buf.String()
 }
 
+func captureStdoutStderr(t *testing.T, fn func()) (string, string) {
+	t.Helper()
+
+	oldOut := os.Stdout
+	oldErr := os.Stderr
+	rOut, wOut, err := os.Pipe()
+	if !assert.NoError(t, err) {
+		return "", ""
+	}
+	rErr, wErr, err := os.Pipe()
+	if !assert.NoError(t, err) {
+		return "", ""
+	}
+	os.Stdout = wOut
+	os.Stderr = wErr
+
+	defer func() {
+		os.Stdout = oldOut
+		os.Stderr = oldErr
+	}()
+
+	fn()
+
+	if !assert.NoError(t, wOut.Close()) {
+		return "", ""
+	}
+	if !assert.NoError(t, wErr.Close()) {
+		return "", ""
+	}
+
+	var outBuf bytes.Buffer
+	var errBuf bytes.Buffer
+	_, err = io.Copy(&outBuf, rOut)
+	if !assert.NoError(t, err) {
+		return "", ""
+	}
+	_, err = io.Copy(&errBuf, rErr)
+	if !assert.NoError(t, err) {
+		return "", ""
+	}
+	return outBuf.String(), errBuf.String()
+}
+
 func TestPrompt_Good(t *testing.T) {
 	SetStdin(strings.NewReader("hello\n"))
 	defer SetStdin(nil) // reset
@@ -353,3 +396,17 @@ func TestPromptHints_Good_UseStderr(t *testing.T) {
 	assert.Contains(t, stderr.String(), "try again")
 	assert.Contains(t, stderr.String(), "invalid")
 }
+
+func TestPrompt_Good_WritesToStderr(t *testing.T) {
+	SetStdin(strings.NewReader("hello\n"))
+	defer SetStdin(nil)
+
+	stdout, stderr := captureStdoutStderr(t, func() {
+		val, err := Prompt("Name", "")
+		assert.NoError(t, err)
+		assert.Equal(t, "hello", val)
+	})
+
+	assert.Empty(t, stdout)
+	assert.Contains(t, stderr, "Name:")
+}

pkg/cli/tracker.go

@@ -114,7 +114,7 @@ func (tr *TaskTracker) Snapshots() iter.Seq2[string, string] {
 
 // NewTaskTracker creates a new parallel task tracker.
 func NewTaskTracker() *TaskTracker {
-	return &TaskTracker{out: os.Stdout}
+	return &TaskTracker{out: os.Stderr}
 }
 
 // Add registers a task and returns it for goroutine use.

pkg/cli/utils.go

@@ -110,7 +110,7 @@ func Confirm(prompt string, opts ...ConfirmOption) bool {
 	reader := newReader()
 
 	for {
-		fmt.Printf("%s %s", prompt, suffix)
+		fmt.Fprintf(os.Stderr, "%s %s", prompt, suffix)
 
 		var response string
 		var readErr error
@@ -130,7 +130,7 @@ func Confirm(prompt string, opts ...ConfirmOption) bool {
 				readErr = <-errChan
 				response = strings.ToLower(strings.TrimSpace(response))
 			case <-time.After(cfg.timeout):
-				fmt.Println() // New line after timeout
+				fmt.Fprintln(os.Stderr) // New line after timeout
 				return cfg.defaultYes
 			}
 		} else {
@@ -245,9 +245,9 @@ func Question(prompt string, opts ...QuestionOption) string {
 	for {
 		// Build prompt with default
 		if cfg.defaultValue != "" {
-			fmt.Printf("%s [%s] ", prompt, compileGlyphs(cfg.defaultValue))
+			fmt.Fprintf(os.Stderr, "%s [%s] ", prompt, compileGlyphs(cfg.defaultValue))
 		} else {
-			fmt.Printf("%s ", prompt)
+			fmt.Fprintf(os.Stderr, "%s ", prompt)
 		}
 
 		response, err := reader.ReadString('\n')
@@ -364,9 +364,9 @@ func Choose[T any](prompt string, items []T, opts ...ChooseOption[T]) T {
 		renderChoices(prompt, items, visible, cfg.displayFn, cfg.defaultN, cfg.filter)
 
 		if cfg.filter {
-			fmt.Printf("Enter number [1-%d] or filter: ", len(visible))
+			fmt.Fprintf(os.Stderr, "Enter number [1-%d] or filter: ", len(visible))
 		} else {
-			fmt.Printf("Enter number [1-%d]: ", len(visible))
+			fmt.Fprintf(os.Stderr, "Enter number [1-%d]: ", len(visible))
 		}
 		response, err := reader.ReadString('\n')
 		response = strings.TrimSpace(response)
@@ -458,9 +458,9 @@ func ChooseMulti[T any](prompt string, items []T, opts ...ChooseOption[T]) []T {
 		renderChoices(prompt, items, visible, cfg.displayFn, -1, cfg.filter)
 
 		if cfg.filter {
-			fmt.Printf("Enter numbers (e.g., 1 3 5 or 1-3), or filter text, or empty for none: ")
+			fmt.Fprint(os.Stderr, "Enter numbers (e.g., 1 3 5 or 1-3), or filter text, or empty for none: ")
 		} else {
-			fmt.Printf("Enter numbers (e.g., 1 3 5 or 1-3) or empty for none: ")
+			fmt.Fprint(os.Stderr, "Enter numbers (e.g., 1 3 5 or 1-3) or empty for none: ")
 		}
 		response, _ := reader.ReadString('\n')
 		response = strings.TrimSpace(response)
@@ -503,16 +503,16 @@ func ChooseMulti[T any](prompt string, items []T, opts ...ChooseOption[T]) []T {
 }
 
 func renderChoices[T any](prompt string, items []T, visible []int, displayFn func(T) string, defaultN int, filter bool) {
-	fmt.Println(prompt)
+	fmt.Fprintln(os.Stderr, prompt)
 	for i, idx := range visible {
 		marker := " "
 		if defaultN >= 0 && idx == defaultN {
 			marker = "*"
 		}
-		fmt.Printf("  %s%d. %s\n", marker, i+1, compileGlyphs(displayFn(items[idx])))
+		fmt.Fprintf(os.Stderr, "  %s%d. %s\n", marker, i+1, compileGlyphs(displayFn(items[idx])))
 	}
 	if filter {
-		fmt.Println("  (type to filter the list)")
+		fmt.Fprintln(os.Stderr, "  (type to filter the list)")
 	}
 }