feat(v0.4): add ConfirmYN prompt helper

internal/session/prompt.go

@@ -0,0 +1,32 @@
+package session
+
+import (
+	"bufio"
+	"fmt"
+	"io"
+	"strings"
+)
+
+// ConfirmYN prints prompt to out, reads one line from in, and returns:
+//   - true for "y"/"yes" (case-insensitive)
+//   - false for "n"/"no" (case-insensitive)
+//   - defaultYes for empty input
+//   - !defaultYes for any other input (treat unrecognized as the
+//     opposite of the default, i.e., the safer choice given the default)
+func ConfirmYN(in io.Reader, out io.Writer, prompt string, defaultYes bool) bool {
+	fmt.Fprint(out, prompt)
+	reader := bufio.NewReader(in)
+	line, _ := reader.ReadString('\n')
+	answer := strings.TrimSpace(strings.ToLower(line))
+
+	if answer == "" {
+		return defaultYes
+	}
+	if answer == "y" || answer == "yes" {
+		return true
+	}
+	if answer == "n" || answer == "no" {
+		return false
+	}
+	return !defaultYes
+}

internal/session/prompt_test.go

@@ -0,0 +1,45 @@
+package session
+
+import (
+	"bytes"
+	"strings"
+	"testing"
+)
+
+func TestConfirmYNAccepts(t *testing.T) {
+	cases := []struct {
+		in   string
+		def  bool
+		want bool
+	}{
+		{"y\n", false, true},
+		{"Y\n", false, true},
+		{"yes\n", false, true},
+		{"YES\n", false, true},
+		{"n\n", false, false},
+		{"no\n", false, false},
+		{"\n", false, false},
+		{"\n", true, true},
+		{"garbage\n", true, false},
+		{"garbage\n", false, true},
+	}
+
+	for _, c := range cases {
+		in := strings.NewReader(c.in)
+		var out bytes.Buffer
+		got := ConfirmYN(in, &out, "prompt? ", c.def)
+		if got != c.want {
+			t.Errorf("ConfirmYN(%q, default=%v) = %v, want %v", c.in, c.def, got, c.want)
+		}
+	}
+}
+
+func TestConfirmYNPromptsUser(t *testing.T) {
+	in := strings.NewReader("y\n")
+	var out bytes.Buffer
+	ConfirmYN(in, &out, "really? [y/N] ", false)
+
+	if !strings.Contains(out.String(), "really?") {
+		t.Errorf("expected prompt in output, got %q", out.String())
+	}
+}