fix(bonfire): keep a blank line printed during a live view (IN-11, quick-261028-rqd)

modules/bonfire/live.go

@@ -539,8 +539,15 @@ func printAbove(owner *console, s string) bool {
 		return false
 	default:
 	}
+	block := strings.TrimSuffix(s, "\n")
+	if block == "" && s != "" {
+		// A blank line (Println()): bubbletea v2.1.0's insertAbove
+		// returns early for an empty string, which would drop it, so
+		// send a single space, which prints as a blank line.
+		block = " "
+	}
 	// One message for the whole block, sent while holding liveMu: blocks
 	// from different goroutines keep the order of their calls.
-	v.prog.Send(printLine(strings.TrimSuffix(s, "\n")))
+	v.prog.Send(printLine(block))
 	return true
 }

modules/bonfire/live_test.go

@@ -8,6 +8,7 @@ import (
 	"io"
 	"os"
 	"regexp"
+	"slices"
 	"strings"
 	"sync"
 	"testing"
@@ -712,3 +713,33 @@ func TestPrintAboveAfterCancel(t *testing.T) {
 		t.Error("a view is still registered after Process returned")
 	}
 }
+
+// insertedLine matches one line bubbletea v2 inserts above the view:
+// insert line (CSI L), the text, erase to the end of the line (CSI K).
+var insertedLine = regexp.MustCompile(`\x1b\[L(.*?)\x1b\[K`)
+
+// TestPrintAboveBlankLine (IN-11): a blank line printed during a live view
+// (out.Println()) prints a blank line above the view instead of being
+// dropped. bubbletea writes each line above the view as an inserted line,
+// so the test reads those insertions from the raw output: stripping the
+// escape sequences would also drop the cursor movement and show a blank
+// line that the terminal never gets.
+func TestPrintAboveBlankLine(t *testing.T) {
+	out := &lockedBuffer{}
+	c := newConsole(strings.NewReader(""), out, io.Discard, noEnv, boolPtr(true), boolPtr(true))
+	if err := c.Spinner("working", func() error {
+		c.Println("before-blank")
+		c.Println()
+		c.Println("after-blank")
+		return nil
+	}); err != nil {
+		t.Fatal(err)
+	}
+	var lines []string
+	for _, m := range insertedLine.FindAllStringSubmatch(out.String(), -1) {
+		lines = append(lines, strings.TrimSpace(ansi.Strip(m[1])))
+	}
+	if want := []string{"before-blank", "", "after-blank"}; !slices.Equal(lines, want) {
+		t.Errorf("lines inserted above the view = %q, want %q\nraw: %q", lines, want, out.String())
+	}
+}