fix(bonfire): reroute only the owning console's lines to a live view

- the registered view keeps the console that started it; Println, Printf
  and status lines go above it only from that console, other consoles
  write to their own writers (bonfire.PrintAbove still reaches any view)
- runLive claims the single live slot by check and set under liveMu and
  reports when it could not, so the widget prints plain lines
- unregister, finish and wait run deferred, so a panic in work leaves no
  registration behind and still propagates (WR-02)

modules/bonfire/live_test.go

@@ -427,3 +427,106 @@ func TestPrintAboveOrderedNoLoss(t *testing.T) {
 		}
 	})
 }
+
+// TestPrintlnStaysWithItsConsole (WR-02): while a view runs on console A,
+// another console's Println, Printf and Info go to its own writer; A's own
+// Println still prints above its view.
+func TestPrintlnStaysWithItsConsole(t *testing.T) {
+	bufA, bufB := &lockedBuffer{}, &lockedBuffer{}
+	a := newConsole(strings.NewReader(""), bufA, io.Discard, noEnv, boolPtr(true), boolPtr(true))
+	b := newConsole(strings.NewReader(""), bufB, bufB, noEnv, boolPtr(false), boolPtr(false))
+	err := a.Spinner("working", func() error {
+		b.Println("b-println")
+		b.Printf("b-printf %d\n", 1)
+		b.Info("b-info")
+		a.Println("a-println")
+		return nil
+	})
+	if err != nil {
+		t.Fatal(err)
+	}
+	gotA, gotB := ansi.Strip(bufA.String()), ansi.Strip(bufB.String())
+	for _, want := range []string{"b-println", "b-printf 1", "b-info"} {
+		if !strings.Contains(gotB, want) {
+			t.Errorf("console B's writer lacks %q:\n%s", want, gotB)
+		}
+		if strings.Contains(gotA, want) {
+			t.Errorf("console B's %q printed above console A's view:\n%s", want, gotA)
+		}
+	}
+	if !strings.Contains(gotA, "a-println") {
+		t.Errorf("console A's own line missing above its view:\n%s", gotA)
+	}
+}
+
+// TestLiveViewSingleOwner (WR-02): two consoles starting a spinner at the
+// same moment never both run a live view; the one that loses prints its
+// plain line to its own writer.
+func TestLiveViewSingleOwner(t *testing.T) {
+	const rounds = 200
+	for round := range rounds {
+		bufs := [2]*lockedBuffer{{}, {}}
+		var start, entered sync.WaitGroup
+		start.Add(1)
+		entered.Add(2)
+		var wg sync.WaitGroup
+		for i := range 2 {
+			wg.Add(1)
+			go func() {
+				defer wg.Done()
+				c := newConsole(strings.NewReader(""), bufs[i], io.Discard, noEnv, boolPtr(true), boolPtr(true))
+				start.Wait()
+				_ = c.Spinner(fmt.Sprintf("label-%d", i), func() error {
+					entered.Done()
+					entered.Wait() // both work functions run at once
+					return nil
+				})
+			}()
+		}
+		start.Done()
+		wg.Wait()
+		plain := 0
+		for i, b := range bufs {
+			if strings.Contains(ansi.Strip(b.String()), fmt.Sprintf("[...] label-%d", i)) {
+				plain++
+			}
+		}
+		if plain != 1 {
+			t.Fatalf("round %d: %d consoles printed their plain line to their own writer, want 1:\nA: %q\nB: %q",
+				round, plain, ansi.Strip(bufs[0].String()), ansi.Strip(bufs[1].String()))
+		}
+		if PrintAbove("after the round") {
+			t.Fatalf("round %d: a view is still registered", round)
+		}
+	}
+}
+
+// TestLiveViewPanicUnregisters (WR-02): a panic in the work function still
+// ends and unregisters the view; the next widget runs as a live view.
+func TestLiveViewPanicUnregisters(t *testing.T) {
+	out := &lockedBuffer{}
+	c := newConsole(strings.NewReader(""), out, io.Discard, noEnv, boolPtr(true), boolPtr(true))
+	func() {
+		defer func() {
+			if r := recover(); r != "boom" {
+				t.Fatalf("recovered %v, want the work function's panic", r)
+			}
+		}()
+		_ = c.Spinner("panicking", func() error { panic("boom") })
+	}()
+	if PrintAbove("after the panic") {
+		t.Fatal("the panicked view is still registered")
+	}
+	next := &lockedBuffer{}
+	c2 := newConsole(strings.NewReader(""), next, io.Discard, noEnv, boolPtr(true), boolPtr(true))
+	var during bool
+	if err := c2.Spinner("next", func() error {
+		during = PrintAbove("above the next view")
+		return nil
+	}); err != nil {
+		t.Fatal(err)
+	}
+	if !during || strings.Contains(ansi.Strip(next.String()), "[...] next") {
+		t.Errorf("the next spinner did not run as a live view:\n%s", ansi.Strip(next.String()))
+	}
+}