test(progress): the default save and heartbeat deadline is pinned, not only the override (#51)

Every earlier test passed WithSaveTimeout; the worker passes nothing, so the 5 s default
was the only production value and a flip to 0, 1ms or 1h stayed green. Found by the PR #58
review; each flip is now red.

Co-Authored-By: Claude Sonnet 5.5 <noreply@anthropic.com>

internal/progress/tracker_stall_test.go

@@ -96,3 +96,59 @@ func TestTracker_TheStillRunningLineIsNotHeldUpBehindAHungSave(t *testing.T) {
 
 	require.Eventually(t, func() bool { return strings.Contains(buf.String(), "still running") }, 3*time.Second, 5*time.Millisecond)
 }
+
+// deadlineSink records how long each write was given, and answers at once.
+type deadlineSink struct {
+	mu     sync.Mutex
+	saves  []time.Duration
+	beats  []time.Duration
+	noDLOK bool
+}
+
+func (d *deadlineSink) record(ctx context.Context, into *[]time.Duration) {
+	d.mu.Lock()
+	defer d.mu.Unlock()
+	dl, ok := ctx.Deadline()
+	if !ok {
+		d.noDLOK = true
+		return
+	}
+	*into = append(*into, time.Until(dl))
+}
+
+func (d *deadlineSink) SaveProgress(ctx context.Context, _ []domain.ProgressStep, _ time.Time) error {
+	d.record(ctx, &d.saves)
+	return nil
+}
+
+func (d *deadlineSink) Beat(ctx context.Context, _ time.Time) error {
+	d.record(ctx, &d.beats)
+	return nil
+}
+
+// The production value is the one the worker gets: it builds a Tracker without options.
+// A zero or tiny default would drop every write, a huge one would bound nothing.
+func TestTracker_TheDefaultSaveAndBeatDeadlineIsAFewSecondsAway(t *testing.T) {
+	sink := &deadlineSink{}
+	tr := progress.NewTracker(context.Background(), sink, slog.New(slog.NewTextHandler(&lockedBuf{}, nil)),
+		[]progress.Planned{{Key: "a", Label: "A"}})
+	ctx, cancel := context.WithCancel(context.Background())
+	defer cancel()
+	go tr.Heartbeat(ctx, 5*time.Millisecond, time.Hour)
+
+	tr.Begin("a", 0)
+	require.Eventually(t, func() bool {
+		sink.mu.Lock()
+		defer sink.mu.Unlock()
+		return len(sink.beats) > 0
+	}, 3*time.Second, 5*time.Millisecond)
+
+	sink.mu.Lock()
+	defer sink.mu.Unlock()
+	require.False(t, sink.noDLOK, "a write was given no deadline at all")
+	require.NotEmpty(t, sink.saves)
+	for _, d := range append(append([]time.Duration{}, sink.saves...), sink.beats...) {
+		require.Greater(t, d, time.Second, "the deadline is already (nearly) spent when the write starts")
+		require.LessOrEqual(t, d, 5*time.Second, "the default bound is 5 s")
+	}
+}