test: assertions the adversarial review found missing -- log lines, immediate saves, snapshot isolation, store and temp-file failures, bounded snippet, identical list (review F9)

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

internal/progress/tracker_test.go

@@ -260,12 +260,56 @@ func TestTracker_EveryTransitionIsLoggedByTheSameCall(t *testing.T) {
 	tr.Begin("audio", 0)
 	clk.tick(3 * time.Second)
 	tr.Done("audio")
+	tr.Begin("decide", 5)
+	clk.tick(2 * time.Second)
+	tr.FailRunning()
+	tr.Finish()
 
 	out := buf.String()
-	require.Contains(t, out, "step=audio")
+	for _, want := range []string{
-	require.Contains(t, out, "started")
+		`msg="job started"`,
-	require.Contains(t, out, "finished")
+		`msg="step started" step=audio`,
-	require.Contains(t, out, "elapsed=3s")
+		`msg="step finished" step=audio elapsed=3s`,
+		`msg="step started" step=decide total=5`,
+		`msg="step failed" step=decide elapsed=2s`,
+		`msg="job finished"`,
+	} {
+		require.Contains(t, out, want, "a transition with no log line is invisible to the operator")
+	}
+}
+
+func TestTracker_AKeyedFailIsSavedAtOnceNotOnTheNextTransition(t *testing.T) {
+	tr, sink, _, _ := newTracker(t)
+	tr.Start()
+	tr.Begin("audio", 0)
+	before := sink.saveCount()
+
+	tr.Fail("audio", errors.New("down"))
+
+	require.Equal(t, before+1, sink.saveCount(), "a soft-failed phase must show as failed on the page now")
+	require.Equal(t, domain.StepFailed, stateOf(sink.last(t), "audio"))
+}
+
+// retainingSink keeps the very slice it is handed, like a sink that queues it for later.
+type retainingSink struct{ got [][]domain.ProgressStep }
+
+func (r *retainingSink) SaveProgress(_ context.Context, steps []domain.ProgressStep, _ time.Time) error {
+	r.got = append(r.got, steps)
+	return nil
+}
+func (r *retainingSink) Beat(context.Context) error { return nil }
+
+func TestTracker_ASnapshotHandedToTheSinkIsNotChangedByLaterTransitions(t *testing.T) {
+	sink := &retainingSink{}
+	tr := progress.NewTracker(context.Background(), sink, slog.New(slog.NewTextHandler(&syncBuf{}, nil)), plan(),
+		progress.WithClock(newClock().now))
+	tr.Start()
+	first := sink.got[0]
+
+	tr.Begin("audio", 0)
+	tr.Done("audio")
+
+	require.Equal(t, domain.StepPending, first[0].State, "a sink that keeps a snapshot must not see it change under it")
 }
 
 func TestTracker_AdvanceIsLoggedAtMostOncePerMinute(t *testing.T) {