Implement minimal downstream invalidation after forced upstream reruns

internal/app/runner_test.go

@@ -235,6 +235,56 @@ func TestExecuteStagesForceRerunsSucceeded(t *testing.T) {
 	}
 }
 
+func TestExecuteStagesForceSuccessInvalidatesDownstreamSucceededStages(t *testing.T) {
+	cfg := testConfig(t)
+	manifestPath := manifestPathFor(cfg)
+	store := &manifest.LocalStore{}
+
+	existing := manifest.New(cfg.Session.SessionID, time.Date(2026, 5, 3, 1, 0, 0, 0, time.UTC))
+	for _, stageName := range []string{"prepare", "transcribe", "merge", "polish", "normalize", "trim", "archive", "notify"} {
+		existing.MarkStageSucceeded(stageName, time.Date(2026, 5, 3, 1, 1, 0, 0, time.UTC), nil)
+	}
+	existing.MarkStageFailed("analyze", time.Date(2026, 5, 3, 1, 1, 0, 0, time.UTC), "previous analyze failure")
+	if err := os.MkdirAll(filepath.Dir(manifestPath), 0o755); err != nil {
+		t.Fatalf("MkdirAll() error = %v", err)
+	}
+	if err := store.Save(context.Background(), manifestPath, existing); err != nil {
+		t.Fatalf("Save manifest error = %v", err)
+	}
+
+	runs := 0
+	stageToRun := countingStage{name: "polish", runs: &runs}
+	summary, err := executeStages(context.Background(), cfg, []stage.Stage{stageToRun}, RunOptions{Force: true})
+	if err != nil {
+		t.Fatalf("executeStages() error = %v", err)
+	}
+	if runs != 1 {
+		t.Fatalf("runs = %d, want 1 with force", runs)
+	}
+	if len(summary.Executed) != 1 || summary.Executed[0] != "polish" || len(summary.Skipped) != 0 {
+		t.Fatalf("summary = %#v, want executed polish", summary)
+	}
+
+	loaded, err := store.Load(context.Background(), manifestPath)
+	if err != nil {
+		t.Fatalf("Load manifest error = %v", err)
+	}
+	if loaded.Stages["polish"] == nil || loaded.Stages["polish"].Status != manifest.StatusSucceeded {
+		t.Fatalf("polish status = %#v, want succeeded", loaded.Stages["polish"])
+	}
+	for _, stageName := range []string{"normalize", "trim", "archive", "notify"} {
+		if loaded.Stages[stageName] == nil || loaded.Stages[stageName].Status != manifest.StatusStale {
+			t.Fatalf("%s status = %#v, want stale", stageName, loaded.Stages[stageName])
+		}
+	}
+	if loaded.Stages["analyze"] == nil || loaded.Stages["analyze"].Status != manifest.StatusFailed {
+		t.Fatalf("analyze status = %#v, want preserved failed", loaded.Stages["analyze"])
+	}
+	if loaded.Stages["transcribe"] == nil || loaded.Stages["transcribe"].Status != manifest.StatusSucceeded {
+		t.Fatalf("transcribe status = %#v, want preserved succeeded", loaded.Stages["transcribe"])
+	}
+}
+
 func TestExecuteStagesFailureUpdatesManifest(t *testing.T) {
 	cfg := testConfig(t)