Clear superseded session stage result details

internal/app/runner_test.go

@@ -742,6 +742,41 @@ func TestExecuteStagesForceRerunsSucceeded(t *testing.T) {
 	}
 }
 
+func TestExecuteStagesSuccessfulReplacementDoesNotInheritResultDetails(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))
+	existing.MarkStageSucceeded("transcribe", time.Date(2026, 5, 3, 1, 1, 0, 0, time.UTC), []manifest.ArtifactRecord{{
+		Kind: "transcript_raw", LocalPath: "transcripts/old.json",
+	}})
+	existingStage := existing.Stages["transcribe"]
+	existingStage.Logs = []string{"logs/old.log"}
+	existingStage.GeneratedConfigs = []string{"generated/old.yaml"}
+	existingStage.Metadata = map[string]any{"old_result": true}
+	if err := store.Save(context.Background(), manifestPath, existing); err != nil {
+		t.Fatalf("Save manifest error = %v", err)
+	}
+
+	runs := 0
+	replacement := resultStage{name: "transcribe", result: &stage.StageResult{}, runs: &runs}
+	if _, err := executeStages(context.Background(), cfg, []stage.Stage{replacement}, RunOptions{Force: true}); err != nil {
+		t.Fatalf("executeStages() error = %v", err)
+	}
+	loaded, err := store.Load(context.Background(), manifestPath)
+	if err != nil {
+		t.Fatalf("Load manifest error = %v", err)
+	}
+	record := loaded.Stages["transcribe"]
+	if runs != 1 || record == nil || record.Status != manifest.StatusSucceeded {
+		t.Fatalf("runs = %d, record = %#v, want one successful replacement", runs, record)
+	}
+	if len(record.Outputs) != 0 || len(record.Logs) != 0 || len(record.GeneratedConfigs) != 0 || len(record.Metadata) != 0 {
+		t.Fatalf("replacement inherited result details: %#v", record)
+	}
+}
+
 func TestExecuteStagesForceSuccessInvalidatesDownstreamSucceededStages(t *testing.T) {
 	cfg := testConfig(t)
 	manifestPath := manifestPathFor(cfg)