diff --git a/internal/session/run_integration_test.go b/internal/session/run_integration_test.go
new file mode 100644
index 0000000..80db557
--- /dev/null
+++ b/internal/session/run_integration_test.go
@@ -0,0 +1,76 @@
+package session
+
+import (
+	"errors"
+	"os"
+	"path/filepath"
+	"testing"
+	"time"
+)
+
+func TestFinalizeWritesSummaryAndClearsLease(t *testing.T) {
+	wsDir := t.TempDir()
+	os.MkdirAll(filepath.Join(wsDir, ".ctask"), 0755)
+
+	start := time.Now().UTC().Truncate(time.Second)
+	lease := NewLease(start, "claude", "local")
+	WriteLease(LeasePath(wsDir), lease)
+
+	os.WriteFile(filepath.Join(wsDir, "notes.md"), []byte("before"), 0644)
+	startManifest, err := CaptureManifest(wsDir)
+	if err != nil {
+		t.Fatalf("CaptureManifest: %v", err)
+	}
+	if err := WriteManifest(manifestStartPath(wsDir), startManifest); err != nil {
+		t.Fatalf("WriteManifest: %v", err)
+	}
+
+	time.Sleep(1 * time.Second)
+	os.WriteFile(filepath.Join(wsDir, "notes.md"), []byte("after change"), 0644)
+	os.WriteFile(filepath.Join(wsDir, "output.md"), []byte("new"), 0644)
+
+	end := time.Now().UTC().Truncate(time.Second)
+	opts := LaunchOpts{
+		WsDir: wsDir,
+		Agent: "claude",
+		Mode:  "local",
+		Slug:  "test",
+	}
+
+	if err := finalize(opts, startManifest, start, end, true); err != nil {
+		t.Fatalf("finalize: %v", err)
+	}
+
+	summary, err := ReadSummary(SummaryPath(wsDir))
+	if err != nil {
+		t.Fatalf("ReadSummary: %v", err)
+	}
+	if summary == nil {
+		t.Fatal("expected summary to be written")
+	}
+	if len(summary.FilesAdded) == 0 {
+		t.Error("expected files_added to contain output.md")
+	}
+	if len(summary.FilesModified) == 0 {
+		t.Error("expected files_modified to contain notes.md")
+	}
+	if len(summary.EndManifest) < 2 {
+		t.Errorf("expected end_manifest to include notes.md + output.md, got %d entries", len(summary.EndManifest))
+	}
+
+	logData, err := os.ReadFile(filepath.Join(wsDir, "logs", "sessions.log"))
+	if err != nil {
+		t.Fatalf("read session log: %v", err)
+	}
+	if len(logData) == 0 {
+		t.Error("session log should have content")
+	}
+
+	if _, err := os.Stat(LeasePath(wsDir)); !errors.Is(err, os.ErrNotExist) {
+		t.Errorf("lease should be removed after finalize, got err=%v", err)
+	}
+
+	if _, err := os.Stat(manifestStartPath(wsDir)); !errors.Is(err, os.ErrNotExist) {
+		t.Errorf("manifest-start should be removed after finalize, got err=%v", err)
+	}
+}