feat(websocket): add WebSocket display backend for browser client

tests/test_app.py

@@ -0,0 +1,55 @@
+"""
+Tests for engine.app module.
+"""
+
+from engine.app import _normalize_preview_rows
+
+
+class TestNormalizePreviewRows:
+    """Tests for _normalize_preview_rows function."""
+
+    def test_empty_rows(self):
+        """Empty input returns empty list."""
+        result = _normalize_preview_rows([])
+        assert result == [""]
+
+    def test_strips_left_padding(self):
+        """Left padding is stripped."""
+        result = _normalize_preview_rows(["  content", "  more"])
+        assert all(not r.startswith(" ") for r in result)
+
+    def test_preserves_content(self):
+        """Content is preserved."""
+        result = _normalize_preview_rows(["  hello world  "])
+        assert "hello world" in result[0]
+
+    def test_handles_all_empty_rows(self):
+        """All empty rows returns single empty string."""
+        result = _normalize_preview_rows(["", "   ", ""])
+        assert result == [""]
+
+
+class TestAppConstants:
+    """Tests for app module constants."""
+
+    def test_title_defined(self):
+        """TITLE is defined."""
+        from engine.app import TITLE
+
+        assert len(TITLE) > 0
+
+    def test_title_lines_are_strings(self):
+        """TITLE contains string lines."""
+        from engine.app import TITLE
+
+        assert all(isinstance(line, str) for line in TITLE)
+
+
+class TestAppImports:
+    """Tests for app module imports."""
+
+    def test_app_imports_without_error(self):
+        """Module imports without error."""
+        from engine import app
+
+        assert app is not None