Validate demo root paths

src/telemetry_window_demo/cli.py

@@ -214,11 +214,11 @@ def plot_command(args: argparse.Namespace) -> None:
         print(f"     - {plot_path.name}")
 
 
-def run_ai_demo_command(args: argparse.Namespace) -> None:
-    from .ai_assisted_detection_demo import default_demo_root, run_demo
-
-    demo_root = Path(args.demo_root).resolve() if args.demo_root else default_demo_root()
-    result = run_demo(demo_root=demo_root)
+def run_ai_demo_command(args: argparse.Namespace) -> None:
+    from .ai_assisted_detection_demo import default_demo_root, run_demo
+
+    demo_root = _demo_root_path(args.demo_root, default_demo_root())
+    result = run_demo(demo_root=demo_root)
 
     print(f"[OK] Loaded {result['raw_event_count']} raw events")
     print(f"[OK] Normalized {result['normalized_event_count']} events")
@@ -235,8 +235,8 @@ def run_ai_demo_command(args: argparse.Namespace) -> None:
 def run_rule_dedup_demo_command(args: argparse.Namespace) -> None:
     from .rule_evaluation_and_dedup_demo import default_demo_root, run_demo
 
-    demo_root = Path(args.demo_root).resolve() if args.demo_root else default_demo_root()
-    result = run_demo(demo_root=demo_root)
+    demo_root = _demo_root_path(args.demo_root, default_demo_root())
+    result = run_demo(demo_root=demo_root)
 
     print(f"[OK] Loaded {result['raw_hit_count']} raw rule hits")
     print(f"[OK] Retained {result['retained_alert_count']} alerts")
@@ -250,7 +250,7 @@ def run_rule_dedup_demo_command(args: argparse.Namespace) -> None:
 def run_config_change_demo_command(args: argparse.Namespace) -> None:
     from .config_change_investigation_demo import default_demo_root, run_demo
 
-    demo_root = Path(args.demo_root).resolve() if args.demo_root else default_demo_root()
+    demo_root = _demo_root_path(args.demo_root, default_demo_root())
     result = run_demo(demo_root=demo_root)
 
     print(f"[OK] Loaded {result['change_event_count']} config changes")
@@ -270,6 +270,15 @@ def _display_path(path: Path) -> str:
         return resolved.as_posix()
 
 
+def _demo_root_path(value: str | None, default_root: Path) -> Path:
+    demo_root = Path(value).resolve() if value else default_root.resolve()
+    if not demo_root.exists():
+        raise FileNotFoundError(f"Demo root not found: {demo_root}")
+    if not demo_root.is_dir():
+        raise ValueError(f"Demo root path is not a directory: {demo_root}")
+    return demo_root
+
+
 def _validate_run_config(config: Mapping[str, Any]) -> dict[str, Any]:
     time_config = _optional_mapping(config.get("time", {}), "time")
     feature_config = _optional_mapping(config.get("features", {}), "features")

tests/test_cli_errors.py

@@ -255,6 +255,37 @@ def test_main_reports_file_plot_output_dir_without_traceback(tmp_path, capsys) -
     assert "Traceback" not in stderr
 
 
+@pytest.mark.parametrize(
+    "command",
+    ["run-ai-demo", "run-rule-dedup-demo", "run-config-change-demo"],
+)
+def test_main_reports_file_demo_root_without_traceback(command, tmp_path, capsys) -> None:
+    demo_root = tmp_path / "demo-root"
+    demo_root.write_text("not a directory\n", encoding="utf-8")
+
+    with pytest.raises(SystemExit) as excinfo:
+        main([command, "--demo-root", str(demo_root)])
+
+    assert excinfo.value.code == 1
+    stderr = capsys.readouterr().err
+    assert stderr.startswith("error: ")
+    assert "Demo root path is not a directory" in stderr
+    assert "Traceback" not in stderr
+
+
+def test_main_reports_missing_demo_root_without_traceback(tmp_path, capsys) -> None:
+    demo_root = tmp_path / "missing-demo-root"
+
+    with pytest.raises(SystemExit) as excinfo:
+        main(["run-ai-demo", "--demo-root", str(demo_root)])
+
+    assert excinfo.value.code == 1
+    stderr = capsys.readouterr().err
+    assert stderr.startswith("error: ")
+    assert "Demo root not found" in stderr
+    assert "Traceback" not in stderr
+
+
 def test_main_reports_directory_plot_artifact_without_traceback(tmp_path, capsys) -> None:
     features_path = tmp_path / "features.csv"
     features_path.write_text(