test: cover Kanban view toggle config validation

tests/test_kanban_view_toggle.py

@@ -7,6 +7,7 @@ shared Kanban config so reloads and other browsers see the same mode.
 
 from pathlib import Path
 import re
+from types import SimpleNamespace
 
 import pytest
 
@@ -87,6 +88,19 @@ def test_kanban_config_patch_persists_lane_by_profile_to_config_yaml(tmp_path, m
         encoding="utf-8",
     )
     monkeypatch.setattr(config, "_get_config_path", lambda: cfg_path)
+    monkeypatch.setattr(
+        bridge,
+        "_config_payload",
+        lambda: {
+            "columns": [],
+            "assignees": [],
+            "default_tenant": "",
+            "lane_by_profile": True,
+            "include_archived_by_default": False,
+            "render_markdown": True,
+            "read_only": False,
+        },
+    )
     config.reload_config()
 
     payload = bridge._update_config_payload({"lane_by_profile": False})
@@ -102,3 +116,28 @@ def test_kanban_config_patch_rejects_non_boolean_lane_by_profile():
 
     with pytest.raises(ValueError, match="lane_by_profile must be boolean"):
         bridge._update_config_payload({"lane_by_profile": "false"})
+
+
+def test_kanban_config_patch_validation_returns_clean_400(monkeypatch):
+    import api.kanban_bridge as bridge
+
+    captured = {}
+
+    def fake_bad(handler, msg, status=400):
+        captured["msg"] = msg
+        captured["status"] = status
+        return True
+
+    monkeypatch.setattr(bridge, "bad", fake_bad)
+
+    result = bridge.handle_kanban_patch(
+        object(),
+        SimpleNamespace(path="/api/kanban/config", query=""),
+        {"lane_by_profile": "false"},
+    )
+
+    assert result is True
+    assert captured == {
+        "msg": "lane_by_profile must be boolean",
+        "status": 400,
+    }