feat(combos): add Combos & Synergies detection, chip-style UI with dual hover; JSON persistence and headless honoring; stage ordering; docs and tests; bump to v2.2.1

code/tests/test_diagnostics_page.py

@@ -0,0 +1,24 @@
+from __future__ import annotations
+
+import importlib
+from starlette.testclient import TestClient
+
+
+def test_diagnostics_page_gated_and_visible(monkeypatch):
+    # Ensure disabled first
+    monkeypatch.delenv("SHOW_DIAGNOSTICS", raising=False)
+    import code.web.app as app_module
+    importlib.reload(app_module)
+    client = TestClient(app_module.app)
+    r = client.get("/diagnostics")
+    assert r.status_code == 404
+
+    # Enabled: should render
+    monkeypatch.setenv("SHOW_DIAGNOSTICS", "1")
+    importlib.reload(app_module)
+    client2 = TestClient(app_module.app)
+    r2 = client2.get("/diagnostics")
+    assert r2.status_code == 200
+    body = r2.text
+    assert "Diagnostics" in body
+    assert "Combos & Synergies" in body