Deplace l'overlay Cocoa derriere le contrat Overlay, sans le modifier

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

tests/test_interface.py

@@ -0,0 +1,16 @@
+"""La fabrique rend un overlay conforme au contrat, sans ouvrir de fenêtre."""
+import pytest
+
+from interface import classe_overlay_pour
+
+
+def test_l_overlay_macos_declare_tout_le_contrat():
+    classe = classe_overlay_pour("darwin")
+    for methode in ("show", "hide", "set_level", "set_status", "rearmer_garde"):
+        assert callable(getattr(classe, methode, None)), f"{methode} manque"
+
+
+def test_une_plateforme_inconnue_est_refusee_clairement():
+    with pytest.raises(NotImplementedError) as e:
+        classe_overlay_pour("haiku-os")
+    assert "haiku-os" in str(e.value)