diff --git a/app.py b/app.py
index 20d2d89..00c43e0 100644
--- a/app.py
+++ b/app.py
@@ -30,7 +30,7 @@ from pynput import keyboard
 
 from controller import ZonzaController
 from core import CONFIG, validate_config
-from pulse_window import PulseWindow
+from interface import classe_overlay_pour
 from systeme import choisir_systeme
 
 _STATE_TITLES = {
@@ -49,7 +49,7 @@ class ZonzaApp(NSObject):
             return None
         self._item = None
         self._sounds_item = None
-        self.pulse = PulseWindow.alloc().init()
+        self.pulse = classe_overlay_pour().alloc().init()
         self.controller = ZonzaController(
             CONFIG, self.pulse, on_state=self._set_state,
             run_on_main=AppHelper.callAfter,
diff --git a/interface/__init__.py b/interface/__init__.py
new file mode 100644
index 0000000..5f6ca76
--- /dev/null
+++ b/interface/__init__.py
@@ -0,0 +1,11 @@
+"""Choisit l'implémentation d'overlay selon la plateforme."""
+import sys
+
+
+def classe_overlay_pour(plateforme=None):
+    """Rend la CLASSE d'overlay (pas une instance : Cocoa exige `alloc().init()`)."""
+    plateforme = plateforme or sys.platform
+    if plateforme.startswith("darwin"):
+        from interface.cocoa.overlay import PulseWindow
+        return PulseWindow
+    raise NotImplementedError(f"Aucune interface pour : {plateforme}")
diff --git a/interface/cocoa/__init__.py b/interface/cocoa/__init__.py
new file mode 100644
index 0000000..e69de29
diff --git a/pulse_window.py b/interface/cocoa/overlay.py
similarity index 100%
rename from pulse_window.py
rename to interface/cocoa/overlay.py
diff --git a/tests/test_interface.py b/tests/test_interface.py
new file mode 100644
index 0000000..9f40b79
--- /dev/null
+++ b/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)