diff --git a/tests/test_palier12.py b/tests/test_palier12.py
new file mode 100644
index 0000000..314755c
--- /dev/null
+++ b/tests/test_palier12.py
@@ -0,0 +1,49 @@
+"""Palier 12 (0.15.0): header unifié desktop/mobile (issue #16)."""
+
+
+def test_shared_header_on_app_pages(client, fake_gitea):
+    for path in ("/", "/focus", "/today", "/briefing", "/forecast",
+                 "/rules", "/health", "/standup", "/capture"):
+        page = client.get(path)
+        assert page.status_code == 200, path
+        assert page.text.count('id="nav-more-btn"') == 1, path
+        assert page.text.count('id="nav-burger"') == 1, path
+        assert page.text.count('id="mobile-nav"') == 1, path
+        assert "/static/js/nav.js" in page.text, path
+        # Primaires visibles, secondaires dans le menu « Plus ».
+        assert 'href="/today"' in page.text
+        assert 'href="/health"' in page.text  # présent (menu Plus/mobile)
+        assert 'class="nav-pills main-nav"' in page.text
+
+
+def test_active_states(client, fake_gitea):
+    home = client.get("/")
+    assert 'href="/" class="nav-pill active"' in home.text
+    forecast = client.get("/forecast")
+    # La page active est dans « Plus » : bouton marqué + lien actif.
+    assert "active-soft" in forecast.text
+    assert 'href="/forecast" class="nav-pill active"' in forecast.text
+    today = client.get("/today")
+    assert 'href="/today" class="nav-pill active"' in today.text
+
+
+def test_board_header_crumb_and_gitea_link(client, fake_gitea):
+    board = client.get("/board/Projets/demo")
+    assert board.status_code == 200
+    assert 'href="/board/Projets/demo"' in board.text  # fil d'Ariane
+    assert "Gitea ↗" in board.text
+    assert 'id="nav-burger"' in board.text
+
+
+def test_wall_has_no_app_header(client, fake_gitea):
+    wall = client.get("/wall")
+    assert wall.status_code == 200
+    assert 'id="nav-burger"' not in wall.text  # plein écran TV assumé
+
+
+def test_nav_js_contract(client, fake_gitea):
+    js = client.get("/static/js/nav.js")
+    assert js.status_code == 200
+    assert "nav-burger" in js.text
+    assert "Escape" in js.text
+    assert "aria-expanded" in js.text