diff --git a/tests/test_palier15.py b/tests/test_palier15.py
new file mode 100644
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+++ b/tests/test_palier15.py
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+"""Palier 15 (0.19.0) — Performance + navigation Pilotage.
+
+- A : les boucles par dépôt sont parallélisées (le comportement
+  visible ne change pas — couvert par les paliers précédents) et
+  le cache du client passe en stale-while-revalidate (testé dans
+  test_gitea_client.py).
+- C : /forecast devient un tableau de bord des jalons (une ligne
+  par jalon, ancres depuis le dashboard) et /health un tableau
+  trié par sévérité, avec sélecteur de projet sur le détail.
+"""
+
+import asyncio
+
+import httpx
+
+from app.gitea_client import GiteaClient
+
+
+def test_forecast_is_a_portfolio_table(client):
+    r = client.get("/forecast")
+    assert r.status_code == 200
+    assert "pilot-table" in r.text
+    assert "jalon(s) ouvert(s)" in r.text
+    # One row for the demo milestone, anchored for dashboard links.
+    assert 'id="ms-Projets-demo"' in r.text
+    assert "Sprint 1" in r.text
+    # The per-project pace table is still there.
+    assert "Débit par projet" in r.text
+
+
+def test_dashboard_milestone_links_into_forecast(client):
+    r = client.get("/")
+    assert r.status_code == 200
+    assert 'href="/forecast#ms-Projets-demo"' in r.text
+
+
+def test_health_index_is_a_severity_table(client):
+    r = client.get("/health")
+    assert r.status_code == 200
+    assert "pilot-table" in r.text
+    assert "data-severity" in r.text
+    assert "Projets/demo" in r.text
+
+
+def test_health_detail_has_project_switcher(client):
+    r = client.get("/health/Projets/demo")
+    assert r.status_code == 200
+    assert 'id="health-switch"' in r.text
+    assert '<option value="Projets/demo" selected>' in r.text
+    assert "tous les projets" in r.text
+
+
+async def test_swr_serves_stale_then_refreshes_in_background():
+    """Stale entries are served instantly; the refresh lands
+    asynchronously and the next read sees the fresh value."""
+    calls = {"n": 0}
+
+    def handler(request):
+        if request.url.path.endswith("/user"):
+            return httpx.Response(200, json={"id": 7})
+        calls["n"] += 1
+        return httpx.Response(200, json={"data": [{"id": calls["n"]}]})
+
+    client = GiteaClient(
+        base_url="http://gitea.test",
+        token="",
+        cache_ttl=60,
+        transport=httpx.MockTransport(handler),
+    )
+    first = await client.search_repos()
+    assert first == [{"id": 1}]
+    # Fresh cache: no new fetch.
+    assert await client.search_repos() == [{"id": 1}]
+    assert calls["n"] == 1
+    # Age the entry beyond the TTL: the stale value comes back
+    # immediately (same content, no wait)…
+    ts, value = client._cache["search_repos"]
+    client._cache["search_repos"] = (ts - 120, value)
+    assert await client.search_repos() == [{"id": 1}]
+    # …and the background refresh replaces it.
+    await asyncio.sleep(0.3)
+    assert await client.search_repos() == [{"id": 2}]
+    await client.aclose()
+
+
+async def test_swr_mutation_clear_blocks_stale_resurrection():
+    """A refresh started before a cache clear (mutation) must not
+    put its now-stale result back."""
+    calls = {"n": 0}
+
+    def handler(request):
+        if request.url.path.endswith("/user"):
+            return httpx.Response(200, json={"id": 7})
+        calls["n"] += 1
+        return httpx.Response(200, json={"data": [{"id": calls["n"]}]})
+
+    client = GiteaClient(
+        base_url="http://gitea.test",
+        token="",
+        cache_ttl=60,
+        transport=httpx.MockTransport(handler),
+    )
+    await client.search_repos()
+    ts, value = client._cache["search_repos"]
+    client._cache["search_repos"] = (ts - 120, value)
+    await client.search_repos()  # triggers background refresh
+    client._cache_clear()  # a mutation lands first
+    await asyncio.sleep(0.3)
+    # The cache was cleared and the in-flight refresh was disarmed:
+    # the next read fetches fresh instead of serving the old value.
+    assert await client.search_repos() == [{"id": 3}]
+    await client.aclose()