fix(blog): confirmer l'état mémoire après sauvegarde

tests/unit/test_blog_state.py

@@ -425,4 +425,41 @@ def test_atomic_save_preserves_on_error(tmp_path: Path) -> None:
     assert state.get_known_guids() == frozenset({"original-guid-1", "original-guid-2", "new-guid"})
 
 
+def test_acknowledge_does_not_advance_memory_when_save_fails(
+    tmp_path: Path,
+) -> None:
+    """Conserve l'état précédent en mémoire si l'acquittement ne peut pas être sauvegardé.
+
+    :param tmp_path: Fixture pytest pour un répertoire temporaire.
+    :return: None
+    """
+    state_file = tmp_path / "state.json"
+    state = BlogRSSState(state_file)
+    state.add_guids(["existing-guid"])
+    state.update_cache_headers("old-etag", "old-last-modified")
+    article = BlogArticle(
+        id="new-guid",
+        title="Article",
+        url="https://example.com/article",
+        published_at=datetime(2026, 9, 12, 8, 0, tzinfo=UTC),
+        updated_at=None,
+        category=None,
+        author=None,
+        content_html="<p>Contenu</p>",
+        content_text="Contenu",
+    )
+
+    with patch.object(Path, "replace", side_effect=OSError("replace failed")):
+        state.acknowledge(
+            BlogRSSFetchResult(
+                articles=(article,),
+                etag="new-etag",
+                last_modified="new-last-modified",
+            )
+        )
+
+    assert state.get_known_guids() == frozenset({"existing-guid"})
+    assert state.get_cache_headers() == ("old-etag", "old-last-modified")
+
+
 # Ensure trailing newline