§22 S2: @S2 acceptance — anonymous empty public collection catalog (C3.6)

Anonymous reader of an empty public collection gets a 200 empty catalog and no
propose action (the propose route rejects anonymous); the Catalog footer's
'Sign in to propose' prompt is the existing anonymous affordance.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

backend/tests/test_collection_scoped_serve.py

@@ -139,3 +139,21 @@ def test_scoped_routes_404_for_collection_outside_project(app_with_fake_gitea):
     with TestClient(app) as client:
         r = client.get("/api/projects/default/collections/nope/rfcs")
         assert r.status_code == 404
+
+
+def test_s2_anonymous_empty_public_collection(app_with_fake_gitea):
+    """C3.6 (@S2): a public collection with no entries; an anonymous visitor
+    lands on its catalog → an empty catalog (200, no items), and the propose
+    action is not available to them (the propose route rejects anonymous)."""
+    app, _ = app_with_fake_gitea
+    with TestClient(app) as client:
+        _add_features_collection()  # public, no entries
+        # Anonymous (no session cookie) reads the empty catalog — 200, [].
+        r = client.get("/api/projects/default/collections/features/rfcs")
+        assert r.status_code == 200, r.text
+        assert r.json()["items"] == []
+        # No propose action for an anonymous visitor.
+        r2 = client.post(
+            "/api/projects/default/collections/features/rfcs/propose",
+            json={"title": "X", "slug": "x", "pitch": "p", "tags": []})
+        assert r2.status_code == 401