fix(seo): a school is publishable on any year's results, not the latest

_school_sitemap_rows tested only the latest year's row, which quietly dropped
every school with results in its history but a null row for the most recent
year — a school that stopped reporting, or whose figures were suppressed for
small-cohort disclosure.

The Mallard Academy (150367) is the case that caught it: real KS2 results for
2015-16 through 2018-19, then null rows from 2022-23 on. Its detail page shows
all four years; the sitemap omitted it. Sampling 40 of the 2,206 excluded
schools found 4 like this, so roughly 220 real pages were being withheld.

Publishable is now a property of the school, computed across every row, while
lastmod still comes from the latest row so the most recent Ofsted date wins.
The field list is a module constant shared with _has_publishable_data so the
two checks cannot drift.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_015mWQnpye9F299NVRCCSRvj

backend/tests/test_sitemap.py

@@ -176,3 +176,44 @@ def test_children_are_chunked_under_the_limit(monkeypatch):
 def test_build_sitemap_still_returns_the_index(sitemap):
     # lifespan and the admin endpoint call build_sitemap(); keep it working.
     assert "<sitemapindex" in sitemap
+
+
+def test_school_with_results_in_an_earlier_year_is_still_listed(monkeypatch):
+    """Regression: The Mallard Academy (150367).
+
+    Real KS2 results 2015-16 to 2018-19, then null rows from 2022-23 onward
+    because the school stopped reporting. The first cut tested the latest
+    year's row alone and dropped it, along with ~220 others, even though its
+    detail page shows all four years of results.
+    """
+    from backend import app as app_module
+    import pandas as _pd
+
+    base = {"local_authority": "Testshire", "school_type": "Academy",
+            "phase": "Primary", "ofsted_date": None, "ofsted_grade": np.nan,
+            "attainment_8_score": np.nan, "urn": 150367,
+            "school_name": "Mallard Academy"}
+    df = _pd.DataFrame([
+        {**base, "year": 201819, "rwm_expected_pct": 67.0},
+        {**base, "year": 202324, "rwm_expected_pct": np.nan},
+        {**base, "year": 202425, "rwm_expected_pct": np.nan},
+    ])
+    monkeypatch.setattr(app_module, "load_school_data", lambda: df)
+
+    xml = app_module.build_sitemaps()["schools-1.xml"]
+    assert "/school/150367-mallard-academy" in xml
+
+
+def test_school_with_no_results_in_any_year_is_still_omitted(monkeypatch):
+    """The fix must not turn into "list everything"."""
+    from backend import app as app_module
+    import pandas as _pd
+
+    base = {"local_authority": "Testshire", "school_type": "Academy",
+            "phase": "Primary", "ofsted_date": None, "ofsted_grade": np.nan,
+            "attainment_8_score": np.nan, "rwm_expected_pct": np.nan,
+            "urn": 100002, "school_name": "Ghost Primary"}
+    df = _pd.DataFrame([{**base, "year": y} for y in (202324, 202425)])
+    monkeypatch.setattr(app_module, "load_school_data", lambda: df)
+
+    assert "/school/100002" not in app_module.build_sitemaps()["schools-1.xml"]