fix(api): fall back to legacy name-column query when marts predate code migration

Closes the deploy window flagged by CI review — the backend now works
against both the old (name) and new (code) mart schemas.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

backend/data_loader.py

@@ -262,25 +262,66 @@ assert "NULL AS has_sixth_form" in str(_MAIN_QUERY_NO_SIXTH_FORM), (
     "expected replacement of 's.has_sixth_form,' to have taken effect"
 )
 
+# Fallback used when marts.dim_school predates the GIAS code-dictionary
+# migration (i.e. the nightly dbt pipeline hasn't rebuilt the mart yet on
+# this DB, so it still has the old name columns instead of *_code columns).
+_MAIN_QUERY_LEGACY_NAMES = str(_MAIN_QUERY)
+_LEGACY_NAME_REPLACEMENTS = [
+    ("s.phase_code,", "s.phase,"),
+    ("s.school_type_code,", "s.school_type,"),
+    (
+        "s.religious_character_code,",
+        "s.religious_character AS religious_denomination,",
+    ),
+    ("s.status_code,", "s.status,"),
+    ("s.admissions_policy_code,", "s.admissions_policy,"),
+]
+for _old, _new in _LEGACY_NAME_REPLACEMENTS:
+    assert _old in _MAIN_QUERY_LEGACY_NAMES, (
+        f"expected {_old!r} to be present in _MAIN_QUERY before replacement"
+    )
+    _MAIN_QUERY_LEGACY_NAMES = _MAIN_QUERY_LEGACY_NAMES.replace(_old, _new)
+_MAIN_QUERY_LEGACY_NAMES = text(_MAIN_QUERY_LEGACY_NAMES)
+
+_GIAS_CODE_COLUMN_NAMES = (
+    "phase_code",
+    "school_type_code",
+    "religious_character_code",
+    "status_code",
+    "admissions_policy_code",
+)
+
 
 def load_school_data_as_dataframe() -> pd.DataFrame:
     """Load all school + KS2 data as a pandas DataFrame."""
     try:
         df = pd.read_sql(_MAIN_QUERY, engine)
     except sqlalchemy.exc.ProgrammingError as exc:
-        if "has_sixth_form" not in str(exc):
+        if any(col in str(exc) for col in _GIAS_CODE_COLUMN_NAMES):
+            logging.getLogger(__name__).warning(
+                "marts predate the GIAS code migration — falling back to "
+                "legacy name-column query: %s",
+                exc,
+            )
+            try:
+                df = pd.read_sql(_MAIN_QUERY_LEGACY_NAMES, engine)
+            except Exception as exc2:
+                print(f"Warning: Could not load school data from marts: {exc2}")
+                return pd.DataFrame()
+        elif "has_sixth_form" in str(exc):
+            logging.getLogger(__name__).warning(
+                "marts.dim_school is missing has_sixth_form (pipeline hasn't "
+                "rebuilt the mart yet on this DB) — retrying without it: %s",
+                exc,
+            )
+            try:
+                df = pd.read_sql(_MAIN_QUERY_NO_SIXTH_FORM, engine)
+            except Exception as exc2:
+                print(f"Warning: Could not load school data from marts: {exc2}")
+                return pd.DataFrame()
+        else:
             print(f"Warning: Could not load school data from marts: {exc}")
             return pd.DataFrame()
-        logging.getLogger(__name__).warning(
-            "marts.dim_school is missing has_sixth_form (pipeline hasn't "
-            "rebuilt the mart yet on this DB) — retrying without it: %s",
-            exc,
-        )
-        try:
-            df = pd.read_sql(_MAIN_QUERY_NO_SIXTH_FORM, engine)
-        except Exception as exc2:
-            print(f"Warning: Could not load school data from marts: {exc2}")
-            return pd.DataFrame()
     except Exception as exc:
         print(f"Warning: Could not load school data from marts: {exc}")
         return pd.DataFrame()