feat(api): translate GIAS codes to names at the query boundary

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

backend/tests/test_gias_translation.py

@@ -0,0 +1,44 @@
+"""API-boundary translation: marts now carry GIAS codes; the DataFrame the
+rest of the backend sees must carry today's name strings."""
+
+import numpy as np
+import pandas as pd
+
+from backend.data_loader import translate_gias_code_columns
+from backend.gias_codes import ESTABLISHMENT_STATUS, PHASE_OF_EDUCATION
+
+
+def _code_for(mapping, name):
+    return next(c for c, n in mapping.items() if n == name)
+
+
+def test_codes_become_todays_names():
+    df = pd.DataFrame([{
+        "urn": 1,
+        "phase_code": float(_code_for(PHASE_OF_EDUCATION, "Primary")),
+        "school_type_code": np.nan,
+        "status_code": float(_code_for(ESTABLISHMENT_STATUS, "Open, but proposed to close")),
+        "religious_character_code": np.nan,
+        "admissions_policy_code": np.nan,
+    }])
+    out = translate_gias_code_columns(df)
+    row = out.iloc[0]
+    assert row["phase"] == "Primary"
+    assert row["status"] == "Open, but proposed to close"
+    assert row["school_type"] is None
+    assert row["religious_denomination"] is None
+    assert row["admissions_policy"] is None
+
+
+def test_unknown_code_degrades_not_blanks():
+    df = pd.DataFrame([{"urn": 1, "phase_code": 9999.0}])
+    out = translate_gias_code_columns(df)
+    assert out.iloc[0]["phase"] == "Unknown (9999)"
+
+
+def test_missing_code_columns_are_a_noop():
+    """Old-schema DataFrames (tests, pre-pipeline DBs) pass through untouched."""
+    df = pd.DataFrame([{"urn": 1, "phase": "Primary", "status": "Open"}])
+    out = translate_gias_code_columns(df)
+    assert out.iloc[0]["phase"] == "Primary"
+    assert out.iloc[0]["status"] == "Open"