fix(pipeline): decode GIAS extracts as Windows-1252

GIAS publishes its CSVs in Windows-1252 and sends no charset. The tap read
resp.text, so requests guessed the codec, and the encoding="latin-1" passed
to read_csv did nothing on already-decoded text. On 3 Oct 2026 the guess was
windows-1250, and "St Thomas à Becket" (138950, 149557) was stored as
"St Thomas ŕ Becket". A different guess on another day would garble other
accented names.

Both streams now decode the downloaded bytes themselves (gias_csv.py). A byte
Windows-1252 leaves undefined becomes U+FFFD with a logged warning instead of
failing the load, so one odd name cannot stop the daily refresh. None of the
nine extracts checked (1 Jul to 3 Oct 2026) contains such a byte.

Checked by running the tap on the real 3 Oct extract with .text forced to
windows-1250: all 52,586 rows decode, with no "ŕ" and no replacement
characters.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

e2e/tests/journeys.spec.ts

@@ -410,6 +410,29 @@ test('search and the school page agree on how many pupils a secondary has', asyn
   expect(school.total_pupils).toBe(detail.school_info.total_pupils);
 });
 
+test('a secondary search row compares its Attainment 8 with the LA average', async ({ page }) => {
+  // The comparison vanished unnoticed: the averages were fetched with
+  // force-cache, so one stored failure hid it in that browser for good.
+  // Playwright disables the HTTP cache when it intercepts requests, so this
+  // guards the comparison itself; the unit test pins the cache mode.
+  const la = await (await page.request.get('/api/la-averages')).json();
+  const averages: Record<string, number> = la.secondary?.attainment_8_by_la ?? {};
+  const res = await page.request.get('/api/schools?search=school&phase=secondary&page_size=50');
+  expect(res.ok()).toBeTruthy();
+  const school = ((await res.json()).schools ?? []).find(
+    (s: { attainment_8_score?: number | null; local_authority?: string; school_type?: string }) =>
+      s.attainment_8_score != null && s.local_authority != null && averages[s.local_authority] != null
+      && !/special|pupil referral|alternative provision/i.test(s.school_type ?? ''));
+  test.skip(!school, 'no mainstream secondary with an LA average here');
+
+  await searchByName(page, school.school_name);
+  const link = page.locator(`a[href^="/school/${school.urn}-"]`).first();
+  await expect(link).toBeVisible({ timeout: 15_000 });
+  const stats = link.locator('xpath=ancestor::div[contains(@class, "__rowContent")][1]')
+    .locator('[class*="__line3"]');
+  await expect(stats.getByText(/vs LA avg/)).toBeVisible();
+});
+
 test('a phase outside primary/secondary filters to that phase, not to everything', async ({ page }) => {
   // The search page offers every GIAS phase, but the API only knew the grouped
   // ones and silently dropped the rest — so "Nursery" returned primaries.

nextjs-app/__tests__/components/HomeView.staleFetch.test.tsx

@@ -1,6 +1,6 @@
 import { act, fireEvent, render, screen } from '@testing-library/react';
 import { HomeView } from '@/components/HomeView';
-import { fetchSchools } from '@/lib/api';
+import { fetchLAaverages, fetchSchools } from '@/lib/api';
 import { primaryFixture } from '../support/schoolFixtures';
 import type { SchoolsResponse, School } from '@/lib/types';
 
@@ -84,3 +84,23 @@ test('failed map requests can be retried by reopening the map', async () => {
   expect(fetchSchools).toHaveBeenCalledTimes(2);
   expect(screen.getByTestId('map')).toHaveTextContent('Retry result');
 });
+
+test('LA averages are not fetched with force-cache, so one failure is not replayed for good', async () => {
+  // force-cache serves any stored response, however old, without asking the
+  // server. A request that failed once (a staging deploy restart, the July
+  // proxy outage) was stored and replayed on every later visit, and the
+  // "vs LA avg" delta vanished from every secondary row in that browser.
+  // The default mode honours the API's Cache-Control and never reuses an
+  // error.
+  params = new URLSearchParams('search=high');
+  const secondary: SchoolsResponse = {
+    ...response('Alpha High'),
+    schools: [{ ...primaryFixture.schoolInfo, school_name: 'Alpha High', phase: 'Secondary', attainment_8_score: 50 }],
+  };
+  render(<HomeView initialSchools={secondary} filters={filters} />);
+  await act(async () => {});
+  expect(fetchLAaverages).toHaveBeenCalled();
+  for (const [options] of jest.mocked(fetchLAaverages).mock.calls) {
+    expect(options?.cache).not.toBe('force-cache');
+  }
+});

nextjs-app/components/HomeView.tsx

@@ -358,10 +358,14 @@ export function HomeView({ initialSchools, filters, totalSchools, howItWorks, ed
     return () => controller.abort();
   }, [resultsView, searchParams, initialSchools.schools]);
 
-  // Fetch LA averages when secondary or mixed schools are visible
+  // Fetch LA averages when secondary or mixed schools are visible. Default
+  // cache mode, never force-cache: force-cache replays any stored response
+  // without asking the server, so one failed request (a deploy restart) hid
+  // every "vs LA avg" delta in that browser for good. The API's Cache-Control
+  // already lets the browser reuse a good answer for five minutes.
   useEffect(() => {
     if (!isSecondaryView && !isMixedView) return;
-    fetchLAaverages({ cache: 'force-cache' })
+    fetchLAaverages()
       .then(data => setLaAverages(data.secondary.attainment_8_by_la))
       .catch(() => {});
   }, [isSecondaryView, isMixedView]);

pipeline/plugins/extractors/tap-uk-gias/tap_uk_gias/gias_csv.py

@@ -0,0 +1,26 @@
+"""Read a GIAS extract from the raw bytes of the download.
+
+GIAS writes its CSVs in Windows-1252 and sends no charset, so `resp.text`
+leaves requests to guess the codec. On 3 Oct 2026 it guessed windows-1250 and
+"à" became "ŕ". Decode the bytes ourselves instead.
+"""
+
+from __future__ import annotations
+
+import io
+
+import pandas as pd
+
+GIAS_ENCODING = "cp1252"
+
+
+def read_gias_csv(content: bytes, logger=None) -> pd.DataFrame:
+    """Every column as a string; a blank cell stays ''."""
+    # Windows-1252 leaves five bytes undefined. One stray byte must not stop
+    # the daily refresh of every school, so it becomes U+FFFD and is logged.
+    text = content.decode(GIAS_ENCODING, errors="replace")
+    undecodable = text.count("�")
+    if undecodable and logger is not None:
+        logger.warning("%d byte(s) in the GIAS extract could not be decoded as %s",
+                       undecodable, GIAS_ENCODING)
+    return pd.read_csv(io.StringIO(text), dtype=str, keep_default_na=False)

pipeline/plugins/extractors/tap-uk-gias/tap_uk_gias/tap.py

@@ -7,6 +7,8 @@ from datetime import date, timedelta
 from singer_sdk import Stream, Tap
 from singer_sdk import typing as th
 
+from tap_uk_gias.gias_csv import read_gias_csv
+
 GIAS_URL_TEMPLATE = (
     "https://ea-edubase-api-prod.azurewebsites.net"
     "/edubase/downloads/public/edubasealldata{date}.csv"
@@ -74,9 +76,6 @@ class GIASEstablishmentsStream(Stream):
 
     def get_records(self, context):
         """Download GIAS CSV and yield rows."""
-        import io
-
-        import pandas as pd
         import requests
 
         today = date.today()
@@ -94,12 +93,7 @@ class GIASEstablishmentsStream(Stream):
 
         resp.raise_for_status()
 
-        df = pd.read_csv(
+        df = read_gias_csv(resp.content, self.logger)
-            io.StringIO(resp.text),
-            encoding="latin-1",
-            dtype=str,
-            keep_default_na=False,
-        )
 
         for _, row in df.iterrows():
             record = row.to_dict()
@@ -126,9 +120,6 @@ class GIASLinksStream(Stream):
 
     def get_records(self, context):
         """Download GIAS links CSV and yield rows."""
-        import io
-
-        import pandas as pd
         import requests
 
         today = date.today()
@@ -146,12 +137,7 @@ class GIASLinksStream(Stream):
 
         resp.raise_for_status()
 
-        df = pd.read_csv(
+        df = read_gias_csv(resp.content, self.logger)
-            io.StringIO(resp.text),
-            encoding="latin-1",
-            dtype=str,
-            keep_default_na=False,
-        )
 
         for _, row in df.iterrows():
             record = row.to_dict()

pipeline/tests/test_gias_encoding.py

@@ -0,0 +1,66 @@
+"""GIAS publishes its extracts in Windows-1252 and declares no charset.
+
+The tap used to hand pandas `resp.text`, so requests guessed the codec.
+On 3 Oct 2026 it guessed windows-1250, and "St Thomas à Becket" was stored
+as "St Thomas ŕ Becket". The `encoding=` passed to read_csv did nothing,
+because the text was already decoded.
+"""
+import importlib.util
+import logging
+from pathlib import Path
+
+import pytest
+
+MODULE = (Path(__file__).resolve().parents[1] / 'plugins' / 'extractors' / 'tap-uk-gias'
+          / 'tap_uk_gias' / 'gias_csv.py')
+
+
+@pytest.fixture
+def gias_csv():
+    spec = importlib.util.spec_from_file_location('gias_csv', MODULE)
+    module = importlib.util.module_from_spec(spec)
+    spec.loader.exec_module(module)
+    return module
+
+
+# Byte for byte as GIAS writes it: 0xE0 à, 0x92 ’, 0xE9 é, 0xB0 °, 0xE7 ç.
+EXTRACT = (
+    b'"URN","EstablishmentName","HeadLastName"\r\n'
+    b'"138950","St Thomas \xe0 Becket Catholic Secondary School","Smith"\r\n'
+    b'"100000","The Dean and Chapter of St Paul\x92s Cathedral","Pr\xe9vert"\r\n'
+    b'"140677","North Star 180\xb0","Fran\xe7ois"\r\n'
+    b'"100001","No head recorded",""\r\n'
+)
+
+
+def test_names_decode_as_windows_1252(gias_csv):
+    df = gias_csv.read_gias_csv(EXTRACT)
+    assert list(df['EstablishmentName']) == [
+        'St Thomas à Becket Catholic Secondary School',
+        'The Dean and Chapter of St Paul’s Cathedral',
+        'North Star 180°',
+        'No head recorded',
+    ]
+    assert list(df['HeadLastName']) == ['Smith', 'Prévert', 'François', '']
+
+
+def test_the_codec_requests_guessed_is_not_used(gias_csv):
+    # What the tap stored on 3 Oct: the same bytes read as windows-1250.
+    assert 'ŕ' in EXTRACT.decode('cp1250')
+    names = ' '.join(gias_csv.read_gias_csv(EXTRACT)['EstablishmentName'])
+    assert 'ŕ' not in names
+
+
+def test_values_stay_strings(gias_csv):
+    df = gias_csv.read_gias_csv(EXTRACT)
+    assert df.loc[0, 'URN'] == '138950'
+
+
+def test_a_byte_windows_1252_leaves_undefined_does_not_stop_the_load(gias_csv, caplog):
+    # 0x81 has no Windows-1252 character. One odd name must not block the daily
+    # refresh of every school, but it must be visible in the log.
+    extract = b'"URN","EstablishmentName"\r\n"100002","Odd \x81 Name"\r\n'
+    with caplog.at_level(logging.WARNING):
+        df = gias_csv.read_gias_csv(extract, logger=logging.getLogger('gias'))
+    assert df.loc[0, 'EstablishmentName'] == 'Odd � Name'
+    assert 'could not be decoded' in caplog.text