Add Latin, and a test so the language list cannot drift

apps/web/src/lib/partners.js

@@ -57,7 +57,7 @@ const LANGUAGE_CODES = new Set([
   'ca','ce','ch','co','cr','cs','cu','cv','cy','da','de','dv','dz','ee','el','en','eo','es','et','eu','fa','ff',
   'fi','fj','fo','fr','fy','ga','gd','gl','gn','gu','gv','ha','he','hi','ho','hr','ht','hu','hy','hz','ia','id',
   'ie','ig','ii','ik','io','is','it','iu','ja','jv','ka','kg','ki','kj','kk','kl','km','kn','ko','kr','ks','ku',
-  'kv','kw','ky','lb','lg','li','ln','lo','lt','lu','lv','mg','mh','mi','mk','ml','mn','mr','ms','mt','my','na',
+  'kv','kw','ky','la','lb','lg','li','ln','lo','lt','lu','lv','mg','mh','mi','mk','ml','mn','mr','ms','mt','my','na',
   'nb','nd','ne','ng','nl','nn','no','nr','nv','ny','oc','oj','om','or','os','pa','pi','pl','ps','pt','qu','rm',
   'rn','ro','ru','rw','sa','sc','sd','se','sg','si','sk','sl','sm','sn','so','sq','sr','ss','st','su','sv','sw',
   'ta','te','tg','th','ti','tk','tl','tn','to','tr','ts','tt','tw','ty','ug','uk','ur','uz','ve','vi','vo','wa',

apps/web/test/partner-niches.test.js

@@ -0,0 +1,36 @@
+import assert from 'node:assert/strict';
+import { readFile } from 'node:fs/promises';
+import { test } from 'node:test';
+
+/**
+ * The niche picker hides ISO 639-1 codes, because feeds tag themselves with
+ * their language and those outrank real subjects. The list was hand-written
+ * and shipped one short: Latin reached the live sign-up form as a checkbox
+ * reading "la". A hand-kept list drifts, so this holds it to the standard.
+ */
+const CANONICAL = `aa ab ae af ak am an ar as av ay az ba be bg bh bi bm bn bo br bs ca ce ch co cr cs cu cv cy da de
+dv dz ee el en eo es et eu fa ff fi fj fo fr fy ga gd gl gn gu gv ha he hi ho hr ht hu hy hz ia id ie ig ii ik io is
+it iu ja jv ka kg ki kj kk kl km kn ko kr ks ku kv kw ky la lb lg li ln lo lt lu lv mg mh mi mk ml mn mr ms mt my na
+nb nd ne ng nl nn no nr nv ny oc oj om or os pa pi pl ps pt qu rm rn ro ru rw sa sc sd se sg si sk sl sm sn so sq sr
+ss st su sv sw ta te tg th ti tk tl tn to tr ts tt tw ty ug uk ur uz ve vi vo wa wo xh yi yo za zh zu`
+  .split(/\s+/)
+  .filter(Boolean);
+
+test('every ISO 639-1 code is excluded from the niche picker', async () => {
+  const src = await readFile(new URL('../src/lib/partners.js', import.meta.url), 'utf8');
+  const block = src.match(/const LANGUAGE_CODES = new Set\(\[([\s\S]*?)\]\);/)?.[1];
+  assert.ok(block, 'the LANGUAGE_CODES set should be findable');
+  const listed = new Set([...block.matchAll(/'([a-z]{2})'/g)].map((m) => m[1]));
+
+  const missing = CANONICAL.filter((code) => !listed.has(code));
+  assert.deepEqual(missing, [], `these languages would be offered as niches: ${missing.join(', ')}`);
+});
+
+test('real two-letter subjects are still offered', async () => {
+  const src = await readFile(new URL('../src/lib/partners.js', import.meta.url), 'utf8');
+  const block = src.match(/const LANGUAGE_CODES = new Set\(\[([\s\S]*?)\]\);/)?.[1];
+  const listed = new Set([...block.matchAll(/'([a-z]{2})'/g)].map((m) => m[1]));
+  // The whole reason the codes are excluded by name rather than by length.
+  assert.equal(listed.has('ai'), false, 'ai is a subject, not a language');
+  assert.equal(listed.has('go'), false, 'go is a subject, not a language');
+});