Index: test/activitypub-as2.test.js
===================================================================
--- test/activitypub-as2.test.js	(revision 432831c4da84544aa40fc90ff67963b13ddfa657)
+++ test/activitypub-as2.test.js	(revision 432831c4da84544aa40fc90ff67963b13ddfa657)
@@ -0,0 +1,87 @@
+// AS2 / JSON-LD validity guard.
+//
+// Every property key and `type` value our ActivityPub objects emit MUST be either an AS2-core
+// (or security/v1) term OR declared in the federation @context (AP_CONTEXT). A new feature that
+// emits an undeclared term fails this test → declare it in AP_CONTEXT (extensions) or add it to
+// the AS2 allowlist below. This keeps Klonkt's output valid AS2/JSON-LD forever — not just
+// "Mastodon tolerates it". No extra deps; in-memory SQLite. Run: npm test
+import { test } from 'node:test';
+import assert from 'node:assert/strict';
+
+process.env.DATABASE_PATH = ':memory:';
+process.env.PUBLIC_BASE_URL = 'https://test.example';
+
+const dbMod = await import('../src/config/database.js');
+const db = dbMod.default;
+dbMod.initializeDatabase();
+const AP = (await import('../src/services/ActivityPubService.js')).default;
+
+const BASE = 'https://test.example';
+
+// AS2-core + security/v1 vocabulary Klonkt uses (stable — only extend when AS2/security itself
+// adds a term we adopt). JSON-LD keywords included.
+const AS2 = new Set([
+  '@context', '@id', '@type',
+  'id', 'type', 'actor', 'object', 'target', 'to', 'cc',
+  'content', 'name', 'summary', 'url', 'href', 'mediaType',
+  'published', 'updated', 'attributedTo', 'inReplyTo', 'replies',
+  'attachment', 'tag', 'icon', 'image', 'duration',
+  'totalItems', 'orderedItems', 'items', 'first', 'last', 'partOf', 'next', 'prev',
+  'preferredUsername', 'inbox', 'outbox', 'followers', 'following', 'endpoints', 'sharedInbox',
+  'publicKey', 'owner', 'publicKeyPem',
+  'Note', 'Person', 'Create', 'Update', 'Delete', 'Tombstone', 'Announce', 'Like', 'Follow',
+  'Accept', 'Reject', 'Undo', 'Add', 'Remove', 'Document', 'Image', 'Audio', 'Video',
+  'Mention', 'Link', 'Collection', 'OrderedCollection', 'OrderedCollectionPage',
+]);
+
+// The extension terms = exactly the keys declared in AP_CONTEXT's term-definition object.
+const ctxTerms = new Set();
+for (const part of AP.AP_CONTEXT) if (part && typeof part === 'object') for (const k of Object.keys(part)) ctxTerms.add(k);
+const allowed = new Set([...AS2, ...ctxTerms]);
+
+// Collect every property key + every `type` string value, recursively.
+function collect(obj, keys = new Set()) {
+  if (Array.isArray(obj)) { for (const x of obj) collect(x, keys); return keys; }
+  if (obj && typeof obj === 'object') {
+    for (const [k, v] of Object.entries(obj)) {
+      keys.add(k);
+      if (k === 'type' && typeof v === 'string') keys.add(v);
+      collect(v, keys);
+    }
+  }
+  return keys;
+}
+function assertValid(obj, label) {
+  const undeclared = [...collect(obj)].filter((k) => !allowed.has(k));
+  assert.deepEqual(undeclared, [],
+    `${label}: undeclared AS2/JSON-LD term(s) — declare in AP_CONTEXT (extension) or the AS2 allowlist: ${undeclared.join(', ')}`);
+}
+
+// Seed one site that exercises the extension-heavy actor fields (profile links → PropertyValue,
+// photo → icon, primary → featured).
+db.prepare('INSERT INTO users (id, username, email, password_hash, role) VALUES (?,?,?,?,?)').run('u1', 'u1', 'u1@test', 'x', 'god');
+db.prepare('INSERT INTO sites (id, slug, title, owner_id, is_primary, profile_links, profile_photo) VALUES (?,?,?,?,?,?,?)')
+  .run('s1', 'demo', 'Demo', 'u1', 1, JSON.stringify([{ platform: 'website', url: 'https://x.test' }]), '/media/x.png');
+const site = db.prepare('SELECT * FROM sites WHERE id = ?').get('s1');
+site.primary_slug = 'demo';
+
+// Kitchen-sink note: nsfw (→ sensitive + summary), a hashtag (→ Hashtag), a cover (→ attachment).
+const post = {
+  id: 'p1', slug: 'hello', title: 'Hi', content: '<p>hello #music</p>',
+  nsfw: 1, content_warning: 'cw', tags: JSON.stringify(['mood']),
+  cover_image_url: '/media/c.webp',
+  published_at: '2026-01-01T00:00:00Z', created_at: '2026-01-01T00:00:00Z',
+};
+
+test('actor is valid AS2 (every term declared)', () => assertValid(AP.buildActor(BASE, site), 'actor'));
+test('create+note is valid AS2 (every term declared)', () => assertValid(AP.buildCreate(BASE, site, post), 'create/note'));
+test('outbox/followers/featured collections are valid AS2', () => {
+  assertValid(AP.buildOutbox(BASE, site, [post]), 'outbox');
+  assertValid(AP.buildFollowers(BASE, site, 3), 'followers');
+  assertValid(AP.buildFollowing(BASE, site, 2), 'following');
+  assertValid(AP.buildFeatured(BASE, site, [post]), 'featured');
+});
+test('AP_CONTEXT declares every extension term we rely on', () => {
+  for (const t of ['sensitive', 'Hashtag', 'manuallyApprovesFollowers', 'discoverable', 'featured', 'PropertyValue', 'embedUrl'])
+    assert.ok(ctxTerms.has(t), `AP_CONTEXT must declare "${t}"`);
+});