fix(security): block guest access to hidden/client-only photos across bulk + secure routes (stable) (#940)

* fix(security): block guest access to hidden/client-only photos across bulk + secure routes

* fix(security): harden hidden-photo fix per review (stale ZIP cache, legacy token mint, SQLite bool, client rebuild)

* fix(security): invalidate ZIP cache on photo visibility/category change (codex r2)

* fix(security): recheck photo visibility at signed/secure serve time (TOCTOU) + invalidate ZIP on client visibility change (codex r3)

---------

Co-authored-by: Paul Nothaft <[email protected]>

backend/__tests__/utils/photoVisibility.test.js

@@ -0,0 +1,40 @@
+/**
+ * Unit tests for the shared hidden-photo access-control helper.
+ *
+ * Pins the rule that ordinary gallery guests never receive photos with
+ * visibility='hidden' (NULL = visible), while PIN-clients see everything.
+ */
+const {
+  canSeeHiddenPhotos,
+  isPhotoHiddenFromViewer,
+} = require('../../src/utils/photoVisibility');
+
+describe('canSeeHiddenPhotos', () => {
+  it('is true only for the client access level', () => {
+    expect(canSeeHiddenPhotos('client')).toBe(true);
+    expect(canSeeHiddenPhotos('guest')).toBe(false);
+    expect(canSeeHiddenPhotos('slideshow')).toBe(false);
+    expect(canSeeHiddenPhotos(undefined)).toBe(false);
+  });
+});
+
+describe('isPhotoHiddenFromViewer', () => {
+  it('blocks a hidden photo from guests', () => {
+    expect(isPhotoHiddenFromViewer({ visibility: 'hidden' }, 'guest')).toBe(true);
+    expect(isPhotoHiddenFromViewer({ visibility: 'hidden' }, 'slideshow')).toBe(true);
+  });
+
+  it('lets clients see hidden photos', () => {
+    expect(isPhotoHiddenFromViewer({ visibility: 'hidden' }, 'client')).toBe(false);
+  });
+
+  it('treats visible and NULL visibility as viewable by everyone', () => {
+    expect(isPhotoHiddenFromViewer({ visibility: 'visible' }, 'guest')).toBe(false);
+    expect(isPhotoHiddenFromViewer({ visibility: null }, 'guest')).toBe(false);
+    expect(isPhotoHiddenFromViewer({}, 'guest')).toBe(false);
+  });
+
+  it('is null-safe', () => {
+    expect(isPhotoHiddenFromViewer(null, 'guest')).toBe(false);
+  });
+});