diff --git a/CONTRIBUTING.md b/CONTRIBUTING.md
index 676757bb..9231f728 100644
--- a/CONTRIBUTING.md
+++ b/CONTRIBUTING.md
@@ -10,8 +10,9 @@ If a feature seems to need a dependency or a build step, open an issue first.
 
 ## Development
 
-The frontend is static; edit files under `ui/` and reload. Tests use Node's
-built-in runner, with no test dependencies.
+The frontend is static; edit files under `ui/` and reload. Unit tests use Node's
+built-in runner and need nothing installed; coverage and the browser tests use
+the dev tooling in the root `package.json`.
 
 An export whose name starts with `_` exists for the tests and is not part of
 what the module offers: `_internals` for functions reached directly, `_reset*`
diff --git a/docs/frontend.md b/docs/frontend.md
index 8243d2fe..3d3a23e7 100644
--- a/docs/frontend.md
+++ b/docs/frontend.md
@@ -34,4 +34,4 @@ Each of these is a single batch request: the server fetches every configured bad
 
 ## Cache busting
 
-`?v=` on `/css/` and `/js/` URLs is a content hash rewritten at release by `scripts/bump-cache-busting.js`; do not edit it. `?v=` on `/widgets/` URLs in `widget-types.js` is manual: bump it when you change a widget's own files.
+`?v=` is a content hash rewritten at release by `scripts/bump-cache-busting.js`; do not edit one by hand. On `/css/` and `/js/` URLs the script rewrites the literal in the source. Widget iframe URLs are built from the manifest rather than written literally, so the script hashes each widget's entry files into `entryVersions` in its `widget.json`, and `widget-types.js` reads the hash from there when it builds the URL.
diff --git a/playwright.config.js b/playwright.config.js
index a7330bc7..0a5e7cd5 100644
--- a/playwright.config.js
+++ b/playwright.config.js
@@ -1,10 +1,10 @@
 // @ts-check
 /* End-to-end tests, run against the container the release publishes.
 
-   The unit suites cover logic without a DOM. These cover the things only a
-   browser shows: that a form saves what it displays, that a drag reorders and
-   the order survives a reload, that focus stays where it should, and that the
-   interface mirrors in Persian.
+   The unit suites cover logic without a DOM. These cover what only a browser
+   shows: that the admin form saves what it displays, that an edit changes only
+   what was edited, and that a saved change survives a reload. Drag reordering,
+   focus handling and the Persian mirroring are not covered here yet.
 
    Two browsers on purpose. WebKit is not decoration: the documented support
    floor is Safari 16.2, and the last two layout and keyboard problems found by
diff --git a/ui/test/cache-busting.test.mjs b/ui/test/cache-busting.test.mjs
index 1b507d80..89c68f12 100644
--- a/ui/test/cache-busting.test.mjs
+++ b/ui/test/cache-busting.test.mjs
@@ -99,3 +99,28 @@ test('the workflows call the shared checks rather than listing their own', () =>
     assert.match(workflow, /uses: \.\/\.github\/actions\/checks/, `${name} bypasses the shared checks`);
   }
 });
+
+/* The documented rule, against the mechanism.
+
+   docs/frontend.md told contributors that the widget `?v=` was manual and to
+   bump it by hand when a widget's files changed. It has not been manual since
+   entryVersions existed: the release hashes each entry file into the manifest
+   and widget-types.js reads it from there. A contributor following the document
+   would have hand-edited a value the build owns.
+
+   Pinned by mechanism rather than by sentence: what must stay true is that no
+   widget URL carries a literal stamp and that the manifest is where the value
+   comes from. */
+test('the widget cache version comes from the manifest, not a hand-written literal', () => {
+  const src = fs.readFileSync(path.join(root, 'js/widget-types.js'), 'utf8');
+  assert.match(src, /entryVersions\?\.\[file\]/, 'widget-types.js no longer reads the manifest hash');
+  const literal = /['"`]\/widgets\/[^'"`]*\?v=\d/.exec(src);
+  assert.equal(literal, null, `a hand-written widget stamp is back: ${literal && literal[0]}`);
+});
+
+test('the frontend guide describes the mechanism that exists', () => {
+  const doc = fs.readFileSync(path.join(root, '..', 'docs', 'frontend.md'), 'utf8');
+  const section = doc.slice(doc.indexOf('## Cache busting'));
+  assert.match(section, /entryVersions/, 'the guide does not mention where the widget hash lives');
+  assert.doesNotMatch(section, /is manual/, 'the guide tells contributors to bump a stamp the build owns');
+});